Analog Communication Pune University MCQs

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Source of Information”.

1. FM stands for ________

a) Frequency Modulation

b) Frequency Modulator

c) Frequent Frequent Multiplier

d) Frequency Mixer

Answer: a

Explanation: FM stands for Frequency Modulation. It is the encoding of information on a carrier wave by varying its frequency with respect to the instantaneous amplitude of the message signal. Rest other options are the components used in the process of frequency modulation.

2. Why a sinusoidal signal is considered analog?

a) It moves in both positive and negative direction

b) It is positive for one half cycle

c) It is negative for one half cycle

d) It has an infinite number of amplitudes in the range of values of the independent variable

Answer: d

Explanation: A sinusoidal wave is an analog signal. An analog electrical signal is a signal with infinite number of amplitudes in the range of values of independent variable. Analog signals can take on any value in the continuous interval.

3. The minimum height of antenna required for transmission in terms of ʎ is ________

a) 3ʎ ⁄ 2

b) ʎ ⁄ 4

c) 2ʎ

d) ʎ

Answer: b

Explanation: For effective transmission, height of antenna should be one-forth of ʎ.

(H = ʎ ⁄ 4 where ʎ = c ⁄ f ). The reason for maintaining antenna height to ʎ/4 is for matching impedance. It means that the antenna is atleast 1/4 th above ground level.

4. What do you understand by the term analog communication?

a) A method in which one of the properties of a carrier signal varies in proportion to an instantaneous value of modulation signal

b) A way for data and computer communication

c) A numerical coded communication

d) A suitable method for long distance communication

Answer: a

Explanation: Analog communication means that information is transmitted in the form of a continuous signal through the process of modulation. Rests of the options are applicable for digital communication, where coding is applied.

5. What is Demodulation?

a) Process of varying one or more properties of a periodic waveform

b) Recovering information from a modulated signal

c) Process of mixing a signal with a sinusoid to produce a new signal

d) Involvement of noise

Answer: b

Explanation: Demodulation is the process of recovering information from a modulated carrier wave while it is modulation in which properties of a periodic waveform is varied. A modulator is a device that performs modulation while the demodulator performs demodulation. A modem can perform both functions.

6. Data transmitted for a given amount of time is called ________

a) Noise

b) Power

c) Frequency

d) Bandwidth

Answer: d

Explanation: A Demodulation is a process of recovering the information signal from a modulated carrier wave, in which properties of a periodic waveform is varied. A modulator is a device that performs modulation while the demodulator performs demodulation. The process of mixing a signal with a sinusoid to produce a new signal is done by a mixer.

7. If Output can be represented as linear combination of input then ________

a) The system is linear

b) The system is causal

c) The system is non causal

d) The system is time invariant

Answer: a

Explanation: The input signal is divided into sub-components, where each sub-component is processed individually and reunited. The result is tested for additivity and homogeneity and if it satisfies both, then the system is said to be linear. It also follows superposition property.

8. Amplitude Modulation suffers from ________

a) Side-band Suppression

b) IntraPulse Modulation

c) Cross Modulation

d) Carrier Suppression

Answer: c

Explanation: Cross modulation generally occurs in receivers receiving an AM signal in the presence of other strong AM signal. The modulation from the strong signal cross modulates and appears on the weaker signal being received.

9. Medium which sends information from source to receiver is called ________

a) Transmitter

b) Transducer

c) Loudspeaker

d) Channel

Answer: d

Explanation: Channel is the medium through which information is transmitted. Transmitter is used to process the electrical signal through different aspects. The transducer is used to convert a message signal to an electrical signal. Loudspeaker is a type of Transducer.

10. Telephones send information through wires in form of ________

a) radio signals

b) electrical signal

c) electromagnetic waves

d) microwaves

Answer: b

Explanation: A telephone converts sound waves into electrical signals which are suitable for transmission over long distances, where it is converted to sound waves again, through a transducer. The essential components of a telephone are a microphone which acts as a transmitter and an earphone which acts as a receiver.

11. Cell phones sent information in form of ________

a) microwaves

b) electrical signals

c) infrared Waves

d) radio waves

Answer: d

Explanation: Cell phones transmit information in form of radio waves to communicate with each other. Radio waves are transmitted in all directions by the cell phone, and they travel at the speed of light in air or vacuum.

12. The ability of receivers to select the wanted signals among various incoming signal is called ________

a) Selectivity

b) Fidelity

c) Sensitivity

d) Modulation

Answer: a

Explanation: The ability of receiver to select wanted signal from various incoming signals is called selectivity. It rejects the other signals at closely lying frequencies. Sensitivity is the ability of the receiver to amplify weak signals. Fidelity is the feature of receiver to reproduce all modulating frequencies equally. While modulation is the process of varying one or more properties of carrier signal with respect to the modulating signal.

13. Which device is used for tuning the receiver according to incoming signal ?

a) Low pass filter

b) High pass filter

c) Zener diode

d) Varacter diode

Answer: d

Explanation: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly used in Voltage Controlled Oscillators  and RF Filters for tuning the receiver to the incoming signal or different stations.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Transmitter”.

1. Modulation is done in ________

a) Receiver

b) Transducer

c) Between transmitter and radio receiver

d) Transmitter

Answer: d

Explanation: Transmitter modulates the signal to be transmitted, by varying one of the properties of a carrier signal with respect to the instantaneous amplitude of the message signal. This process is known as modulation. Receiver demodulates the modulated signal to extract the message signal. Transducer converts the electrical signal to sound wave. Between the transmitter and the radio receiver, is the channel which acts as the medium of transmission.

2. In TV transmission, picture signal is ________ modulated.

a) DSB-SC

b) VSB

c) SSB-SC

d) Pulse

Answer: b

Explanation: All analog television systems use vestigial sideband modulation, which is a form of amplitude modulation, for transmission. In VSB, one sideband is fully transmitted and another sideband is partially removed, which further reduces the bandwidth of transmitted signal. This enables narrower channels to be used.

3. In TV transmission, sound signal is ________ modulated.

a) Phase

b) Pulse

c) Frequency

d) Amplitude

Answer: c

Explanation: Amplitude Modulation is invariably used for picture transmission while frequency modulation is generally used for transmission of sound due to its inherent advantages over amplitude modulation. It is not suitable for transmitting videos due to its large bandwidth.

4. Square Law modulators are ________

a) used for frequency modulation

b) used for pulse width modulation

c) used for amplitude modulation

d) used for phase modulation

Answer: c

Explanation: Square Law modulators are generally used for the generation of amplitude modulated signals. They have nonlinear current-voltage characteristics, such that output current or voltage varies as a square of the input.

5. Ring Modulator is ________

a) used for DSB-SC generation

b) used for SSB-SC generation

c) used for VSB generation

d) used for AM generation

Answer: a

Explanation: Ring Modulator is used for generating DSB-SC modulated waves. It is a product modulator having four diodes connected in the form of a ring. It suppresses the carrier and produces the upper-sideband and lower-sideband at the output.

6. What is the role of the transmitter in the communication system?

a) to decode a signal to be transmitted

b) to convert one form of energy into other

c) to detect and amplify information signal from the carrier

d) to produce radio waves to transmit data

Answer: d

Explanation: Transmitter is used to produce radio waves which are then sent to the antennae to transmitted. It encodes or modulates the message signal before transmission. Transducer converts a signal from one form of energy to other. Receiver detects and amplifies information signal from the carrier.

7. What is the maximum transmission efficiency?

a) 67.88%

b) 33.33%

c) 73%

d) 54.03%

Answer: b

Explanation: The maximum transmission efficiency is 33.33%. It is so because 2/3rd of the total power is contained in the carrier, which conveys no useful information. Thus, only 1/3rd of total power has useful information which is transmitted. This happens in the case of SSB-SC Modulation, where the carrier is suppressed and only either of the sidebands is allowed to pass.

8. AVC stands for ________

a) Abrupt Voltage Control

b) Audio Voltage Control

c) Automatic Volume Control

d) Automatic Voltage Control

Answer: c

Explanation: AVC stands for Automatic Volume Control. It automatically adjusts the volume of an audio signal with respect to the surrounding noise, to make the signal be heard better and also to compensate noise to some extent.

9. What is the role of Amplitude limiter in the FM receiver?

a) Filteration

b) Adjust the gain of receiver

c) Amplify a weaker signal

d) Demodulate a signal

Answer: d

Explanation: Amplitude Limiter in FM receivers are used to eliminate the amplitude changes caused due to noise interference. It does so by clipping the amplitude of output signals to the desired level, irrespective of any variations in the input signal.

10. What is Carrier swing?

a) Frequency deviation

b) Width of sideband

c) Instantaneous frequency

d) Total variation in frequency

Answer: d

Explanation: Carrier swing is defined as the total variation in frequency from the lowest to the highest point. It is equal to twice the frequency deviation of FM signal. The rest of the options are parameters in FM.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Receiver”.

1. Demodulation is done in ________

a) Channel

b) Receiver

c) Receiving antenna

d) Transducer

Answer: b

Explanation: Demodulation refers to extracting the original message signal from a transmitted modulated wave. The extraction of the message signal is generally carried out in the receiver. Channel is the medium through which the modulated message signal is transferred and Antenna receives the transmitted signal. Transducer converts the electrical signal to sound waves and vice-versa.

2. What is Fidelity?

a) Equally amplifies all the signal frequencies at receiver

b) Ability of receiver to select wanted signal from various incoming signal

c) Minimum magnitude of input signal required to produced a specified output

d) Ability to amplify weak signals

Answer: a

Explanation: Fidelity is the ability of the receiver to reproduce all modulating signals, equally, without any distortion. The ability of receiver to select wanted signal from various incoming signals is called Selectivity while Sensitivity is the minimum magnitude of input signal required to produce a specified output. It is the ability to amplify weak signals.

3. In a receiver, noise is usually developed at ________

a) Audio stage

b) Receiving antenna

c) RF stage

d) IF stage

Answer: c

Explanation: Ability of receiver to selected only wanted signal, and reject other frequencies, out of the various incoming signals, helps the receiver to operate more efficiently. However, at times, the RF amplifier allows a frequency lying close to the desired frequency, to pass to the next stage. This other frequency is undesired and later on is responsible for production of image frequency. Thus, noise is usually developed at RF stage.

4. Which oscillator is used as a local oscillator in radio receiver?

a) Wien-bridge

b) Hartley

c) Crystal

d) Phase Shift

Answer: b

Explanation: Oscillator which is used as a local oscillator in radio receiver is generally a tuned circuit. This tuned circuit consists of inductors and capacitors to determine the resonant frequency, therefore it is an LC tuned circuit. Out of the four options, only Hartley Oscillator has an LC resonant tank circuit.

5. Process of recovering information signal from received carrier is known as ________

a) Sensitivity

b) Selectivity

c) Demodulation

d) Fidelity

Answer: c

Explanation: Demodulation means extracting information or message signal from the transmitted modulated wave, while minimum magnitude of input signal required to produced a specified output is known as Sensitivity. The ability of receiver to select wanted signal from various incoming signals is called Selectivity. Fidelity means reproducing all modulating frequencies equally, without any distortion.

6. What is the use of a varactor diode in radio receiver?

a) Demodulation

b) Mixing

c) Multiplexing

d) Tuning

Answer: d

Explanation: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly used in Voltage Controlled Oscillators  and RF Filters for tuning the receiver to the incoming signal or different stations.

7. What is the function of radio receiver?

a) to detect and amplify information signal from the carrier

b) to modulate a message signal

c) to produce radio waves

d) to convert one form of energy into other

Answer: a

Explanation: Receiver is to detect and amplify information signal from the carrier. Transmitter is used to modulate message signal and produce radio waves. Transducer is used to convert one signal form of energy into another form.

8. Figure of merit is ________

a) Ratio of output signal to noise ratio to input signal to noise ratio

b) Ratio of input signal to noise ratio to output signal to noise ratio

c) Ratio of output signal to input signal to a system

d) Ratio of input signal to output signal to a system

Answer: a

Explanation: Figure of merit is a numerical quantity based on the characteristic of system that represents a measure of efficiency or effectiveness. It is defined as the ratio of output signal to noise ratio to input signal to noise ratio.

9. Superheterodyne principle provides selectivity at ________

a) RF stage

b) IF stage

c) Demodulating Stage

d) Audio Stage

Answer: b

Explanation: A superheterodyne receiver uses frequency mixing to convert the received high frequency signal to a fixed lower intermediate frequency , which can be processed more conveniently than original received frequency. Thus, the principle of selectivity is applied at the IF stage as it consists of very efficient filters to only select a wanted signal and pass it to the Demodulating Stage.

10. A heterodyne frequency changer is ________

a) Mixer

b) Demodulator

c) Modulator

d) Local Oscillator

Answer: a

Explanation: A mixer is a nonlinear electrical circuit that multiplies two signal frequencies applied to it, and produces a new frequency. Mixers are widely used to shift signals from one frequency range to other, which is known as heterodyning process. Generally, Local Oscillator generates a frequency to be applied at one of the input terminals of the mixer. Demodulator decodes the message signal from modulated signal, while modulator encodes message signal for transmission.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Channel”.

1. Notch is a ________

a) High pass filter

b) Low pass filter

c) Band stop filter

d) Band pass filter

Answer: c

Explanation: Notch filter is a band stop filter that allows most frequencies to pass through it, except frequencies in a specific range. It is just opposite of a band-pass filter. High pass filter allows higher frequencies to pass while Low pass filter allows lower frequencies to pass through it.

2. Sin wave is ________

a) Aperiodic Signal

b) Periodic Signal

c) Random Signal

d) Deterministic Signal

Answer: b

Explanation: Periodic signal is that which repeats itself after a regular interval. Sin wave is a periodic function since it’s value can be determined at any point of time, as it repeats itself at a regular interval. Aperiodic Signal does not repeat itself at regular interval of time. Random signals are the signals which have uncertain values at any time. While Deterministic signals are the signals which are constant over a period of time.

3. What is the role of channel in communication system?

a) acts as a medium to send message signals from transmitter to receiver

b) converts one form of signal to other

c) allows mixing of signals

d) helps to extract original signal from incoming signal

Answer: a

Explanation: Channel acts as a medium to transmit message signal from source transmitter to the destination receiver. Transducer converts a signal from one form of energy to other. Mixer allows mixing of signals while Demodulator helps to extract original message signal from incoming signal.

4. Sum of a periodic and aperiodic signal always be an aperiodic signal.

a) True

b) False

Answer: b

Explanation: Periodic signal is a signal which repeats itself after a regular interval. While Aperiodic Signal does not repeat itself at regular interval of time.

For example: Let f = sin, be a periodic function with period 2π and g = −sin + sin, be an aperiodic function. Now the sum of both i.e. f + g = sin, which is a periodic function.

Therefore, the sum of a periodic and aperiodic signal can be periodic.

5. Noise is added to a signal ________

a) In the channel

b) At receiving antenna

c) At transmitting antenna

d) During regeneration of information

Answer: a

Explanation: Noise is an unwanted signal that gets mixed with the transmitted signal while passing through the channel. The noise interferes with the signal and provides distortion in received signal. The transmitting antenna transmits modulated message signal while the receiving antenna receives the transmitted signal. Regeneration of information refers to demodulating the received signal to produce the original message signal.

6. Agreement between communication devices are called ________

a) Transmission medium

b) Channel

c) Protocol

d) Modem

Answer: c

Explanation: Protocol is a set of rules that looks after data communication, by acting as an agreement between communication devices. Channel is the transmission medium or the path through which information travels. Modem is a device that modulates and demodulates data.

7. What is the advantage of superheterodyning?

a) High selectivity and sensitivity

b) Low Bandwidth

c) Low adjacent channel rejection

d) Low fidelity

Answer: a

Explanation: The main advantage of superheterodyning is that it provides high selectivity and sensitivity. It’s bandwidth remains same. It has high adjacent channel rejection and high fidelity.

8. Low frequency noise is ________

a) Flicker noise

b) Shot noise

c) Thermal noise

d) Partition Noise

Answer: a

Explanation: Flicker noise is a type of electronic noise which is generated due to fluctuations in the density of carrier. It’s also known as 1/f as it’s power spectral density increases with a decrease in frequency or increase in offset from a signal.

9. Relationship between amplitude and frequency is represented by ________

a) Time-domain plot

b) Phase-domain plot

c) Frequency-domain plot

d) Amplitude-domain plot

Answer: c

Explanation: Relationship between amplitude and frequency is represented by a frequency-domain plot. Also, it represents the relation between phase and frequency. While a time-domain plot shows how a signal varies over time.

10. A function f is even, when?

a) f = -f

b) f = f

c) f = -ff

d) f = ff

Answer: b

Explanation: Geometrically a function f is even, if plot of the function is symmetric over y-axis. Algebraically, for any function f to be even, f = f.

While for a function f to be odd, f = -f.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Frequency Domain Description”.

1. What is Amplitude Modulation?

a) Change in amplitude of carrier according to modulating signal amplitude

b) Change in frequency of carrier according to modulating signal amplitude

c) Change in amplitude of carrier according to modulating signal frequency

d) Change in amplitude of modulating signal according to carrier signal amplitude

Answer: a

Explanation: Amplitude modulation is a modulation process in which amplitude of carrier wave is varied with respect to amplitude of the message signal to be transmitted. Whereas, Frequency modulation is a modulation process in which frequency of carrier wave is varied with respect to amplitude of the message signal to be transmitted.

2. Frequency components of an AM wave are?

a) Carrier frequency (ω c ) with amplitude A

b) Lower side band (ω c + ω m ) having amplitude mA ⁄ 2

c) Upper side band (ω c – ω m ) having amplitude mA ⁄ 2

d) Carrier frequency (ω c /2) with amplitude A

Answer: a

Explanation: The frequency components of AM waves are: Carrier frequency (ω c ) with amplitude A, Lower sideband (ω c – ω m ) having amplitude mA/2 and Upper side band (ω c + ω m ) having amplitude mA ⁄ 2 (where m represents modulation index, A is the amplitude of the carrier signal, ω m is the amplitude of the message signal).

3. In amplitude modulation frequency and phase of carrier ________

a) varies simultaneously

b) varies alternately

c) initially varies but become same after sometime

d) remains constant

Answer: d

Explanation: In AM, amplitude of carrier signal varies according to instantaneous amplitude of baseband signal. The frequency and phase of carrier signal remains constant.

4. Envelope of AM wave has the same shape as the message of baseband signal.

a) True

b) False

Answer: a

Explanation: Modulation Envelope of an AM wave is said to follow the outline of the message signal when carrier, upper sideband and lower sideband are combined in a single impedance and observed on time versus amplitude plot. Thus, AM wave has same shape as the message signal.

5. When aliasing takes place?

a) Sampling signals less than Nyquist Rate

b) Sampling signals more than Nyquist Rate

c) Sampling signals equal to Nyquist Rate

d) Sampling signals at a rate which is twice of Nyquist Rate

Answer: a

Explanation: Aliasing causes different signals to become indistinguishable during sampling. It happens because sampling rate is less than Nyquist rate. In order to avoid aliasing, signals should be sampled at a rate twice of Nyquist rate.

6. Why the Synchronous detection of AM signals is considered as a disadvantage?

a) Needs additional system for synchronization of carrier

b) Receiver is available at cheap prices

c) Needs less number of system as estimated for generation of carrier

d) Receiver is not complex

Answer: a

Explanation: Disadvantage of synchronous detection of AM signal are that it needs an additional system for generation of carrier. It also needs additional system for synchronization of carrier. Moreover receiver is complex and costly.

7. Which devices did we use for AM Demodulation?

a) Envelope detector and Square law demodulator

b) PLL detector and Foster-Seeley discriminator

c) Ratio detector and Slope detector

d) Only quadrature detector

Answer: a

Explanation: AM signals can be demodulated using Square law demodulator or Envelope detector. Demodulator extracts information from received AM signal by decoding it. Other options are the demodulators for FM signal.

8. Square Law modulators ________

a) used for amplitude modulation

b) have non linear current-voltage characteristics

c) have non linear current-voltage characteristics as well as used for Amplitude Modulation

d) used for frequency modulation

Answer: c

Explanation: Square law modulators are used for amplitude modulation and have non-linear current-voltage characteristics. The output of Square law demodulator is said to vary with respect to square of the input. They are highly linear in low voltage region.

9. What do you understand by low level AM?

a) Output power is low

b) Modulation is done at high power of carrier and modulating signal

c) Collector Modulation Method is low level AM

d) Output power is high

Answer: a

Explanation: In low level AM, modulation is done at low power of carrier and modulating signal therefore output power is low. Therefore, power amplifiers are used to boost the carrier and modulating signal. Collector Modulation Method is high level AM. At high-level AM, output power is high.

10. What do you understand by high level AM?

a) Output power is low

b) Modulation is done at high power of carrier and modulating signal

c) No need to boost the carrier and modulating signal

d) Modulation is done at low power of carrier and modulating signal

Answer: b

Explanation: For high level AM, modulation is done at high power of carrier and modulating signal, so power amplifiers are not used to boost the carrier and modulating signal. Therefore, output power is high. At low-level AM, output power is low.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Single Tone Modulation”.

1. For Amplitude Modulation, Emitter modulator ________

a) Operates in class C mode

b) Has a low efficiency

c) Output power is high

d) Operates in class B mode

Answer: b

Explanation: Emitter Modulator operates in class A region. It has very low efficiency. The output power is low so for modulation at high level, it is not suitable.

2. Why AM is used for broadcasting?

a) More immune to noise

b) Less transmitting power is required

c) It has high fidelity

d) Avoids Receivers Complexity

Answer: d

Explanation: AM detectors are generally, square law demodulators or envelope detectors at the receiver. As AM detectors at the receiver end are simple circuits and avoid any kind of complex structure, therefore, AM used for broadcasting.

3. Singletone amplitude modulation ________

a) consists of only one frequency component

b) contains a large number of frequency components

c) contains no frequency components

d) contains infinite number of frequency components

Answer: a

Explanation: Single tone modulation consists of only one frequency component in the baseband or message signal. Thus, modulation of carrier wave is done by a single frequency component only.

4. AM spectrum consists of ________

a) Carrier frequency

b) Upper sideband

c) Lower sideband

d) Carrier frequency with both upper and lower sideband

Answer: d

Explanation: Spectrum of Am wave consists of a carrier with upper sideband and lower sideband. If carrier frequency is Wc, then the two sidebands produced by it are  and , where Wm is the frequency of the message signal. The amplitude of the carrier is A and that of the two sidebands are mA/2, where m is the modulation index.

5. The minimum channel Bandwidth is used by which modulation technique?

a) VSB

b) SSB-SC

c) DSB-SC

d) AM

Answer: b

Explanation: A signal has two sidebands which are exactly the mirror images of each other. So we can remove one side band which further reduces its bandwidth. In SSB-SC modulation technique, the carrier is suppressed and only either of the sidebands is transmitted. Thus, SSB-SC has minimum channel Bandwidth.

6. Neper is ________ decibel.

a) 20/

b) 20ln10

c) Same as

d) Exactly twice of

Answer: a

Explanation: Neper is a logarithmic unit used for finding ratios of power quantities. Like decibel it is also a dimensionless unit. 1Np = 20/ln⁡10 = 8.686 db.

7. AM broadcast station transmits modulating frequency upto 6KHz. If transmitting frequency is 810KHz, then maximum and lower sidebands are ________

a) 816KHz and 804KHz

b) 826KHz and 804KHz

c) 916KHz and 904KHz

d) 822KHz and 816KHz

Answer: a

Explanation: Maximum frequency = 810 + 6 = 816KHz and Minimum frequency = 810 – 6 = 804KHz. Moreover it has a bandwidth of  = 12KHz.

.

8. Find lower frequency component in AM wave, given that highest frequency component is 900KHz and bandwidth is 12KHz?

a) 832KHz

b) 600KHz

c) 868KHz

d) 888KHz

Answer: d

Explanation: Highest frequency component is 900KHz and bandwidth is 12KHz. So lower frequency component is 900 – 12 = 888KHz.

.

9. Amplitude Modulated wave is ________

a) Sum of carrier and modulating wave

b) Product of carrier and modulating wave

c) Difference of carrier and modulating wave

d) Sum of carrier and its product with modulating wave

Answer: a

Explanation: The modulation of a carrier wave by varying its amplitude with respect to amplitude of baseband signal is known as amplitude modulation. It is represented as,

s = [1 + mx] c,

where, x = Modulating Wave, m=Modulating Index

c = Carrier Wave = A c (Cos ω c ) t

Thus, Amplitude Modulated wave is the Sum of carrier and its product with modulating wave.

This set of Analog Communications Questions and Answers for Campus interviews focuses on “Power Relations in AM Waves”.

1. Calculate power in each sideband, if power of carrier wave is 176W and there is 60% modulation in amplitude modulated signal?

a) 13.36W

b) 52W

c) 67W

d) 15.84W

Answer: d

Explanation: Modulation index = 0.6 and Pc = 176W. Power in sidebands may be calculated as

analog-communications-questions-answers-campus-interviews-q1

2. For 100% modulation, power in each sideband is ________ of that of carrier.

a) 50%

b) 70%

c) 60%

d) 25%

Answer: d

Explanation: Modulation index = 1. Power in sidebands may be calculated as

analog-communications-questions-answers-campus-interviews-q2

3. Overmodulation results in ________________

a) Distortion

b) Weakens signal

c) Strengthens the signal

d) provides immunity to noise

Answer: a

Explanation: When instantaneous level of modulating signal exceeds the value necessary to provide 100% modulation, the signal is said to over-modulated. In other words, when modulation index is greater than 1, it results in Overmodulation. Thus, Overmodulation results in distortion of the modulating signal.

4. The maximum power efficiency of an AM modulator is?

a) 25%

b) 33%

c) 66%

d) 100%

Answer: b

Explanation: Efficiency ή = m 2 / (m 2 + 2), m=Modulation Index

For maximum efficiency m = 1 so, ή = 1/ = 1/3

and ή% = x100 = 33%.

5. Noise performance of a square law demodulator of AM signal is?

a) Better than that of synchronous detector

b) Weaker than that of synchronous detector

c) Better than that of envelope detector

d) Weaker than that of envelope detector

Answer: a

Explanation: Process of recovering message signal from received modulated signal is called demodulation. It is exactly opposite to modulation. There are two most used AM demodulators: Square Law Demodulator and Envelope Demodulator. Noise performance of Square Law Demodulator is far better than that of Synchronous Detector.

6. For getting 100% modulation, carrier amplitude should ________

a) exceed signal amplitude

b) be equal to signal amplitude

c) be lesser than signal amplitude

d) be equal to 0

Answer: b

Explanation: Modulation index is the amount of modulation present in a carrier wave. It is also described as the ration of the amplitude of message signal to that of carrier signal.

Modulation Index  = V m /V c , where V m is maximum baseband or message signal amplitude and V c is maximum carrier signal amplitude. So for m = 1, V m should be equal to V c .

7. For 100% modulation, total power is?

a) same as the power of unmodulated signal

b) twice as the power of unmodulated signal

c) four times as the power of unmodulated signal

d) one and half times as the power of unmodulated signal

Answer: d

Explanation: Total power, P t = P c (1 + m 2 ⁄ 2 ), where m is Modulated Signal, P c is Power of Unmodulated Signal or Carrier Signal.

So, for m=1,

P t = P c (1 + 1 2 /2) = 1.5 P c .

8. An AM signal is represented by x = ) Cos(2πt x 10 2 t)V. What is the value of modulation index?

a) 0.7

b) 0.066

c) 0.341

d) 0.916

Answer: b

Explanation: Given equation can be written as 30).

Comparing it with general AM equation, s = A c (1 + mA m cos(w m t)) cos(w c t),

Where, A c = Amplitude of Carrier Signal, A m = Amplitude of Message Signal

m=Modulation Index

So modulation index = 0.066.

9. An AM signal is represented by x = ) Cos(2πt x 10 2 t)V. Carrier power of the wave is?

a) 555W

b) 675W

c) 450W

d) 310W

Answer: c

Explanation: analog-communications-questions-answers-campus-interviews-q9

Hence P c = 450W.

10. An AM signal is represented by x = ) Cos(2πt x 10 2 t)V. Find the total power of amplitude modulated wave?

a) 453W

b) 675W

c) 789W

d) 451W

Answer: d

Explanation: P t = P c (1 + b m 2 ⁄ 2 ) * p c

So, here, m = 0.066, P c = 450W

P t = )*450 = 451W.

11. An AM signal is represented by x = ) Cos(2πt x 10 2 t)V. What is its sideband power?

a) 4W

b) 1W

c) 3W

d) 2W

Answer: b

Explanation: Sideband power i = (m 2 * P c )/2 = (P t – P c ) i.e. 451 – 450 = 1W.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “AM Wave Representation”.

1. AM waves is represented by which equation?

a) [1 + m].c

b) [1 – m].c

c) [1 + m].2c

d) [1 + 2m].c

Answer: a

Explanation: Amplitude wave is represented by [1 + um].c, where c is carrier signal, m is message signal, u is Modulation Index.

Generally, c = A c cos(w c t), A c = Amplitude of Carrier Signal.

2. For attenuation of high frequencies we can use ________

a) inductor

b) shunt capacitance

c) series capacitance

d) combination of inductor and resistor

Answer: b

Explanation: Capacitive reactance, Xc is low for high frequencies as Xc=, where w is the frequency and C is the capacitance. Due to this, the high frequencies are shunted to ground and are not transmitted.

3. If each element of signal occupies 40ms, determine its speed?

a) 20 bauds

b) 25 bauds

c) 40 bauds

d) 0.05 bauds

Answer: b

Explanation: analog-communications-questions-answers-am-wave-representation-q3

4. A modem is classified as low if speed of data rate is ________

a) upto 600bps

b) upto 200bps

c) upto 400bps

d) upto 500bps

Answer: a

Explanation: Modem is device that can modulate carrier wave as well as demodulate transmitted modulated signal to decode the original information. When data rate in bps is upto 600, modem is considered having low speed.

5. Modulation is also called detection.

a) True

b) False

Answer: b

Explanation: Modulation is encoding the message signal for efficient transmission. Whereas, Demodulation is the process to extract or decode the original message signal from the transmitted modulated signal. Demodulation is also called detection.

6. It is suitable to connect woofer from the input through ________

a) band pass filter

b) band stop filter

c) low pass filter

d) high pass filter

Answer: c

Explanation: Woofer is considered as a low frequency loud speaker. It has a range from 10Hz to 500Hz. So it is better to use low pass filter for connection. Los Pass filter allows low frequencies to pass while high pass filter allows high frequencies to pass. Band pass filter allows a range of frequencies to pass whereas. Band stop filter does the opposite.

7. The radiation at right angles is zero means ________

a) l = ʎ

b) l = ʎ ⁄ 4

c) l = 2 ʎ

d) l = ʎ ⁄ 2

Answer: a

Explanation: Antenna is used for converting electromagnetic radiation into electric currents or vice-versa. If the length of antenna is equal to the whole wavelength then the radiation at right angles is zero.

8. Power of carrier wave is 500W and modulation index is 0.25. Find its total power?

a) 500W

b) 415W

c) 375W

d) 516W

Answer: d

Explanation: Total Power (P t ) = (1+m 2 /2)*P c

So, here, m = 0.25, P c = 500W

P t = (1+(0.25 2 /2))*500 = 516W.

9. Commercial frequency deviation is ________

a) 75 KHz

b) 80 KHz

c) 85 KHz

d) 65 KHz

Answer: a

Explanation: Frequency deviation is the difference between an FM modulated frequency and the carrier frequency. Commercial FM broadcasting uses a maximum frequency deviation of 75 KHz and maximum modulating frequency is approximately 15KHz.

10. Which of the following cannot be the Fourier series of a periodic signal?

a) x = 2Cost + 4Cos7t

b) x = 2Cosπt + 4Cos7t

c) x = Cost + 0.7

d) x = 2Cost + 4Sin7t

Answer: c

Explanation: x = Cost + 0.7 does not follow Dirchlet’s conditions. Fourier series of a periodic signal will only be applicable if it satisifies Dirchlet’s conditions firstly. Dirichlet integral states that a finite number should have finite number of discontinuities and also have finite number of extrema. x doesn’t satisfy any of the criteria, whereas other options satisfy Dirchlet’s conditions. Thus, x = Cost + 0.7, cannot be the Fourier series of a periodic signal.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Generation of AM Waves”.

1. Which of the following devices is used to generate AM waves?

a) Square-law modulator

b) Reactance modulator

c) Transmitter

d) Transducer

Answer: a

Explanation: AM signals are generated by Square-law modulators. The input for generating AM signal should be of type ) instead of m. Square-law modulator sums carrier and information signal, then passes them through a non-linear device.

2. What is the disadvantage of FM over AM?

a) high modulating power is needed

b) requires high output power

c) large bandwidth required

d) high noise is produced

Answer: c

Explanation: Advantage of FM over AM is that the amplitude of an FM wave remains constant. In FM, the power of transmitted wave depends on amplitude of unmodulated carrier wave and hence it is constant. FM is less prone to noise compared to AM. However, wide-band FM has a wider bandwidth than AM as it’s BW is given by Carson’s rule which = 2*f m , where β = Frequency Modulation Index and f m is frequency of modulating signal. And BW of AM = 2*f m .

3. For low level amplitude modulation, amplifier must be ________

a) Class C amplifier

b) Class B amplifier

c) Class D amplifier

d) class A amplifier

Answer: a

Explanation: In low level AM, modulation is done at low power of carrier and modulating signal therefore output power is low. Therefore, power amplifiers are used to boost the carrier and modulating signal. Thus, Class C amplifier is used.

4. Approximate range of a cordless telephone is ________

a) 900m

b) 100m

c) 1000m

d) 475m

Answer: b

Explanation: Cordless telephone is one in which the handset is portable and communicates with the body of the phone by radio waves instead of being connected by a cord. The range depends on the quality of instrument and is about 90m to 100m.

5. A wave is modulated by two sin waves having modulation indices of 0.3 and 0.5. Find the total modulation index?

a) 0.1

b) 0.7

c) 0.58

d) 0.35

Answer: c

Explanation: Given that m1 = 0.3 and m2 = 0.5. Total modulation index will be equal to analog-communications-questions-answers-generation-am-waves-q5 . By substituting values we have analog-communications-questions-answers-generation-am-waves-q5a which is equal to 0.58.

6. Carrier wave carries information.

a) True

b) False

Answer: b

Explanation: It is a high frequency electro-magnetic wave. A carrier wave does not have any information. One of the properties like amplitude, frequency or phase of the carrier are modulated with respect to an input signal for the purpose of conveying information.

7. What can we do to eliminate distortion in the picture?

a) use a longer transmission line

b) change the antenna orientation

c) use a short transmission line

d) connect a booster

Answer: b

Explanation: According to modulation, length of antenna should be one fourth of wavelength. If distortion occurs whether in television or at any other place, simplest way to eliminate this is to change the orientation of antenna.

8. For 100% amplitude modulation, the power in upper sideband when carrier power is to be 100W?

a) 100W

b) 75W

c) 25W

d) 50W

Answer: c

Explanation: Modulation index, m = 100% = 1. Power in sidebands is (P c x m 2 ⁄ 4 ). By substituting the values, we have (100 x 1 ⁄ 4 ) which is equal to 25W.

Modulation index, m = 100% = 1.

Power in sidebands = (P c x m 2 /4), P c = Power of Carrier

By substituting the values, we have  = 25W.

9. Modem is considered as high speed if data rate is ________

a) 10000

b) 20000

c) 5000

d) 30000

Answer: c

Explanation: For data rate in the range 2000 to 10500 bps, modem is designated as high speed. Modem is a combination of modulator and demodulator. Modulator tends to encode message signal and demodulator decodes the message signal from the modulated waveform.

10. Scanning always takes place from ________

a) right to left

b) left to right

c) left to right for odd fields and right to left for even fields

d) left to right for even fields and right to left for odd fields

Answer: b

Explanation: Scanning is mostly used in TV to obtain continuous frames and to provide motion of picture. Scanning always takes place from left to right.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Detection of AM Waves”.

1. Detection is same as ________

a) Modulation

b) Mixing

c) Filtering

d) Demodulation

Answer: d

Explanation: Process of extracting the original message signal from the received modulated signal is called demodulation. Demodulation is also known as detection.

2. Most commonly used modulation system for telegraphy is ________

a) Multi-tone modulation

b) Single tone modulation

c) PCM

d) FSK

Answer: d

Explanation: FSK  is a method to transmit digital signals, which are in form of binary data. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for communication between computers, over telephone lines. Single tone modulations deals with message signal having single frequency component, whereas, Multi-tone modulation deals with message signal having multiple frequency components.

3. What do you understand by the term “carrier”?

a) waveform with constant frequency, phase and amplitude

b) waveform for which frequency, amplitude or phase is varied

c) waveform with high amplitude, low frequency and constant phase

d) waveform to be transmitted

Answer: b

Explanation: A carrier wave is modulated in terms of amplitude, frequency or phase, with respect to an input signal for conveying information. Carrier wave has generally higher frequency than the input signal.

4. According to Fourier analysis, square wave can be represented as ________

a) fundamental sine wave and even harmonics

b) fundamental sine wave and odd harmonics

c) fundamental sine wave and harmonics

d) fundamental and sub harmonic sine wave

Answer: b

Explanation: A square wave is a non-sinusoidal periodic waveform with steady frequency, in which the amplitude alternates between a fixed maximum and minimum value. According to Fourier analysis, an ideal square wave, with amplitude one, can be represented as an infinite sum of sinusoidal waves. An ideal square wave contains only components of odd integer harmonics.

5. PDM is generated by ________

a) Bistable multivibrator

b) Monostable multivibrator

c) Astable multivibrator

d) Schmitt trigger

Answer: b

Explanation: PDM  is used to produce an analog signal with the help of a digital source. Monostable multivibrators are used to generate a single output pulse of a particular width. Its output is either high or low when a suitable external pulse is applied.

6. Mass of any moving system is represented by ________

a) a resistance

b) a conductance

c) a resistivity

d) an inductance

Answer: d

Explanation: Inductance can also be seen as electromagnetic inertia, a property that opposes changes in electric currents and magnetic fields. Mass has inertia so it is represented by an inductance.

7. Contrast function in TV is done by ________

a) Luminance amplifier

b) Schmitt trigger

c) Band Pass Filter

d) Chroma amplifier

Answer: a

Explanation: Luminance amplifier is mostly used by the Contrast Function, in TV sets. It helps to changes the contrast or picture quality of television with respect to the received visual signals, by making the contrast optimum.

8. Bandwidth of RF amplifier for a color TV receiver is ________

a) equal to channel width

b) more than channel width

c) less than channel width

d) twice of channel width

Answer: b

Explanation: RF amplifiers are tuned amplifiers in which the frequency of operation is controlled by a tuned circuit. Bandwidth of RF amplifier is generally kept a little more than channel so that there is no problem in reception.

9. FSK system involves ________

a) frequency modulation

b) pulse modulation

c) amplitude modulation

d) phase modulation

Answer: a

Explanation: FSK  is a method to transmit digital signals, which are in form of binary data. FSK i.e. Frequency Shift Keying involves frequency modulation that assigns bit values to discrete frequency while ASK assigns bit values to discrete amplitude.

10. Diameter of antenna is doubled. The maximum range will ________

a) be doubled

b) be halved

c) become four times

d) decrease to one fourth

Answer: a

Explanation: Range of antenna is directly proportional to antenna diameter. So if diameter of antenna is doubled its range also doubled.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Problems of AM”.

1. If the modulating frequency of a carrier wave varies between 700Hz and 7KHz, find it’s bandwidth?

a) 10 KHz

b) 23 KHz

c) 17.3 KHz

d) 12.6 KHz

Answer: d

Explanation: Modulating Frequency (f m ) = V max -V min , where,

V max = Maximum Amplitude of an amplitude modulated,

V min = Minimum amplitude of an amplitude modulated,

f m = 7KHz – 700Hz = 6.3KHz

Bandwidth = 2f m = 2 x 6.3 = 12.6 KHz.

2. A 400W carrier wave is modulated to a depth of 65%. Find the total power of modulated wave?

a) 512.5W

b) 493W

c) 484.5W

d) 609.6W

Answer: c

Explanation: Total power, P t = P c (1 + µ 2 ⁄ 2 ), where P c = Carrier Power = 400W

where Modulation Index µ = 0.65,

so P t = 400 (1 + 0.65 2 ⁄ 2 ). On solving it we get P t = 484.5W.

3. Inductance and capacitance of a line is 0.8 μH ⁄ m and 32 pF ⁄ m . Find Z 0 ?

a) 158

b) 166

c) 143

d) 127

Answer: a

Explanation: The characteristic impedance or surge impedance (Z 0 ) of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line; which is, a wave travelling in one direction in the absence of reflections in the other direction.

analog-communications-questions-answers-problems-am-q3 .

4. Find VSWR of a line having maximum and minimum value equals to 120mV and 40mV respectively?

a) 3

b) 2

c) 1

d) 4

Answer: a

Explanation: The voltage standing wave ratio  is defined as the ratio of the maximum to minimum voltage on a loss-less line. In this way, the VSWR is measured at a particular point and the voltage maxima and minima do not need to be determined along the length of the line.

analog-communications-questions-answers-problems-am-q4

5. A 1000 KHz carrier is modulated with 300 Hz, 8000 Hz and 2 KHz waves. Determine the frequencies whose chances of occurring in output is least?

a) 1000 KHz

b) 1002 KHz

c) 998 KHz

d) 999.2 KHz

Answer: a

Explanation: Frequencies present in output are of the form f c ± f m , f c ± 2f m , f c ± 3f m . And 1000 KHz is a multiple of none in the range. Whereas, rest options are one of the multiples in the range.

6. If average power of a transmitter is 4kW and maximum power is 20000KW. What is its duty cycle?

a) 2 x 10 -3

b) 2 x 10 -4

c) 3 x 10 -3

d) 0.05

Answer: b

Explanation: Duty cycle is the proportion of time during which a component, device, or system is operated. The duty cycle can be expressed as a ratio or as a percentage.

analog-communications-questions-answers-problems-am-q6

7. The voltage and electric current of a line are respectively 5kV and 1000μA. Find its power?

a) 12W

b) 13W

c) 5W

d) 10W

Answer: c

Explanation: Electrical power is the rate at which electrical energy is converted to another form, such as motion, heat, or an electromagnetic field.

Power, P = V x I. By substituting the values of voltage and current, we have P = (5×10 3 )(1000×10 -6 ) = 5W.

8. ________ microphones works on piezoelectric effect.

a) Crystal

b) Carbon

c) Moving coil

d) Condenser

Answer: a

Explanation: Piezoelectric effect is the ability of materials to generate an electric charge in response to applied mechanical stress. Crystals which demonstrate the piezoelectric effect produce voltages when they are deformed. The crystal microphone uses a thin strip of piezoelectric material attached to a diaphragm. The two sides of the crystal acquire opposite charges when the crystal is deflected by the diaphragm.

9. If modulation index of an AM wave is increased from 1.5 to 2, then the transitted power ________

a) remains same

b) increases by 20%

c) increases by 41%

d) increases by 50%

Answer: c

Explanation: When m=1.5, transmitted power

analog-communications-questions-answers-problems-am-q9 .

= 0.41 x 100

= 41%

Therefore, there is an increase in total power by 41%.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “FDM System”.

1. Frequency difference between WDM  and FDM  is ________

a) 1

b) 0

c) slightly greater than 1

d) infinity

Answer: d

Explanation: WDM  is partly similar to FDM . FDM is used for signal transmission through a twisted-pair cable while WDM is used to transmit signals through optical fiber cables. Frequency difference between WDM and FDM is infinity.

2. FDM stands for ________

a) Frequency Density Multiplexing

b) Frequency Difference Multiplexing

c) Frequency Division Multiplexing

d) Frequency Data Manager

Answer: c

Explanation: FDM stands for Frequency Division Multiplexing. The total bandwidth is divided into a series of non-overlapping frequency bands and each band is used to carry a separate signal.

3. TDM stands for ________

a) Time Division Multiplexing

b) Time Difference Multiplexing

c) Time Duration Multiplexing

d) Time Data Manager

Answer: a

Explanation: TDM stands for Time Division Multiplexing. It is used to transmit and receive independent signals over a common signal path with the help of synchronized switches.

4. TDM and FDM are used to multiplex multiple signals into a single carrier.

a) False

b) True

Answer: b

Explanation: Multiplexing is the method of combining two or more than two signals into one, in such a way that each individual signal can be retrieved at the receiver. Both TDM and FDM are used to multiplex different signals into a single carrier. However, TDM is used to transmit and receive independent signals over a common signal path with the help of synchronized switches. Whereas, in case of FDM, the total bandwidth is divided into a series of non-overlapping frequency bands and each band is used to carry a separate signal.

5. What is Synchronous TDM?

a) gives same amount of time to each device

b) gives same amount of frequency to each device

c) gives variable time to each device

d) gives variable frequency to each device

Answer: a

Explanation: TDM is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing. Synchronous TDM gives exactly the same amount of time to each connected device. It allocates time to every device even if a device has nothing to transmit.

6. FDM is an analog multiplexing technique used to combines ________

a) analog signals

b) digital signals

c) both analog and digital signals

d) alternatively passes analog and digital signals

Answer: a

Explanation: Frequency Division Multiplexing  is a networking technique in which multiple data signals are combined for simultaneous transmission via a shared communication medium. FDM uses a carrier signal at a discrete frequency for each data stream and then combines many modulated signals. FDM is used to multiplex multiple analog signals. FDM is applied when the bandwidth of the link is greater than the combined bandwidth of signals to be transmitted.

7. Frequency Division Multiplexing  is based on orthogonality.

a) True

b) False

Answer: a

Explanation: Frequency Division Multiplexing  is a networking technique in which multiple data signals are combined for simultaneous transmission via a shared communication medium. FDM uses a carrier signal at a discrete frequency for each data stream and then combines many modulated signals. Orthogonal frequency division multiplexing is used to encode multiple carrier frequencies. It is mainly used for latest wireless telecommunications.

8. Which multiplexing technique transmits digital signals?

a) FDM

b) TDM

c) WDM

d) Both FDM and TDM

Answer: b

Explanation: Time Division Multiplexing is used to transmit digital signals. FDM and WDM techniques are used to transfer analog signals. WDM  is partly similar to FDM . FDM is used for signal transmission through a twisted-pair cable while WDM is used to transmit signals through optical fiber cables.

9. To get constant time delay, we should use ________

a) FDM technique

b) WDM technique

c) Synchronous TDM

d) Non synchronous TDM

Answer: c

Explanation: TDM is a method of allowing multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing. Synchronous TDM gives exactly the same amount of time to each connected device. It allocates time to every device even if a device has nothing to transmit. Thus, Synchronous Time Division Multiplexing is used to provide constant time delay. It can also provide constant bandwidth.

10. Time Division Multiplexing  is based on orthogonality.

a) True

b) False

Answer: a

Explanation: Both Frequency Division Multiplexing  and Time Division Multiplexing  are based on orthogonal multiplexing. Orthogonal multiplexing is a method of encoding digital data on multiple carrier frequencies.

11. As distance increases ________

a) Packet size also increases

b) Packet size decreases

c) Packet size becomes twice of its previous value

d) Packet size becomes half

Answer: a

Explanation: Distance is directly proportional to packet size. So as distance increases packet size also increases.

12. If 32 equally probable events exists and we have to select one of them, number of required bits is?

a) 2

b) 4

c) 8

d) 5

Answer: d

Explanation: 2 5 = 32, so number of bits required is 5.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Methods of Reducing Distortion”.

1. Quantization error occurs in ________

a) Time Division Multiplexing

b) Frequency Division Multiplexing

c) Pulse Code Modulation

d) Pulse Width Modulation

Answer: c

Explanation: The difference between an input value and its quantized value is called quantization error or we can also see it as that when an analog number is not converted into an exact digital number. It takes place in pulse code modulation . Pulse Code Modulation is a technique in which the amplitude of an analog signal is converted to a binary value represented as a series of pulses.

2. If power transmitted is 90kW, what is the field at a distance of 45km?

a) 2

b) 1

c) 0.036

d) 0.01

Answer: c

Explanation: Electric Field a region around a charged particle or object within which a force would be exerted on other charged particles or objects.

analog-communications-questions-answers-methods-reducing-distortion-q2

3. Find the number of pulses, if the number of quantization levels is 32 in PCM?

a) 3

b) 6

c) 4

d) 5

Answer: d

Explanation: Quantization is a process in which the continuous range of values of an analog signal is sampled and divided into non-overlapping  subranges, and a discrete, unique value is assigned to each sub-range.

Therefore, number of pulse in quantisation level = 2 n = 32, so n = 5, where n = Quantization Level.

4. Which transistor amplifier is most commonly used?

a) Common Base

b) Common Emitter

c) Common Collector

d) None of these

Answer: b

Explanation: Common Emitter is most widely used because it has high power gain and voltage gain. In this method of connection, small changes in base/emitter current cause large changes in collector/emitter current. Therefore, the circuit is that of a current amplifier. Moreover, it also provides maximum transconductance for a given load.

5. A device uses a 8 bit word then the maximum number of words it can transmit is ________

a) 64

b) 256

c) 1024

d) 512

Answer: b

Explanation: Maximum number of words which an n-bit device can transmit = 2 n

Therefore, when n = 8,

Number of words it can transmit is 2 8 = 256.

6. Peak voltage of a carrier is 8kV, each sideband has an amplitude of 800V. Find its modulation index?

a) 0.28

b) 0.09

c) 0.02

d) 0.08

Answer: c

Explanation: (mP c )/2 = P sb , where m = Modulation Index, P c = Carrier Power and,

P sb = Power of each sideband

Therefore, (mV c 2 )/2 = V sb 2 2 (V c = 8000 V, and V sb = 800)

Therefore, m = (800 2 X 2) / 8000 2 = 0.02.

7. What do you understand by the term Cross talk?

a) generation of closely lying sidebands

b) a method of increasing bandwidth

c) a method of decreasing bandwidth by converting DSB-SC signal to SSB-SC

d) disturbance caused in nearby circuit due to transmitted signal

Answer: d

Explanation: Crosstalk is a disturbance caused by the electric or magnetic fields of one telecommunication signal affecting a signal in an adjacent circuit. It is generally caused by undesired coupling. In a telephone circuit, crosstalk can result in the hearing part of a voice conversation from another circuit.

8. AM waves is represented by E t cos ⁡ω c t. What does E t denotes?

a) envelope

b) carrier signal

c) modulating signal

d) amplitude

Answer: a

Explanation: AM wave is represented by (A + x t ) cos⁡ω c t or E t cos⁡ω c t, where x t is modulating signal, A is amplitude and therefore, E t is the envelope of the AM wave.

9. Wireless communication takes place through ________

a) EM waves

b) X-Rays

c) Optical Fibres

d) Infrared Waves

Answer: a

Explanation: Wireless communication takes place through electromagnetic waves. Waves are transmitted through an antenna.

10. Which modulation technique uses minimum bandwidth?

a) DSB-SC

b) SSB-SC

c) FM

d) VSB

Answer: b

Explanation: SSB-SC modulation technique uses minimum bandwidth as it suppresses the carrier and transmits either of the two side-bands while DSB-SC suppresses the carrier and transmits both the side-bands.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Power Calculation”.

1. If peak voltage of a carrier wave is 10V, what is the peak voltage of modulating signal if modulation index is 50%?

a) 10V

b) 20V

c) 8V

d) 5V

Answer: d

Explanation: From the relation, Modulation Index µ = V m /V c = 50% = 0.5,

where V m = Peak voltage of modulating signal,

V c = Peak voltage of a carrier wave = 10V,

Therefore, V m = 10 X 0.5 = 5V.

2. Maximum Amplitude of an amplitude modulated 10V and minimum amplitude is 5V. Find its modulation index?

a) 0.65

b) 0.9

c) 0.33

d) 1

Answer: c

Explanation: We know, Modulation Indexµ = (V max -V min )/(V max +V min ),

Where, V max = Maximum Amplitude of an amplitude modulated = 10V

V min = Minimum amplitude of an amplitude modulated = 5V

Therefore, µ = / = 0.33.

3. 24 channels, each band limited to 3.4 KHz, are to be time division multiplexed. Find the bandwidth required for 128 quantization level? 

a) 2436 KHz

b) 1002 KHz

c) 1536 KHz

d) 1337 KHz

Answer: c

Explanation: N = 24, f m = 3.4 kHz

m = 128,

2 n = m = 128, n = 7

But f s = 2f m , where, f s = sampling frequency

instead at 2f m 2 x 3.4 kHz 6.8 KHz.

B.W. = NX f s = [24] 8 kHz = 1536 KHz.

4. Sampling frequency of a signal is 6 KHz and is quantized using 7 bit quantizer. Find its bit rate?

a) 48kbPs

b) 64kbPs

c) 16kbPs

d) 8kbPs

Answer: a

Explanation: Bit rate refers to the rate at which data is processed or transferred. It is usually measured in seconds, ranging from bps for smaller values to kbps and mbps.

Bit rate is also known as bitrate or data rate.

Bit rate, R b = 1 ⁄ T b where analog-communications-questions-answers-power-calculation-q4 where n = number of bits and f s = Sampling Frequency

T b = 1/42, therefore Bit rate = 42 Kbps.

5. Calculate power in each sideband, if power of carrier wave is 96W and there is 40% modulation in amplitude modulated signal?

a) 11.84W

b) 6.84W

c) 3.84W

d) 15.84W

Answer: c

Explanation: Modulation index = 0.4 and Pc = 96W. Power in sidebands may be calculated as analog-communications-questions-answers-power-calculation-q5

6. For 50% modulation, power in each sideband is ________ of that of carrier.

a) 10%

b) 4.32%

c) 5%

d) 6.25%

Answer: d

Explanation: Modulation index = 0.5. Power in sidebands may be calculated as analog-communications-questions-answers-power-calculation-q6

7. For 100% modulation, total power is ________

a) 1.5P c

b) 2P c

c) 3.75P c

d) 1.25P c

Answer: a

Explanation: Total power, P t = P c (1 + µ 2 ⁄ 2 ), where P c = Carrier Power

where µ = 1 ,

so P t = P c (1 +(1 2 /2)). On solving it we get P t = 1.5P c .

8. If each element of signal occupies 70ms, what will its speed?

a) 11.23 bauds

b) 14.28 bauds

c) 17.39 bauds

d) 13.33 bauds

Answer: b

Explanation: The carrier signal is characterized by the number of signal intervals, or pulses, that are transmitted per second. Each pulse is called a baud. Bps stands for bits per second. Bps is a measure of how many bits can be transmitted during one pulse .

analog-communications-questions-answers-power-calculation-q8

9. Power of carrier wave is 300W and modulation index is 0.75. Find its total power?

a) 465W

b) 384W

c) 323W

d) 502W

Answer: b

Explanation: Total power, P t = P c (1 + µ 2 ⁄ 2 ), where P c = Carrier Power = 300W

where Modulation Index µ = 0.75,

So P t , analog-communications-questions-answers-power-calculation-q9

10. If a wave is modulated by two waves. One of them has modulation index equal to 0.75 and other has 0.2, the total modulation index will be ________

a) 0.67

b) 0.58

c) 0.77

d) 0.35

Answer: c

Explanation: Given that m1 = 0.75 and m2 = 0.2. Total modulation index will be equal to analog-communications-questions-answers-power-calculation-q10 By substituting values we have analog-communications-questions-answers-power-calculation-q10a which is equal to 0.77.

11. Find the power saving for DSB-SC wave with 100% modulation?

a) 66%

b) 86%

c) 50%

d) 33%

Answer: a

Explanation: In DSB-SC carrier is suppressed.

So Total Power required in DSBSC Modulation = (u 2 XP c )/2 = P c /2

In normal AM, carrier is not suppressed.

So total power required in AM Modulation = (1+(u 2 /2))XP c = 3P c /2

Therefore, Power saving = ((P c /2)/(3P c /2)) x 100% = 66%.

12. If power transmitted is 45kW, field at a distance of 23km will be ________

a) 0.02

b) 0.75

c) 0.05

d) 0.03

Answer: c

Explanation: Field is a region around a charged particle or object within which a force would be exerted on other charged particles or objects.

analog-communications-questions-answers-power-calculation-q12

13. Find the number of pulses, if the number of level is 128 in PCM?

a) 3

b) 6

c) 4

d) 7

Answer: d

Explanation: A pulse in signal processing is a rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value.

Therefore,

2 n = 128, so n = 7.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Spectrum of Multitone Signal”.

1. Video signals are transmitted through ________

a) Frequency Modulation

b) Amplitude Modulation

c) Pulse Modulation

d) Either frequency or amplitude modulation

Answer: b

Explanation: Video signals require a large transmission bandwidth for transmission. So modulation of video signals is possible only by amplitude modulation. It is executed using Vestigial Sideband modulation, where either of the two sidebands is fully transmitted and the other sideband is partly transmitted.

2. What you understand by the term discone antenna?

a) combination of disc and cone

b) combination of disc and cone with a spacing of ʎ/4

c) combination of disc and cone with a spacing of ʎ/2

d) same as a simple antenna

Answer: a

Explanation: Discone antenna is a combination of disc and cone. A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath. It is usually vertically mounted, with disc at top and the cone beneath.

3. A system has a voltage of 15V and it produces a total current of 1300μA. Find the power of system?

a) 0.025W

b) 0.035W

c) 0.0195W

d) 0.045W

Answer: c

Explanation: Electrical power is the rate at which electrical energy is converted to another form, such as motion, heat, or an electromagnetic field.

Power, P = 15 x 1300 x 10 -6 = 0.0195W.

4. An input resistance of 20 Kῼ causes a noise voltage of 10μV. Suppose two input resistance each of 20 Kῼ are connected in parallel, then find the total noise voltage?

a) 8μV

b) 10μV

c) 20μV

d) 13μV

Answer: a

Explanation: Thermal noise is distinct from shotnoise, which consists of additional current fluctuations that occur when a voltage is applied and a macroscopic current starts to flow. analog-communications-questions-answers-spectrum-multitone-signal-q4

5. Modem is combination of both modulator and demodulator.

a) True

b) False

Answer: a

Explanation: A modem  is used to modulate one or more message signals using one or more carrier waves on the transmitting side. It also demodulates the received encoded signal to get the original information signal.

6. Any signal and its Hilbert transform are mutually orthogonal.

a) True

b) False

Answer: a

Explanation: Hilbert Transform of any signal produces a signal which has same amplitude as that of the original signal but suffers a phase-shift of -90 degree. Consider f be any signal and f h  is it’s Hilbert transform.

If we integrate both of them under proper boundary conditions, we get 0 which shows that both are mutually perpendicular i.e.

analog-communications-questions-answers-spectrum-multitone-signal-q6

7. What Squelch circuit does?

a) helps to receive signals that are useful for the system

b) helps to make channel noise free

c) helps to receive two or more than two signals at once

d) helps to suppress the audio output in the absence of sufficiently strong desired signal

Answer: d

Explanation: A Squelch is a circuit which is a mean to impede, but not destroy a signal. It circuit blocks the output in the absence of sufficiently strong desired signal. It is widely used in two-way radios to suppress the annoying sounds.

8. Mostly used radio receivers are?

a) pulsed receivers

b) CW receivers

c) TRF receivers

d) super heterodyne receivers

Answer: d

Explanation: Superheterodyne Receivers are radio receivers that use frequency mixing to convert a received high frequency signal to a fixed lower intermediate frequency which can be processed more conveniently. It is also the most used receivers. It is used in a variety of applications from broadcast receivers to two-way radio communication links as well as many mobile radio communications systems.

9. Find the step size of a signal with peak to peak amplitude of 4V and is quantized into 64 levels?

a) 32.3 x 10 -3

b) 30.23 x 10 -3

c) 62.5 x 10 -3

d) 53.3 x 10 -3

Answer: c

Explanation: Step size is the voltage difference between one digital level  and the next one . Quantization step size is the smallest possible difference in amplitude.

Therefore,

Step size, analog-communications-questions-answers-spectrum-multitone-signal-q9

10. If the step size of a system is 0.0625, find its quantization power?

a) 3.25 x 10 -3

b) 3.25 x 10 -4

c) 3.25 x 10 -2

d) 3.25 x 10 -1

Answer: b

Explanation: Quantization noise is a model of quantization error introduced by quantization in the analog-to-digital conversion  in telecommunication systems and signal processing. It is a rounding error between the analog input voltage to the ADC and the output digitized value.

Therefore, analog-communications-questions-answers-spectrum-multitone-signal-q10

This set of Analog Communications Interview Questions and Answers focuses on “Modulation Using Non-Linear Devices ”.

1. The approximate aspect ratio for television is ________

a) 2 : 1

b) 3 : 2

c) 4 : 3

d) 3 : 4

Answer: c

Explanation: Aspect ratio is an image projection attribute that describes the proportional relationship between the width of an image and its height. The most common video-graphic aspect ratio is 4:3.

2. Signal to Noise ratio for a hi-fi system is equal to ________

a) 50 dB

b) 100 dB

c) 75 dB

d) 10 dB

Answer: a

Explanation: Signal to Noise ratio compares signal power to noise power. It determines how much signal is present in a transmitted wave compared to presence of noise. It is generally expressed in decibels. For a hi-fi system, it should be equal to 50dB.

3. What is the use of SSB?

a) It has lesser bandwidth

b) It has large bandwidth

c) It has infinite bandwidth

d) It has zero bandwidth

Answer: a

Explanation: In SSB-SC, the carrier is suppressed and either of the upper side-band and lower-sideband, are transmitted. This reduces it’s bandwidth to the frequency of the message signal.

4. Approximate how many times odd and even fields of television system are scanned?

a) 25 times each

b) 50 times each

c) 50 times each but alternately

d) 25 times each but alternately

Answer: d

Explanation: In television system in India, each of odd and even fields are scanned 25 times but alternately.

5. Any signal and its Hilbert transform have same energy density spectrum.

a) True

b) False

Answer: a

Explanation: Hilbert transform of a signal results in a signal with same amplitude but a phase shift of -90 degrees. Thus, a signal and it’s Hilbert transform have same amplitude spectrum i.e. they have same energy density spectrum and also correlation spectrum.

6. If the spectrum of a narrow band noise is symmetrical and it has a power density spectrum 4×10-6. Power density of quadrature component is ________

a) 2 x 10 -6

b) 5 x 10 -6

c) 3 x 10 -6

d) 4 x 10 -6

Answer: a

Explanation: Power density is the amount of power per unit volume. Quadrature component is a amplitude modulated sinusoid which is offset in phase by one quarter cycle.

Power density of quadrature component is analog-communications-interview-questions-answers-q6

7. What is the capacitive reactance for DC signals?

a) zero

b) very low

c) equal to one

d) infinite

Answer: d

Explanation: Frequency of DC signals is zero. For zero frequency, capacitive reactance X C is infinite as X C = 1/, where f is the frequency and C is the capacitance.

8. If a FM signal having modulation index m f is passed through a frequency tripler, then the modulation index of output of frequency tripler is ________

a) m f

b) 3m f

c) 1 ⁄ 3 m f

d) 1 ⁄ 9 m f

Answer: b

Explanation: A frequency tripler is a frequency multiplier in which an electronic circuit generates an output signal whose output frequency is a harmonic  of its input frequency. When a FM signal is passed through a frequency tripler, it increases its modulation index 3 times. So the modulation index of output is 3m f .

9. What are the two major drawbacks of delta modulation?

a) Slope Overload and Granular noise

b) Slope Overload and Serration noise

c) Serration noise and Granular noise

d) Slope Overload and Channel Noise

Answer: a

Explanation: Delta modulation is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance. It is the simplest form of differential pulse-code modulation  where the difference between successive samples are encoded into n-bit data streams. The two major drawbacks in delta modulation are slope overload and granular noise. When step size becomes too small to track the original waveform it generates an error known as slope overload and granularity occurs when step size is too large.

10. Beam width of antenna is expressed in ________

a) metres

b) degrees

c) radian

d) volt

Answer: b

Explanation: Angular separation between the two half-power  points is known as beam width. It is usually expressed in degrees.

This set of Analog Communications Questions and Answers for Entrance exams focuses on “Generation of AM Using Amplifiers”.

1. Consider a wave, v = 15 sin , what is the carrier and signal frequency?

a) 2.5Hz and 200Hz

b) 1.5Hz and 100Hz

c) 1.5Hz and 207Hz

d) 5.5Hz and 500Hz

Answer: c

Explanation: Comparing with the general FM equation,

FM = A c sin(2πf c t + βsin(2πf m t)),

Therefore,

Signal and Carrier frequency are respectively analog-communications-questions-answers-entrance-exams-q2

2. SWR is 1 for ________

a) Open or Short Circuit

b) Open circuit only

c) Short circuit only

d) Series or Parallel Circuit

Answer: a

Explanation: Standing Wave Ratio  is defined as the ratio of the maximum radio-frequency  voltage to the minimum RF voltage along the line. If the line is open or short circuited, SWR is always 1.

3. The resonance frequency of an amplifier is 7MHz and it is having a bandwidth of 10KHz. What is its Q factor?

a) 7000

b) 70

c) 700

d) 7

Answer: c

Explanation: Q factor = Frequency/Bandwidth

= 7MHz/10KHz = 700.

4. Which chart is used for calculations of transmission lines?

a) Andre chart

b) Smith chart

c) Wilson chart

d) Federer chart

Answer: b

Explanation: Smith chart is highly used in radio frequency engineering. Because it is highly useful in solving problems related with transmission lines and matching circuits. It is highly useful for displaying multiple parameters like impedance, admittance etc simultaneously.

5. What is the effective power if the transmitted power of 5W is increased to 50dB?

a) 100KW

b) 300KW

c) 500KW

d) 700KW

Answer: c

Explanation: According to given problem, 10log 10 (P/P t ) = 50,

10log 10  = 50.

So, P = 500KW.

Where, P = Effective Power, P t = Transmitted Power.

6. Field intensity follows ________

a) Bragg’s law

b) Inverse square law

c) Coulomb’s law

d) Gauss’s law

Answer: b

Explanation: Strength of an electric field due to a charge Q is inversely proportional to the square of the distance from the source. In electrostatics, inverse square law is also known as Coulomb’s Law.

7. If the power density at a given distance ‘R’ is one microwatt per square meter and the effective area of antenna is one square meter then the power captured by antenna is one microwatt.

a) True

b) False

Answer: a

Explanation: The above statement is true because power density is equal to analog-communications-questions-answers-entrance-exams-q8

where,

Power Density = 1 mW

P t = Power captured by antenna,

Area of antenna = 4πR 2 = 1m 2 .

8. The gain of antenna  is the ratio of power radiated in a particular direction to the power radiated from an isotropic antenna.

a) True

b) False

Answer: a

Explanation: Gain of antenna,

analog-communications-questions-answers-entrance-exams-q9

9. EM waves are attenuated as they travel.

a) True

b) False

Answer: a

Explanation: Electromagnetic radiation can travel through many forms of medium. They travel at the speed of light in air or free space, which are ideal media. However conductive media like metals form a barrier through which they do not travel. There are also some media through which when they travel, get attenuated. EM waves are attenuated as they travel because both field and power decrease as distance increases.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Envelope Detector”.

1. Envelope Detector is a/an ________

a) Coherent detector

b) Asynchronous Detector

c) Synchronous Detector

d) Product Demodulator

Answer: b

Explanation: An envelope detector is used to demodulate a previously modulated signal by removing all high frequency components of the signal. The capacitor and resistor form a low-pass filter to filter out the carrier frequency. Envelope detectors are asynchronous in nature. The advantage of asynchronous over synchronous is that it is simple, cheap and setup is faster.

2. Effective radiated power  is equal to ________

a) P t ×G t ×P d

b) P t ×P d

c) G t ×P d

d) P t ×G t

Answer: d

Explanation: Effective Radiated Power  measures the combination of the power emitted by the transmitter and the ability of the antenna to direct that power in a given direction. Thus, Effective Radiated Power is equal to the product of antenna gain (G t ) and power transmitted (P t ).

3. Power density from an isotropic antenna is equal to ________

a) \

 

 \

 

 \

 

 \(\frac{P_t}{4 \pi R}\)

Answer: a

Explanation: Power of a transmitter that is radiated from an isotropic antenna will have a uniform power density in all direction. An isotropic antenna is an ideal antenna that radiates its power uniformly in all directions. There is no actual physical isotropic antenna. However, an isotropic antenna is often used as a reference antenna for the antenna gain. The power density at any distance ‘R’ for an isotropic antenna is equal to \(\frac{P_t}{4 \pi R^2}\).

4. Compact discs mainly use ________

a) optical recording

b) magnetic recording

c) magnetic retrieval

d) both optical and magnetic recording

Answer: a

Explanation: Compact disk  is mainly used for storage of data. It was developed only for store and play only audio but was later adapted for storage of data also. It mainly used optical recording and retrieval.

5. If the distance between antenna and source doubles, the received signal power decreases by 1 ⁄ 4 .

a) True

b) False

Answer: a

Explanation: It is due to the R 2 term in formula, analog-communications-questions-answers-envelope-detector-q5 . Thus, the received signal power is inversely proportional to the distance between antenna and source.

6. Power density follows inverse square law.

a) True

b) False

Answer: a

Explanation: From the given formula, analog-communications-questions-answers-envelope-detector-q5 With increase in distance, power density decreases. So, we can also say that power density is inversely related to distance. Thus, Power density follows inverse square law.

7. There is no requirement of IF amplifier stages for a video monitor.

a) True

b) False

Answer: a

Explanation: IF amplifiers are used to change the frequency levels in circuits that are too selective, difficult to tune, and unstable. However, Video amplifier is used to amplify video signals before passing them to a Cathode ray tube. And there is no need of IF amplifier stages for a video monitor.

8. Helical antenna is circularly polarized.

a) True

b) False

Answer: a

Explanation: A helical antenna is an antenna consisting of one or more conducting wires  wound in the form of a helix. In helical antenna, polarization is equally divided between vertical and horizontal components and thus it is circularly polarized.

9. The intermediate frequency of a superheterodyne receiver is 500KHz. What is the image frequency at 1200KHz?

a) 600KHz

b) 500KHz

c) 700KHz

d) 200KHz

Answer: c

Explanation: The image frequency is an undesired input frequency which is demodulated by superheterodyne receivers along with the desired incoming signal. This results in two stations being received at the same time, thus producing interference. In the given problem, Image frequency is equal to  which is equal to 700KHz.

10. Which of these amplifiers is used for impedance matching?

a) Common Base

b) Common Emitter

c) Common Collector

d) Common Base & Emitter

Answer: c

Explanation: An amplifier is an electronic circuit that is used to amplify the voltage signal or a current signal. Output impedance of common collector amplifier is low and thus it is suitable for impedance matching.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Linear Modulation”.

1. Discone antenna is mainly used in UHF range.

a) True

b) False

Answer: a

Explanation: A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath. Discone antenna is a combination of disc and cone. Discone antenna is omnidirectional so it is mainly used in UHF range. It is especially used in airports.

2. Squelch circuit is normally inserted in receiver ________

a) after detector

b) before detector

c) before mixer

d) after power amplifier

Answer: a

Explanation: Squelch is a circuit that acts to suppress the audio  output of a receiver in the absence of a sufficiently strong desired input signal. Squelch is added to suppress noise. It is added after detector when there is no carrier.

3. Each frequency gives rise to four side bands.

a) True

b) False

Answer: b

Explanation: Each frequency in communication gives rise to two side bands, Upper Sideband and Lower Sideband.

4. Field strength  is directly proportional to the square of transmission power.

a) True

b) False

Answer: b

Explanation: Field Strength is the intensity of an electric or magnetic field. Actually the Field strength  is directly proportional to the square root of transmission power i.e. E ∝ √P t .

5. If the transmitted power is 100KW then the field at a distance ‘R’ is 60mV/m. Suppose if the transmitted power is reduced to 50KW then the field at same distance ‘R’ will be equal to ________

a) 50mV/m

b) 42mV/m

c) 45mV/m

d) 55mV/m

Answer: b

Explanation: Since, Field strength  is directly proportional to the square root of transmission power i.e. E ∝ √Pt. Therefore analog-communications-questions-answers-linear-modulation-q5 which gives x = 42mV/m

6. If the value of resistor becomes 16 times than its previous value then its noise voltage will become ________

a) 16 times

b) 8 times

c) 4 times

d) 2 times

Answer: c

Explanation: Since the noise voltage is directly proportional to square root of resistance so if the value of resistor increased to 16 times then its noise voltage will become 4 times.

7. What is the modulation index for a single tone modulation, given that positive peak of AM wave is 20V and minimum value is 2V?

a) 0.81

b) 0.91

c) 0.73

d) 1

Answer: a

Explanation: Modulation Index  = /

= / = 9/11 = 0.81.

8. TV remote control used ultra violet light.

a) True

b) False

Answer: b

Explanation: The infrared  and the ultraviolet rays represent the two extremities of the visible spectrum . While IR represents electromagnetic radiation with wavelengths longer than those of visible light, UV represents wavelengths shorter than visible light. Each time we press any button of TV remote, it sends a beam of infrared rays. For different commands, it sends out different beams that are detected by a microchip lying inside TV.

9. How capacitance is related to thickness?

a) it is inversely proportional to thickness

b) it is directly proportional to thickness

c) it is inversely proportional to twice of thickness

d) it is directly proportional to twice of thickness

Answer: a

Explanation: The thickness of capacitor affects the value of capacitance because capacitance is dependent on structure and distance between two plates.

Thus, Capacitance, C = A×∈ ⁄ t so it is inversely proportional to thickness.

10. Noise gets mixed with signal at ________

a) receiver

b) transmitter

c) transducer

d) channel

Answer: d

Explanation: Channel acts as a path for taking signals to the receiver. It is a medium of transmission of data from source to destination. There is a high probability of involving noise at the channel.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Average Power For Sinusoidal AM”.

1. A 1000KHz carrier is modulated by 100Hz and 200Hz waves, then which of the following frequencies cannot be present at the output?

a) 1000.1KHz

b) 999.9KHz

c) 1000.2KHz

d) 999.7KHz

Answer: d

Explanation: Frequencies present at output will be 1000 ± 0.1 KHz = 1000.1KHZ and 999.9KHz and 1000 ± 0.2 KHz = 1000.2KHZ and 999.8KHz. Therefore, Only, 999.7KHz is out of the range.

2. Aspect ratio is the ratio of ________

a) width to height

b) height to width

c) power to width

d) width to power

Answer: a

Explanation: Aspect ratio, being one of the crucial attributes in image projection, describes the varying relationship between the width of the image and it’s height. Thus, Aspect ratio is the ratio of width to the height of image .

3. If the levels in PCM are transmitted in 10 unit code having sampling frequency equals to 20KHz. What is its bandwidth?

a) 150KHz

b) 125KHz

c) 100KHz

d) 110KHz

Answer: c

Explanation: PCM bandwidth is half of Bit rate.

Bit Rate = 10 X 20 = 200

Bandwidth = 200/2 = 100 KHz.

4. Carrier frequency is given by the formula ________

a) \

 

 \

 

 \

 

 \(\frac{1}{\pi \sqrt{LC}}\)

Answer: a

Explanation: Carrier wave is a high frequency signal whose certain characteristics, like amplitude, phase and frequency, are varied with respect to the instantaneous amplitude of the baseband signal . This variation is called modulation. Carrier frequency is given by the formula, f c = \(\frac{1}{2 \pi \sqrt{LC}}\) where L is inductance and C is Capacitance.

5. Among all amplifiers, Common Collector has highest power gain.

a) True

b) False

Answer: b

Explanation: An amplifier is an electronic device that increases the voltage, current, or power of a signal. Amplifiers are used in wireless communications and broadcasting, and in audio equipment of all kinds. It is common emitter which has highest power gain. Common emitter has a very high voltage gain and also has good amount of current, so its power gain is high.

6. Find the carrier frequency if the inductance and capacitance are 30μH and 10nF respectively?

a) 244KHz

b) 523KHz

c) 290KHZ

d) 300KHz

Answer: c

Explanation: Carrier frequency is a waveform  that is modulated  with an input signal for the purpose of conveying information. analog-communications-questions-answers-average-power-sinusoidal-am-q6

7. Helical antenna is used to obtain ________ polarization.

a) elliptical

b) circular

c) linear

d) perpendicular

Answer: b

Explanation: A helical antenna is an antenna made of one or more conducting wires wound in the form of a helix. It produces circular polarization, because of which it is highly used in radio telemetry.

8. What is number of possible outputs if there is 6 line digital input?

a) 64

b) 32

c) 16

d) 128

Answer: a

Explanation: Total possible outputs will be 2 n = 2 6 which is equal to 64.

9. Push pull amplifier is a class B amplifier.

a) True

b) False

Answer: a

Explanation: A push pull amplifier is an amplifier which has an output stage that can drive a current in either direction through through the load. Push pull amplifier uses a pair of active devices that alternately supply current to a connected load and also absorb current from a connected load. It is a class B amplifier.

10. For removing unwanted signals we should use ________

a) mixing method

b) filter method

c) modulation method

d) detecting method

Answer: b

Explanation: Filteration method is used to remove unwanted components from the signal. It is mainly used to eliminate noise.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Time Domain Description”.

1. Distance between direct broadcasting satellite and earth’s surface is ________

a) 4500km

b) 33000km

c) 5200km

d) 36000km

Answer: d

Explanation: Satellite broadcasting takes place between directional parabolic antennae, where the signal is sent via cable to antennae which beams it to the satellite and then the satellite sends back a signal to another location on Earth. A communication satellite amplifies radio telecommunications signals with the help of a transponder. The distance between it and earth’s surface is approximately 36000km.

2. UHF stands for ________

a) Ultra High Electric Field

b) Ultraviolet High Frequency

c) Ultra High Frequency

d) Ultra High Magnetic Field

Answer: c

Explanation: Ultra High Frequency  are frequencies at ultra high levels, thus consisting of radio frequencies in the range of 300 MHz and 3 GHz. Rest of the options don’t have any existence.

3. What is the ITU designation range for VHF?

a) 30 to 300 Kilohertz

b) 300 to 3000 Kilohertz

c) 30 to 300 Megahertz

d) 3 to 30 Megahertz

Answer: c

Explanation: The VHF  are frequencies in the range of 30 MHz to 300 MHz. Frequencies in the range 30 to 300 Kilohertz belong to LF  range, whereas frequencies in the range 300 to 3000 Kilohertz belong to MF  range. Frequencies in the range 3 to 30 Megahertz belong to HF  range.

4. Effective noise at high frequencies is ________

a) Johnson noise

b) Flicker noise

c) transit-time noise

d) Partition noise

Answer: c

Explanation: Transit-time noise is alike to shot noise, and results if the time taken by electrons to reach from emitter to collector is comparable to the period of signals being amplified. Thus, transit-time noise occurs at high frequencies, whereas Flicker noise occurs below a few kilohertz and Johnson noise, also known as thermal noise, occurs at all frequencies.

5. VHF stands for ________

a) very high frequency

b) very high electric field

c) very high magnetic field

d) very high electromagnetic field

Answer: a

Explanation: The VHF  are frequencies in the range of 30 MHz to 300 MHz. Rest options don’t have any existence.

6. Which among the following is the Analog Continuous Modulation technique?

a) PAM

b) PCM

c) AM

d) PM

Answer: c

Explanation: Only AM  is Analog Continuous Modulation technique while rest are Digital Modulation techniques. In AM, the amplitude of a carrier wave is varied with respect to the instantaneous amplitude of the message signal. This is how amplitude modulation takes place.

7. ITU stands for ________

a) Indian Telecommunication Union

b) Indian Telephonic Union

c) International Telephonic Union

d) International Telecommunication Union

Answer: d

Explanation: The International Telecommunication Union  is an United Nations agency serving to correlate all operations regarding telecommunication and provide services all over the world. Rest options are all invalid.

8. If AM transmitter has low level modulation then it has ________

a) high efficiency

b) poor efficiency

c) high modulating power

d) high resistance towards noise

Answer: b

Explanation: In low-level modulation, the generated amplitude modulated signal utilizes less power, followed by the AM signal being amplified by a chain of linear amplifiers. However, in high power applications, the amplifiers that follow the modulator stage will be linear amplifiers which will render the whole modulation as inefficient.

9. Radiation resistance of an antenna is ________

a) a dc resistance

b) an ac resistance

c) a constant value

d) neither ac nor dc resistance

Answer: b

Explanation: Radiation resistance is that part of an antenna that is caused by the radiation of electromagnetic waves from the antenna. It is considered to be an equivalent resistance dissipating the same amount of power as an actual antenna would have radiated. Radiation resistance of an antenna is usually an ac resistance.

10. What do you understand by isotropic antenna?

a) it radiates its power uniformly in all directions

b) it radiates its power non-uniformly in all directions

c) it radiates its power specifically in one direction only

d) it does not radiate any power

Answer: a

Explanation: An isotropic antenna is considered to be an ideal antenna that radiates power uniformly in all directions. Generally, this type of antenna does not exist. However, it is often used to determine certain antenna characteristics like antenna gain.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Frequency Domain Representation”.

1. The spectrum of white noise and impulse noise is similar in terms of ________

a) magnitude spectrum

b) phase spectrum

c) both magnitude spectrum and phase spectrum

d) amplitude spectrum

Answer: a

Explanation: White noise is a random signal having equal intensities of different frequencies. Impulse noise is a type of noise consisting of sudden sounds, which includes unwanted and instantaneous signals. Thus, they have only their magnitude in common.

2. The amount of power and bandwidth necessary to be transmitted for a given amount of information are reduced in _________

a) Single Sideband Modulation

b) Double Sideband Modulation

c) Vestigial Sideband Modulation

d) Amplitude Modulation

Answer: a

Explanation: In SSBSC, the carrier is suppressed and only either of the two sidebands is transmitted. This reduces the power consumption and also lessens the bandwidth. While in DSBSC, the carrier is suppressed but both the sidebands are transmitted, whereas in AM, the carrier as well as both the sidebands are transmitted.

3. A long wave AM broadcast transmitter needs _________

a) very small carrier power

b) very large carrier power

c) small carrier power

d) large carrier power

Answer: b

Explanation: In Communication Systems, a transmitter produces radio waves, which are the modulated message signals, and are transmitted via the antennae. These message signals carry information which are modulated using a carrier wave, having frequency higher than the message signal frequency. Thus, for transmitting information to a large distance, it is necessary that a very large carrier wave is used for modulation.

4. In FM, if we decreases modulating frequency then the modulation index ________

a) will increase, if the modulating voltage amplitude increases

b) will decrease, if the modulating voltage amplitude increases

c) will increase, if the modulating voltage amplitude remains constant

d) will decrease, if the modulating voltage amplitude remains constant

Answer: c

Explanation: In frequency modulation, the modulation index is the ratio of frequency deviation to modulating frequency. Therefore, modulation index can be made inversely proportional to the modulating frequency by keeping amplitude constant. Thus, if we decrease modulating frequency then the modulation index will increase, with amplitude remaining constant.

5. Which of the following modulation system is used for video-modulation?

a) DSB-SC

b) SSB-SC

c) VSB

d) FM

Answer: c

Explanation: Vestigial Sideband Modulation  is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. Thus, video signals are transmitted using VSB modulation.

6. In SSB modulation, only a single sideband is transmitted leaving the other sideband and the carrier.

a) True

b) False

Answer: a

Explanation: In SSBSC, the carrier is suppressed and only either of the two sidebands is transmitted. This reduces power consumption and also lessens the bandwidth.

7. For demodulation of PCM, it is first converted into __________

a) PDM

b) PWM

c) PPM

d) PAM

Answer: d

Explanation: Pulse Code Modulation deals with converting an analog signal to a digital signal. During it’s demodulation, the wave to be treated is to be parallel. The series pulse wave signal is then converted into a parallel digital signal using a serial to parallel converter, after which it is further converted into the original analog signal with the help of a decoder or detector.

8. A noise can be represented as superposition of spectral components.

a) True

b) False

Answer: a

Explanation: Noise is any undesirable electrical energy that falls under the passband of the signal. It is a general term for the unwanted signals that gets added to our original signal. It is usually represented as the superposition of spectral components.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Generation of DSBSC Waves”.

1. LCD uses ________

a) sematic crystals

b) twisted nematic crystals

c) nematic crystals

d) cholesteric crystals

Answer: b

Explanation: LCD uses liquid crystal display. It uses twisted nematic crystals which are a type of liquid crystal, consisting of a substance called the nematic. The nematic liquid crystal is placed between two plates of polarized glass.

2. Which of the following stage is present in FM receiver but not in AM receiver?

a) Amplitude limiter

b) Demodulator

c) AM amplifier

d) Mixer

Answer: a

Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude present in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency modulation and not in amplitude modulation.

3. Function of duplexer in a RADAR is to permit the use of same antenna for transmission and reception.

a) True

b) False

Answer: a

Explanation: A duplexer is being an electronic unit, allows bi-directional communication over the same path. The transmitter and receiver can communicate simultaneously. In radar, the duplexer isolates the receiver from the transmitter while allowing them to share a common antenna.

4. Single Sideband Modulation  is generally reserved for point-to-point communication.

a) True

b) False

Answer: a

Explanation: A point-to-point communication refers to bidirectional communication between only one transmitter and one receiver. In SSB-SC modulation technique, the carrier is suppressed and only one of the two side-bands are transmitted. Thus, it reduces power consumption and lessens bandwidth. Thus, it is preferred for point-to-point communication.

5. For an AM transmitter, class C amplifier can be used after the modulation stage.

a) True

b) False

Answer: b

Explanation: In an AM transmitter, the required transmission power is obtained from class C amplifier, as it is a power amplifier, for low-level or high-level modulation. So it is not used after the modulation stage.

6. For which of the modulated system, the linear amplified modulated stage is used?

a) low level amplitude modulated system

b) high level amplitude modulated system

c) high level frequency modulated system

d) low level frequency modulated system

Answer: a

Explanation: In low-level modulation, the generation of amplitude modulated signal takes place at low power levels. The generated AM signal is then amplified using a chain of linear amplifiers, which are required to avoid waveform distortion. Thus, linear amplified modulated stage is used in low level amplitude modulated system.

7. When noise is passed through a narrow band filter, the output of filter should be?

a) triangular

b) square

c) parabolic

d) sinusoidal

Answer: d

Explanation: Narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. It is a combination of band pass and band reject filter. When noise gets passed through it, the output of it should be sinusoidal.

8. A narrow band noise can exist in _________

a) AM only

b) PCM only

c) FM only

d) AM and FM both

Answer: d

Explanation: Narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. It is a combination of band pass and band reject filter. So it can be used in both AM and FM to pass a band of frequencies or to attenuate a band of frequencies.

9. The upper and lower sideband frequencies for 5KHz amplitude modulation with a 30KHz carrier frequency will be?

a) 35KHz and 25KHz

b) 34KHz and 24KHz

c) 25KHz and 35KHz

d) 0.35KHz and 0.25KHz

Answer: a

Explanation: Upper sideband frequency will be  = 35 KHz and Lower sideband frequency will be  = 25 KHz.

10. Phase array radar can track many targets together.

a) True

b) False

Answer: a

Explanation: A phased array radar is an array of radiating elements, with each having a phase-shifter. The phase of the signal being emitted from the radiating element is changed to produce beams, thereby producing constructive or destructive interference for steering the beams in the required direction. Thus, it can track many targets together.

This set of Analog Communications Questions and Answers for Freshers focuses on “Coherent Detection of DSBSC Waves”.

1. Which among the following is the drawback of Pulse Position Modulation ?

a) Synchronization is required between receiver and transmitter

b) Synchronization is not required between receiver and transmitter

c) Amplitude is constant

d) Instantaneous power of PPM modulated signals is constant

Answer: a

Explanation: Pulse Position Modulation  is a type of modulation process in which position of the pulse of the carrier wave is varied with respect to the instantaneous position values of the message signal. In PPM, there is minimum noise interference but the main disadvantage of the PPM modulation technique is that synchronization between transmitter and receiver must be needed.

2. Calculate the Nyquist rate for the signal x = 12cos50πt + 7 cos75π t – 13 cos100πt.

a) 300 Hz

b) 600 Hz

c) 100 Hz

d) 150 Hz

Answer: c

Explanation: On comparing with general Equation, Acosωt and substituting ω = 2×π× f. We have f 1 = 25 Hz, f 2 = 37.5Hz, f 3 = 100π/2π = 50Hz.

Taking the maximum modulating frequency, fmax = 50Hz

Nyquist rate = 2 × fmax = 2 × 50 = 100 Hz.

3. What is the need of doing Pre emphasis?

a) For boosting of modulating signal voltage

b) For boosting of modulating signal frequency

c) For removing amplitude variations due to noise

d) For removing frequency variations

Answer: a

Explanation: Pre-emphasis is vastly applied in communication systems to improve signal strength before transmission. It refers to boosting the amplitudes of the weak modulating voltages for high audio frequencies in the range of 2 to 15KHz.

4. Amount of data transmitted for a given time is called _________

a) Noise

b) Frequency

c) Bandwidth

d) Power

Answer: c

Explanation: Bandwidth is the maximum amount of data transmitted over a particular period of time. It is also defined as the difference of high frequency and low frequency, of a given band.

5. Consider an AM broadcast station that transmits modulating frequencies up to 10kHz. If it transmits a frequency of 1000 kHz. Find its maximum and minimum upper and lower sidebands frequencies and also the total bandwidth?

a) 900 KHz, 820 KHz, 1000 Hz

b) 720 KHz, 650 KHz, 1020 Hz

c) 1010 KHz, 880 KHz, 15000 Hz

d) 1010 KHz, 990 KHz, 20000 Hz

Answer: d

Explanation: Maximum Frequency, f m =  KHz = 1010 KHz.

Minimum Frequency, f l =  KHz = 990 KHz and,

Bandwidth = 2 * Modulating frequency = Maximum Frequency – Minimum Frequency

=  KHz = 20000 Hz.

6. A superheterodyne receiver receives signal within frequency range of 120 to 180 MHz. Then the required Intermediate frequency is _________

a) 30MHz

b) 60MHz

c) 90MHz

d) 50MHz

Answer: a

Explanation:

analog-communications-questions-answers-freshers-q6

7. Carson’s rule is used to calculate ________

a) Bandwidth of FM signal

b) SNR

c) Modulation index of FM signal

d) Figure of merit

Answer: a

Explanation: Carson’s rule states that only   upper and lower sidebands along with the carrier, have significant magnitude and contain 99% of total power. Thus, as per Carson’s rule, required bandwidth is equal to the twice of sum of the maximum frequency deviation (f d ) and the maximum modulating frequency(f m ), B = 2(f d + f m )Hz.

8. What is the bandwidth of a FM wave when maximum allowed deviation is 50KHz and the modulating signal has a frequency of 15KHz?

a) 130 KHz

b) 260 KHz

c) 65 KHz

d) 50 KHz

Answer: a

Explanation: According to Carson s rule, B = 2(f d +f m ) = 2  = 130 KHz.

9. For signal, m = 50cos, the power dissipated by the 20Ω resistor is ________

a) 100W

b) 65W

c) 74.7W

d) 62.5W

Answer: d

Explanation: In angle modulation, the amplitude of carrier remains constant and thus power depends on amplitude only. On Comparing with the equation, m = Acos(ω c t + m f sinω m t). We have A = 50, dissipated power, analog-communications-questions-answers-freshers-q9

10. Signal and its Hilbert transform have ________

a) same energy density spectrum

b) same power

c) a phase difference of 60°

d) a phase difference of 120°

Answer: a

Explanation: Properties of Hilbert transform states that the signal and its Hilbert transform :

i) have same energy density spectrum

ii) are mutually orthogonal

iii) have same auto correlation function

iv) have same magnitude

v) have a phase difference of “-90” degree.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Hilbert Transform”.

1. If a receiver has poor selectivity then it also have poor ________

a) sensitivity

b) blocking of unwanted signals

c) double spotting

d) reception

Answer: b

Explanation: Selectivity is the ability of a radio receiver to reject unwanted signals and allow only the desired signal to pass. Thus, it’s the blocking of unwanted signals. Sensitivity is the ability of a receiver to amplify weak signals to the desired level, whereas reception means to receive a signal.

2. For a large amount of power, a push pull amplifier is designed for operation as ________

a) class C

b) class B

c) class AB

d) class A

Answer: b

Explanation: A push pull amplifier is an amplifier whose output is a cumulative sum of the outputs of the currents produced by the two different stages of the load. It is generally used when a large amount of power is to be consumed. Of all the power amplifiers, only Class B amplifier is capable to produce such large amount of power.

3. In a Vidicon camera tube, the side of target plate facing the light has a coating of antimony trisulphide and the side facing electron gun has a coating of tin oxide.

a) True

b) False

Answer: b

Explanation: A vidicon camera tube is a type of camera having a photoconductive surface within. In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno 2 and the side facing electron gun has a coating of antimony trisulphide.

4. Autocorrelation function of which noise is a constant?

a) white noise

b) shot noise

c) transit time noise

d) extraterrestrial noise

Answer: a

Explanation: White noise is a random signal having equal intensities at different frequencies. The autocorrelation of white noise signal has a straight vertical line at origin and is zero for rest points. Thus the Autocorrelation function of white noise is constant.

5. Thermal noise shot noise and transit time noise is part of internal noise in communication.

a) True

b) False

Answer: a

Explanation: Internal noise in communication is the noise that gets generated within the receiver or communication system, like thermal noise, shot noise, transit time noise, partition noise and such like. External noise is that noise which is generated from an external source, that is not a part of the communication system.

6. In amplitude modulation, magnitude of side bands is 2ma times the carrier amplitude.

a) True

b) False

Answer: b

Explanation: In amplitude modulation, magnitude of side bands is m/2 times the carrier amplitude , where ‘m’ is the modulation index.

7. In frequency modulation, there is a large increase in noise and hence decrease in the signal to noise ratio.

a) True

b) False

Answer: b

Explanation: In communication system, Signal-To-Noise ratio  is a measure of the amount of signal present compared to the surrounding noise. It is the ratio of signal power to noise power. Thus in frequency modulation, there is a large decrease in noise and hence increase in the signal to noise ratio.

8. The output of a battery eliminator is closed to ________

a) 70V DC

b) 70V AC

c) 6V AC

d) 6V DC

Answer: d

Explanation: A battery eliminator is an electronic device which is powered by an external source  such that it converts the source to a particular DC voltage which can be used as power supply for other devices. Its output is approximately 6V.

9. In India, the subcarrier frequency for transmission of color difference signals in television is approximately ________

a) 10.47 MHZ

b) 5.4 MHZ

c) 7.67 MHZ

d) 1.3 MHZ

Answer: d

Explanation: A carrier wave is a signal with a high frequency which is modulated for transmitting the information signal. A subcarrier is a sideband of the carrier wave, which is also modulated to send additional information. In India, the subcarrier frequency for transmission of color difference signals in television is approximately 1.3MHz.

10. The advantage of using mechanical filter in filter system of sideband suppression is good attenuation characteristics.

a) True

b) False

Answer: a

Explanation: The advantage of using mechanical filter in filter system of sideband suppression is smaller size, good band pass, good attenuation characteristics.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Costas Loop”.

1. Costa’s receiver is used for ________

a) coherent detection of AM-SC signal

b) asynchronous detection of AM-SC signal

c) amplification of signal

d) frequency mixing of signal

Answer: a

Explanation: A Costa’s loop is based on phase-locked loop . The circuit recovers carrier frequency from the suppressed-carrier modulated signals like DSBSC and SSBSC and phase modulated signals like FSK and BFSK. It is generally used for coherent detection of AM-SC signal in receivers.

2. Helical antenna is mainly used for ________

a) bandwidth calculation

b) production of video signals

c) radio transmission

d) satellite tracking

Answer: d

Explanation: A helical antenna is made of one or more conducting wires wound in the form of a helix. It is used for the communication  Very High Frequency  signals through the different layers of atmosphere. Thus, it is used in satellite tracking.

3. Sampling frequency of a compact disk is about ________

a) 30 KHz

b) 50 KHz

c) 10 KHz

d) 70 KHz

Answer: c

Explanation: Sampling frequency is the number of samples per second which helps in extracting a discrete-time signal from a continuous-time signal. For a CD, it is about 10 KHz.

4. In frequency modulation, there is a large increase in noise and hence increase in the signal to noise ratio.

a) True

b) False

Answer: b

Explanation: In communication, Signal-To-Noise ratio  is defined as measure of the amount of signal present compared to the surrounding noise. It is the ratio of signal power to noise power. Thus, in frequency modulation, if there is a large decrease in noise, then there will be increase in the signal to noise ratio.

5. Image frequency is given by ________

a) f s + f i

b) f s ± f i

c) f s + 2f i

d) f s ± 2f i

Answer: c

Explanation: In the superheterodyne receiver, during the frequency conversion process, the local oscillator and the mixer often allow an undesired frequency signal, in addition to the incoming frequency signal. This results in the production of image frequency which is equal to the sum of signal frequency and double intermediate frequency.

6. Atmospheric noise, extraterrestrial noise and man-made noise is part of internal noise in communication.

a) True

b) False

Answer: b

Explanation: Atmospheric noise, extraterrestrial noise and man-made noise is part of external noise in communication. External noise are the ones which are produced by external sources, that are not part of the communication system. Internal noise are the ones which are produced by internal components of the communication system.

7. Thermal noise is a synonym of ________

a) Atmospheric noise

b) shot noise

c) Johnson noise

d) transit time noise

Answer: c

Explanation: Thermal noise is a type of internal noise in communication. It is produced due to thermal excitation of the free electrons in the circuit. It is also known as Johnson noise.

8. Distance at which a sky wave is received back on earth ________ with an angle of incidence.

a) increases

b) decreases

c) can be increase or decrease

d) can neither be increase or decrease

Answer: b

Explanation: The distance at which a sky wave is received back on earth is inversely proportional to the angle of incidence. Thus, the distance at which a sky wave is received back on earth decreases with an angle of incidence.

9. In a Vidicon camera tube, both sides of the target plate have the coating of Sno 2 .

a) True

b) False

Answer: b

Explanation: A vidicon camera tube is a type of camera tube having a photoconductive surface within. In Vidicon camera tube, the side of target plate facing the light has a coating of Sno2 and the side facing electron gun has a coating of antimony trisulphide.

10. Ground wave can be used for communication upto ________

a) 5 KHz

b) 12 KHz

c) 16 KHz

d) 25 KHz

Answer: c

Explanation: Ground wave is that wave that reaches a receiver from a transmitter directly without reflecting from ionosphere. It can be used for communication upto 16 KHz.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Problems of DSBSC”.

1. A Marconi antenna has length equal to ________

a) ʎ ⁄ 4

b) ʎ ⁄ 2

c) 1

d) ʎ ⁄ 8

Answer: a

Explanation: Marconi antenna is like a vertical wire having length one fourth of the working wavelength. Thus, it is a quarter-wave monopole antenna. Since, it was invented by Guglielmo Marconi, so it’s also called Marconi Antenna. It requires a ground plane with very good conductivity. Hence it is also called as a grounded antenna.

2. In a Vidicon camera tube, both sides of the target plate have the coating of antimony tri-sulphide.

a) True

b) False

Answer: b

Explanation: A vidicon camera tube is a type of camera having a photoconductive surface within. In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno 2 and the side facing electron gun has a coating of antimony trisulphide.

3. A trigonometric function is a synonym of ________

a) triangular function

b) orthogonal function

c) singular function

d) rectangular function

Answer: a

Explanation: Trigonometric function is the angle expressed as the ratio of two sides of a right-angled triangle that contains the angle. It can also be seen as a synonym of triangular function.

4. White noise is a synonym of ________

a) partition noise

b) shot noise

c) johnson noise

d) transit time noise

Answer: c

Explanation: White noise is an internal noise of communication system having different frequencies present with equal intensities. It can also be called Thermal noise or Johnson noise.

5. Local programmes in a cable TV can be telecast at any frequency.

a) True

b) False

Answer: a

Explanation: There is not a fixed frequency range or bandwidth set for broadcasting of local programs in a cable TV. It can be telecasted at any frequency, depending on the channel of bandwidth available.

6. Minimum viewing angle of resolution of human eye is ________

a) \

ʎ

 

 \

ʎ

 

 \

ʎ

 

 \(\frac{2ʎ}{d}\)

Answer: b

Explanation: Minimum resolution of human eye for clear observation is generally \(\frac{1.22ʎ}{d}\). The diameter of human eye is about 25mm.

7. Power density spectrum of a resistor R can be expressed as ________

a) 2 kTR

b) 1 kTR

c) 0.75 kTR

d) 3 kTR

Answer: a

Explanation: Power Spectral Density is the quantity of power present in a signal in the frequency domain. The Power Density Spectrum of a resistor R can be expressed as 2 kTR where k is Boltzmann’s constant, T is temperature and R is given resistance.

8. VSB is generally used in ________

a) television production

b) radio transmission

c) telephonic conversations

d) long distance conversations

Answer: a

Explanation: Vestigial Sideband Modulation  is a type of amplitude modulation in which the carrier and only one sideband are completely transmitted and the other sideband is partly transmitted. Thus, television production is done using VSB modulation.

9. A helical antenna is used for satellite tracking due to its __________

a) broad bandwidth

b) circular polarization

c) linear polarization

d) good front to back ratio

Answer: d

Explanation: Helical antenna consists conducting wire. These conducting wire is wound around it in the form of helix. It is mainly used for satellite tracking due to its good front to back ratio.

10. What is the typical bandwidth of a 2-wire telephone line?

a) 20 Hz to 6 KHz

b) 300 Hz to 3.4 KHz

c) 20 Hz to 20 KHz

d) 200 Hz to 6.5 KHz

Answer: b

Explanation: A helical antenna is an antenna made of one or more conducting wires wound in the form of a helix. It produces circular polarization, because of which it is highly used in radio telemetry. It is mainly used for satellite tracking due to its good front to back ratio.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Quadrature Carrier Multiplexing”.

1. The output stage in a television transmitter is likely to be ________

a) screen modulated

b) plate modulated

c) rectangular modulated

d) grid modulated

Answer: d

Explanation: We generally use vestigial sideband modulation  for television production as it reduces the required bandwidth. However, the output stage in a television transmitter is generally grid modulated using a Class C amplifier, In grid modulation, the carrier wave to the message signal is provided by the grid circuit of the electron tube.

2. The advantage of using mechanical filter in filter system of sideband suppression is good band pass.

a) True

b) False

Answer: a

Explanation: Generally, the filters have sharp cut-off frequency as a result of which either of the sidebands are not completely suppressed. Thus, the advantage of using mechanical filter in filter system of sideband suppression is smaller size, good band pass and good attenuation characteristics.

3. Television transmission is possible through ________

a) DSB-SC

b) SSB-SC

c) VSB

d) AM

Answer: c

Explanation: We generally use vestigial sideband  for television production. In VSB, one of the sidebands is completely transmitted whereas the other sideband is partly transmitted, along with the carrier. VSB is used as it reduces the required bandwidth to half.

4. The rms value of a thermal noise voltage is proportional to  _______

a) √k

b) k

c) k 2

d) k 1 ⁄ 3

Answer: a

Explanation: Thermal noise is the noise generated in electronic devices at frequencies below a few kilohertz, due to thermal excitation of electrons. The root mean square value of thermal noise is proportional to root k times, where k represents Boltzmann’s constant.

5. For a human eye the minimum viewing angle of resolution should be ʎ ⁄ D where D is iris opening and ʎ is wavelength of light.

a) True

b) False

Answer: b

Explanation: For a human eye the minimum viewing angle of resolution should be 1.22ʎ/D. The diameter of human eye is about 25mm.

6. In amplitude modulation, magnitude of side bands is ________ times the carrier amplitude.

a) ma ⁄ 2

b) 4ma

c) ma

d) 2ma

Answer: b

Explanation: In amplitude modulation, for a good transmission and reception, the magnitude of side bands must be 4ma times the amplitude of carrier wave, .

7. Noises which get generated within the receiver is called ________

a) Internal noise

b) External noise

c) Man-made noise

d) Extraterrestrial noise

Answer: a

Explanation: Internal noise in communication is the noise that gets generated within the receiver or communication system.

8. Autocorrelation function of white noise is ________

a) an impulse function

b) a step function

c) a constant

d) a variable

Answer: c

Explanation: White noise is an internal noise of communication system having different frequencies present with equal intensities. It has a peak only at zero and are zero at all points. Thus, the autocorrelation function of white noise is a constant.

9. In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno 2  and the side facing electron gun has a coating of antimony trisulphide.

a) True

b) False

Answer: a

Explanation: A vidicon camera tube is a type of camera having a photoconductive surface within. In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno 2 and the side facing electron gun has a coating of antimony trisulphide.

10. Marconi antenna ________

a) is a grounded antenna

b) is an ungrounded antenna

c) can either be grounded or ungrounded antenna

d) can neither be grounded nor ungrounded antenna

Answer: a

Explanation: Marconi antenna is like a vertical wire having length one fourth of the working wavelength. Thus, it is a quarter wave monopole antenna. Since it was invented by Guglielmo Marconi, so it’s also called Marconi Antenna. It requires a ground plane with very good conductivity. Hence it is also called as a grounded antenna.

This set of Analog Communications Question Bank focuses on “Carrier Acquisition Techniques in DSB-SC”.

1. Flyback switched mode is used in television because it can supply many voltage outputs.

a) True

b) False

Answer: b

Explanation: In frequency modulation, power is determined from carrier amplitude and as carrier amplitude does not change, thus power remains constant. So if we increase the modulation index, then also it does not affect power and it will remain constant.

2. What will be the effect on power if the modulation index of a frequency modulated signal is increased?

a) increases

b) decreases

c) remains constant

d) first increases and then decreases

Answer: c

Explanation: In frequency modulation, power remains constant. So if we increase the modulation index then also it does not affect power, it will remain constant.

3. The equation 20sin⁡(10 8 t + 3 sin⁡ 10 9 t) represents which modulation?

a) AM

b) DSB-SC

c) PM

d) FM

Answer: d

Explanation: On comparing with the general equation of each modulation, we found that it represents Frequency modulation.

FM  = A c sin (2πf c t + βsin(2πf m t)), where symbols have their usual meaning.

4. Monopole antenna is a type of travelling wave antenna.

a) True

b) False

Answer: b

Explanation: Monopole antenna is a type of wire antenna like Marconi antenna, also known as quarter-wave antenna. Travelling wave antenna makes use of a travelling wave as a radiating guide and they consist of helical antenna, spiral antenna.

5. In which modulation, frequency of carrier signal is varied with the amplitude of modulating signal?

a) FM

b) AM

c) PM

d) VSB

Answer: a

Explanation: In Frequency Modulation, the frequency of carrier wave is varied with the instantaneous amplitude of modulating signal. The general FM modulated expression is :

FM  = A c sin (2πf c t + βsin(2πf m t)), where symbols have their usual meaning.

6. In Phase Modulation the phase of carrier signal is varied.

a) True

b) False

Answer: a

Explanation: In phase modulation, the phase shift of carrier wave is varied with respect to the instantaneous amplitude of modulating signal. The general PM modulated expression is:

PM  = A c sin (2πf c t + βsin(2πf m t)), where symbols have their usual meaning.

7. Power spectral density of thermal noise remains uniform upto frequency ___________

a) 10 15 HZ

b) 10 5 HZ

c) 10 2 HZ

d) 10 13 HZ

Answer: d

Explanation: Power Spectral Density is the quantity of power present in a signal in the frequency domain. Power spectral density of thermal or white noise gets affected when the frequency becomes greater than 10 13 Hz and thus, it remains uniform upto 10 13 Hz.

8. Carrier frequency remains constant in cell communication.

a) True

b) False

Answer: b

Explanation: In cell communication, the carrier frequency does not remain constant. Instead, the carrier frequency get changes continuously with respect to the instantaneous amplitude of the message signal.

9. Waves of which frequency can penetrate the atmosphere?

a) higher than 10 MHz

b) higher than 20 MHz

c) higher than 30 MHz

d) higher than 100 MHz

Answer: c

Explanation: Most Radio Waves penetrate the atmosphere. Thus, any wave having frequency greater than 30 MHz can penetrate the atmosphere. The waves having frequency less than it cannot penetrate the atmosphere and get absorbed into it.

10. Armstrong modulator can only generate FM signal.

a) True

b) False

Answer: b

Explanation: Armstrong Modulator can also generate PM along with FM. So the statement is incorrect. Thus, collectively Armstrong modulator is an Angle Modulator, where the angle of the carrier wave is varied with respect to the instantaneous amplitude of modulating signal.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Demodulation of DSB-SC”.

1. Flyback switched mode is used in television because it does not require a filter choke.

a) True

b) False

Answer: a

Explanation: Flyback switched mode is used in television because it does not require filter choke. It is also cheap as compared to others.

2. Waves of frequency 60MHz can penetrate the atmosphere.

a) True

b) False

Answer: a

Explanation: Most Radio Waves penetrate the atmosphere. Thus, frequencies above 30MHz can penetrate the atmosphere. So 60 MHz can penetrate the atmosphere.

3. Ground wave travels along surface of ground.

a) True

b) False

Answer: a

Explanation: Ground wave propagation occurs in the area between the surface of the Earth and the Ionosphere. The wave travels parallel or along the surface of the ground. It is usually used for transmission of low frequency signals.

4. TM stands for _________

a) Trans positional Modulation

b) Time Multiplexing

c) Transit Modulation

d) Tuned Modulation

Answer: a

Explanation: TM stands for Transpositional Modulation. In TM, the message signal is modulated by inserting inflections in the original waveform. The waveform is modified resulting in a modulated signal where each quarter cycle is transposed in modulation process.

5. In which of the modulation, the waveform is modified resulting in a signal where each quarter cycle is transposed.

a) AM

b) FM

c) PM

d) TM

Answer: d

Explanation: In TM, the message signal is modulated by inserting inflections in the original waveform. The waveform is modified resulting in a modulated signal where each quarter cycle is transposed in modulation process.

6. Which of the following is a reflector antenna?

a) Marconi reflector antenna

b) Corner reflector antenna

c) Helical antenna

d) Bow tie antenna

Answer: b

Explanation: It is corner reflector antenna that comes under reflector antenna. Helical antenna and bow tie antenna comes under travelling wave antenna and log antenna respectively. Marconi reflector antenna comes under grounded antenna.

7. Carbon microphone has a bidirectional feature.

a) True

b) False

Answer: b

Explanation: Carbon microphone does not have a bidirectional feature. It is ribbon microphone that has bidirectional feature.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Single Side Band Transmission”.

1. What do you understand by the term SSB?

a) Suppressed Side Band

b) Single Side Band

c) Suppressed Single Band

d) Selected Single Band

Answer: b

Explanation: SSB stands for Single Side band. In SSB-SC , the carrier is suppressed and only either of the two sidebands is transmitted. This reduces power consumption and also lessens the bandwidth.

2. SSB is a standard form for radio communication.

a) True

b) False

Answer: a

Explanation: SSB stands for Single Side band. In SSB-SC , the carrier is suppressed and only either of the two sidebands is transmitted. Single Side Band can also be seen as a standard form for radio communication. In Single Side Band, carrier wave is suppressed by about 50dB.

3. Ribbon microphone has a bidirectional feature.

a) True

b) False

Answer: a

Explanation: It is correct statement that a ribbon microphone has bidirectional feature. Other microphones such as carbon, condenser etc does not have a bidirectional feature.

4. Antenna can only be used as a transmitter.

a) True

b) False

Answer: b

Explanation: All antennas can be used as transmitter and receiver both. Antenna transmits or receives electromagnetic waves only. Transmitter antenna modulates the message signals and transmits the modulated waves and Receiver antenna receives the modulated wave and demodulates it.

5. TM is a pseudo analog modulation.

a) True

b) False

Answer: a

Explanation: TM stands for Transpositional Modulation. In TM, the message signal is modulated by inserting inflections in the original waveform. The waveform is modified resulting in a modulated. TM is a pseudo analog modulation. In TM carrier also carries a phase variable.

6. What is the full form of PPM?

a) pulse-position modulation

b) position-pulse modulation

c) pulse-pulse modulation

d) position-position modulation

Answer: a

Explanation: PPM is used for both analog and digital signals. In PPM, when a single pulse is transmitted in the allotted time shift, the message bits get encoded. It is mostly used for optical communication such as optic fiber.

7. CVSDM stands for continuously variable slope delta modulation.

a) True

b) False

Answer: a

Explanation: CVSDM stands for continuously variable slope delta modulation. It can also be seen as delta modulation having variable step size. Delta modulation involves analog to digital conversion and vice-versa for the transmission of voice signals.

8. If the target is changing continuously, then the best scanning system for correct tracking is _________

a) monopulse

b) conical

c) lobe switching

d) sequential

Answer: a

Explanation: If the targeting area is changing continuously then it is better to use monopulse scanning system for accurate tracking as it avoids the problems in conical scanning systems, which often arise due to rapid change in signal strength.

9. In NBFM, the modulation index is close to __________

a) 1

b) greater than 1

c) 10

d) infinite

Answer: a

Explanation: In NBFM, the modulation index is less than or close to unity. It is similar to Amplitude modulation except a 180 degree phase shift at the lower sideband.

10. NBFM stands for Narrow Band Frequency Modulation.

a) True

b) False

Answer: a

Explanation: It is a correct statement that NBFM stands for Narrow Band Frequency Modulation. In NBFM, the modulation index is less than or close to unity. It is similar to Amplitude modulation except a 180 degree phase shift at the lower sideband.

This set of Analog Communications Interview Questions and Answers for freshers focuses on “Representation of SSB-SC in Time & Frequency Domain”.

1. Which device is has more chance to be found in SSB transmitter?

a) balanced modulator

b) class A RF amplifier

c) class C audio amplifier

d) class B RF amplifier

Answer: a

Explanation: In SSB-SC transmitter, a balanced modulator is more likely to be found in order to suppress the carrier, after which the result is passed through a band-pass filter in order to transmit the selected sideband.

2. The RF section of radio consists both oscillator and buffer stage.

a) True

b) False

Answer: a

Explanation: RF is an electromagnetic wave frequencies in the range 3 KHz to 300 GHz. RF section of radio consists of oscillator so as to provide the necessary frequency for mixing and it consists of a buffer stage for preventing the damage of signal source.

3. What is the frequency of audio modulation?

a) 10 Hz

b) 20 KHz

c) 30 KHz

d) 40 KHz

Answer: b

Explanation: Audio spectrum ranges from 20Hz to 20KHz and the frequency band for audio modulation ranges from 88MHz to 108 MHZ.

4. In telegraphy we generally use __________

a) Amplitude modulation

b) Frequency modulation

c) Frequency Shift Keying

d) Pulse Code modulation

Answer: c

Explanation: FSK  is a method used to transmit binary data in form of digital signals. It is mainly used for telegraphy. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for the communication between computers and over telephone lines.

5. In FM both the frequency and amplitude of carrier signal is varied in accordance with the instantaneous value of modulating signal.

a) True

b) False

Answer: b

Explanation: In FM, the frequency of the carrier wave is varied with respect to the instantaneous amplitude of the message signal. The general expression for FM is as follows:

FM  = A c sin (2πf c t + βsin(2πf m t)), where symbols have their usual meaning.

6. In the equation, 20cos⁡(10 8 t + 3 sin⁡10 9 t) the modulation index is ________

a) 1

b) 2

c) 3

d) 4

Answer: c

Explanation: The general expression for FM is as follows:

FM  = A c sin (2πf c t + βsin(2πf m t)), where β is the modulation index.

Thus β = 3.

7. Antenna can also be used as a receiver.

a) True

b) False

Answer: a

Explanation: All antennas can be used as transmitter and receiver both. Antenna transmits or receives electromagnetic waves only. Transmitter antenna modulates the message signals and transmits the modulated waves and Receiver antenna receives the modulated wave and demodulates it.

8. What is the advantage of IF modulation?

a) it uses SSB which further reduces its bandwidth

b) modular section and visual exciter can be of any state

c) it cannot be tuned

d) modular section and visual exciter can be solid state devices

Answer: d

Explanation: Advantages of IF modulation is that the modular section and visual exciter can be solid state devices. Its other advantages are it can use VSB filter that can be introduced at low power level. Moreover it is economical.

9. We can use either cone type or horn type loudspeakers in tape recorders.

a) True

b) False

Answer: b

Explanation: In tape recorders, only cone type loudspeakers can be used. It does not work well with horn type loudspeakers.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Method of Generation of SSB-SC”.

1. A duplex arrangement use separate frequencies for transmission.

a) True

b) False

Answer: a

Explanation: In duplex communication, two-way interaction is favourable simultaneously. Thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units.

2. VSB modulation is used in televisions because it avoids phase distortion at low frequencies.

a) True

b) False

Answer: b

Explanation: Vestigial Sideband Modulation  is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. Thus, television production is done using VSB modulation as it reduces bandwidth to half.

3. A cordless telephone that uses separate frequencies for transmission in base and portable units is called _________

a) half duplex

b) duplex

c) simplex

d) one-way communication

Answer: b

Explanation: In duplex communication, two-way interaction is favourable simultaneously. Thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units.

4. Which polarization is used to reduce the depolarization effect on received waves?

a) Circular polarization

b) Linear polarization

c) Atomic polarization

d) Dipolar polarization

Answer: a

Explanation: In circular polarization at each point the electric field of electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate, in a plane perpendicular to the direction of propagation of wave. It is used to reduce depolarization effect on received waves.

5. Circular polarization involves critical alignment between transmitting and receiving antenna.

a) True

b) False

Answer: b

Explanation: In circular polarization at each point the electric field of the electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate, in a plane perpendicular to the direction of propagation of the wave. It is used to reduce depolarization effect on received waves. It does not involve alignment between transmitting and receiving antenna.

6. It is only the reflected color that decided the color of an object.

a) True

b) False

Answer: b

Explanation: Color of any object is decided by the reflected color for opaque object and wavelength transmitted through it for transparent object, while both reflector color and wavelength transmitted are considered for a translucent object.

7. What do you understand by the term “carrier” in modulation?

a) voltage to be transmitted

b) resultant wave

c) voltage for which amplitude, phase or frequency can be varied

d) voltage for which amplitude, phase or frequency remains constant

Answer: c

Explanation: Carrier wave is the wave with frequency higher than the message signal, whose certain characteristics like amplitude, phase or frequency are varied with respect to the instantaneous amplitude of the message signal. Thus forming the modulated wave which is the wave to be transmitted.

8. Carrier wave in modulation is a resultant wave.

a) True

b) False

Answer: b

Explanation: Carrier wave is the wave with frequency higher than the message signal, whose certain characteristics like amplitude, phase or frequency are varied with respect to the instantaneous amplitude of the message signal. Thus forming the modulated wave which is the wave to be transmitted.

9. For a low level AM system, amplifier modulated stage must have _________

a) harmonic devices

b) linear devices

c) non-linear devices

d) class A amplifiers

Answer: b

Explanation: In low-level modulation, the generation of amplitude modulated signal takes place at low power levels. The generated AM signal is then amplified using a chain of linear amplifiers, which are required to avoid waveform distortion. Thus, linear devices are used in low level amplitude modulated system.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Demodulation of SSB-SC”.

1. The disadvantage of FM over AM is that high output power is needed.

a) True

b) False

Answer: b

Explanation: The disadvantage of FM over AM is that in frequency modulation large bandwidth is required. While, in case of advantages, FM is less prone to noise interference and has lower power consumption compared to AM.

2. Which theorem states that a noiseless Gaussian channel has zero capacity?

a) Beckman-Quarles theorem

b) Bell’s theorem

c) Cameron-Martin theorem

d) Shannon-Hartley theorem

Answer: d

Explanation: According to Shannon Hartley theorem, a noiseless channel has infinite capacity.

3. Linear devices are used in __________

a) high level AM modulator

b) low level AM modulator

c) high level FM modulator

d) low level FM modulator

Answer: b

Explanation: In low-level modulation, the generation of amplitude modulated signal takes place at low power levels. The generated AM signal is then amplified using a chain of linear amplifiers, which are required to avoid waveform distortion. Thus, linear devices are used in low level amplitude modulated system.

4. A noiseless Gaussian channel has _____________

a) zero capacity

b) infinite capacity

c) small capacity

d) finite large capacity

Answer: b

Explanation: According to Shannon Hartley theorem, a noiseless channel has infinite capacity.

5. Advantage of high level modulator is that it requires linear amplifiers.

a) True

b) False

Answer: b

Explanation: In high-level modulation, the generation of amplitude modulated signal takes place at high power levels. It has the advantage that linear amplifiers are not required.

6. Carrier wave in modulation is a wave that is to be transmitted.

a) True

b) False

Answer: b

Explanation: Carrier wave is the wave with frequency higher than the message signal, whose certain characteristics like amplitude, phase or frequency are varied with respect to the instantaneous amplitude of the message signal. Thus forming the modulated wave which is the wave to be transmitted.

7. It is only the wavelength that decides the color of an object.

a) True

b) False

Answer: b

Explanation: Color of any object is decided by the reflected color for opaque object and wavelength transmitted through it for transparent object, while both reflector color and wavelength transmitted are considered for a translucent object.

8. Circular polarization is used in discrimination between reception of adjacent beams.

a) True

b) False

Answer: b

Explanation: In circular polarization at each point the electric field of the electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate, in a plane perpendicular to the direction of propagation of wave. It is used to reduce depolarization effect on received waves and not for discrimination between reception of beams.

9. VSB modulation is used in televisions because it results in better reception.

a) True

b) False

Answer: b

Explanation: Vestigial Sideband Modulation  is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. Thus, television production is done using VSB modulation as it reduces bandwidth to half.

10. A cordless telephone that uses separate frequencies for transmission is known as half duplex.

a) True

b) False

Answer: b

Explanation: In duplex communication, two-way interaction is favourable simultaneously. Thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units.

This set of Analog Communications Questions and Answers for Experienced people focuses on “Demodulation of SSB with Large Carrier”.

1. What is the main disadvantage of FM over AM?

a) high modulating power is needed

b) noise is very high for high frequencies

c) high output power is required

d) large bandwidth is required

Answer: d

Explanation: The disadvantage of FM over AM is that in frequency modulation large bandwidth is required. While, in case of advantages, FM is less prone to noise interference and has lower power consumption compared to AM.

2. To prevent over modulation in radio transmitters we use ___________

a) peak clipper

b) oscillator

c) double oscillator

d) filter

Answer: a

Explanation: Clipper is used to prevent the exceeding of output from a predetermined fixed value. It does not distorted the remaining part of the applied waveform.

3. IN EM waves, polarization ___________

a) is always vertical

b) is caused by reflection

c) is due to transverse nature of waves

d) is due to longitudinal nature of waves

Answer: c

Explanation: In electromagnetic waves, polarization is mainly due to the transverse nature of waves only. Transverse nature of electromagnetic waves mean that the electric and magnetic fields are perpendicular to each other as well as perpendicular to the direction of propagation of waves.

4. In FM receiver, role of amplitude limiter is to amplify low frequency signals.

a) True

b) False

Answer: b

Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude present in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency modulation and not in amplitude modulation.

5. In a FM receiver, amplitude limiter ________

a) eliminates any change in amplitude of received FM signals

b) eliminates any change in frequency of received FM signals

c) reduce the amplitude of received signals

d) amplifies low frequency signals

Answer: a

Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude present in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency modulation and not in amplitude modulation.

6. Base modulation is preferred over collector modulation of a class C transistor because of its better efficiency.

a) True

b) False

Answer: b

Explanation: Base modulation is preferred over collector modulation of a class C transistor because low modulating power is required and collector saturation prevents complete modulation of a signal. Generally, Collector modulation has more advantages over Base modulation like high linearity, better collector efficiency and such like.

7. Base modulation is preferred over collector modulation of a class C transistor because it has high power output per transistor.

a) True

b) False

Answer: b

Explanation: Base modulation is preferred over collector modulation of a class C transistor because low modulating power is required and collector saturation prevents complete modulation of a signal. Generally, Collector modulation has more advantages over Base modulation like high linearity, better collector efficiency and such like.

8. What is the standard IF frequency for AM receivers?

a) 100 KHz

b) 455 KHz

c) 1.07 MHz

d) 10.7 MHz

Answer: b

Explanation: In AM receivers, the standard intermediate frequency is approximately 455 KHz.

9. Balanced modulator is used to produce balanced modulation of a carrier wave.

a) True

b) False

Answer: b

Explanation: Balanced modulator is used to produce 100% modulation by suppressing the carrier and passing only the two sidebands.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Applications of SSB”.

1. What is the purpose of peak clipper circuits in radios?

a) prevent overmodulation

b) reduce bandwidth

c) increase bandwidth

d) regulate oscillator input voltage

Answer: a

Explanation: Clipper is used to prevent the output of a circuit from exceeding a predetermined voltage. It does not distorted the remaining part of the applied waveform.

2. In FM receiver, role of amplitude limiter is to reduce the amplitude of signals.

a) True

b) False

Answer: b

Explanation: Role of amplitude limiter in frequency modulation is to eliminate any change in amplitude of received FM signals.

3. Balanced modulator is used to suppress carrier signal to create an SSB or DSB.

a) True

b) False

Answer: b

Explanation: Balanced modulator is used to produce 100% modulation.

4. What is the main function of a balanced modulator?

a) to limit the noise picked by a receiver

b) to produce balanced modulation of a carrier wave

c) to suppress carrier signal

d) to produce 100% modulation

Answer: d

Explanation: For achieving 100% modulation, balanced modulator is mainly used in circuits.

5. For classifying a modem as low speed its data rate is ________

a) upto 100bps

b) upto 200bps

c) upto 400bps

d) upto 600bps

Answer: d

Explanation: According to standard data for modem, if the data rate is upto 600bps then modem is classified as having a low speed.

6. Varacter diode modulator is an indirect way of generating FM.

a) True

b) False

Answer: b

Explanation: Varacter diode modulator is not an indirect way of generating FM. It is a Armstrong modulator which is an indirect way of generating FM.

7. Which of the following is an indirect way of generating FM?

a) By reactance modulator

b) By bipolar transistor

c) By varacter diode

d) By armstrong modulator

Answer: d

Explanation: Armstrong modulator which is the only way for indirect generating of frequency modulation.

8. Convex lens has negative focal power and concave lens have positive focal power.

a) True

b) False

Answer: b

Explanation: Convex lens has positive focal power and concave lens have negative focal power.

9. All lens have positive focal power.

a) True

b) False

Answer: b

Explanation: Convex lens has negative focal power and concave lens have positive focal power.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Frequency Discrimination Method”.

1. FM and PM are two ways of angle modulation.

a) True

b) False

Answer: a

Explanation: In angle modulation, phase or frequency of the carrier wave is varied with respect to the instantaneous amplitude of the message signal. The general expression for FM and PM are as follows:

FM  = A c sin (2πf c t + βsin(2πf m t)),

PM  = A c sin (2πf c t + βcos(2πf m t)), where symbols have their usual meaning.

2. FM transmitting and receiving equipment is __________ as compared to AM equipment.

a) costly

b) cheaper

c) same price

d) not available

Answer: a

Explanation: Frequency transmitting and receiving equipment is generally costly when compared to amplitude modulated equipment.

3. Which one of the following is analog?

a) PCM

b) PWM

c) Delta modulation

d) Differential PCM

Answer: b

Explanation: Frequency transmitting and receiving equipment are generally costly when compared to amplitude modulated equipment, as the power required in FM transmission is less and bandwidth is high. Also, the noise interference is also less in case of FM.

4. Schmitt trigger is used to generate PDM.

a) True

b) False

Answer: b

Explanation: Pulse density modulation  is used to represent an analog signal using a digital signal. For generating PDM, a monostable multi-vibrator is used, which is externally triggered and has only one stable state.

5. Which of the following is used to generate PDM?

a) Monostable multi-vibrator

b) Bistable Multivibrator

c) Either monostable of free running multi-vibrator

d) Astable Multivibrator

Answer: a

Explanation: Pulse density modulation  is used to represent an analog signal using a digital signal. For generating PDM, a monostable multi-vibrator is used, which is externally triggered and has only one stable state.

6. In case of FM, if the modulating frequency is lowered and the modulating voltage remains constant then the amplitude of distant sidebands decreases.

a) True

b) False

Answer: b

Explanation: If the modulating frequency in FM lowered and the modulating voltage remains constant then the amplitude of distant sidebands increases, as the modulating frequency has no role to play in determining the amplitude of the sidebands.

7. Skip distance depends on the time of day and angle of incidence.

a) True

b) False

Answer: a

Explanation: A skip distance is a distance between the point, where the radio waves from a transmitter are transmitted and the point where the waves are received, after having been refracted by different layers of the ionosphere. It basically depends on time of day as well as on angle of incidence.

8. Leak type bias is used in plate modulated amplifier to prevent tuned circuit damping.

a) True

b) False

Answer: b

Explanation: Leak bias is a type of bias in which the input signal draws grid current from a circuit made of resistors and capacitors. Thus, Leak bias is mainly used to prevent excessive grid current in plate modulated amplifiers.

9. For telegraphy pulse code modulation  is widely used.

a) True

b) False

Answer: b

Explanation: FSK  is a method used to transmit binary data in form of digital signals. It is mainly used for telegraphy. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for the communication between computers and over telephone lines.

10. DVD uses a laser beam for recording and video head for playback.

a) True

b) False

Answer: b

Explanation: Digital Versatile Disc  uses a laser beam for both recording and playback.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Singletone SSB Modulation”.

1. PDM can be generated by either free running multi-vibrator or monostable multi-vibrator.

a) True

b) False

Answer: b

Explanation: Pulse density modulation  is used to represent an analog signal using a digital signal. For generating PDM, monostable multi-vibrator is used, which is externally triggered and has only one stable state.

2. In case of FM, if the modulating frequency is lowered and the modulating voltage remains constant then the amplitude of distant sidebands first increases and then decreases.

a) True

b) False

Answer: b

Explanation: If the modulating frequency in FM lowered and the modulating voltage remains constant then the amplitude of distant sidebands increases, as the modulating frequency has no role to play in determining the amplitude of the sidebands.

3. Skip distance depends on the time of day.

a) True

b) False

Answer: b

Explanation: A skip distance is a distance between the point, where the radio waves from a transmitter are transmitted and the point where the waves are received, after having been refracted by different layers of the ionosphere. It basically depends on time of day as well as on angle of incidence.

4. Leak type bias is used in plate modulated amplifier to ________

a) increase bandwidth

b) decrease bandwidth

c) prevent tuning

d) prevent excessive grid current

Answer: d

Explanation: Leak bias is a type of bias in which the input signal draws grid current from a circuit made of resistors and capacitors. Thus, Leak bias is mainly used to prevent excessive grid current in plate modulated amplifiers.

5. Full duplex operation allows transmission in only one direction at the same time.

a) True

b) False

Answer: b

Explanation: Full duplex operations allow simultaneous communication between two points whereas Half Duplex operation allows transmission between two points one at a time.

6. A woofer is connected from the input through a ________

a) high pass filter

b) low pass filter

c) band pass filter

d) band stop filter

Answer: b

Explanation: A woofer is connected from the input through a low pass filter to restrict the high frequencies and only allows the low frequencies to pass through it.

7. Which of the following is used for attenuating high frequencies?

a) shunt resistance

b) shunt inductance

c) series capacitance

d) shunt capacitance

Answer: d

Explanation: Shunt capacitance is used to improve the power factor in the network. It also improves voltage stability. It serves as a low pass filter and thus is used in the communication system for attenuating high frequencies.

8. If the length of antenna is equal to whole wavelength the radiation is zero in all direction.

a) True

b) False

Answer: b

Explanation: If the length of antenna is equal to whole wavelength only the radiations which is at right angles is zero.

9. For getting zero radiation at right angles, length of antenna should be __________

a) ʎ

b) ʎ ⁄ 8

c) ʎ ⁄ 4

d) ʎ ⁄ 5

Answer: a

Explanation: For getting zero radiation at right angles, length of antenna should be equal to the whole wavelength.

10. What is the commercial frequency deviation of frequency modulation?

a) 70 KHz

b) 75 KHz

c) 80 KHz

d) 85 KHz

Answer: b

Explanation: Frequency deviation is the difference between the maximum instantaneous modulated frequency and carrier frequency. Frequencies lying nearly about 75KHz is considered as commercial frequency deviation for frequency modulation.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Filter Method”.

1. In pulse code modulation bandwidth required is low.

a) True

b) False

Answer: b

Explanation: PCM stands for pulse code modulation. In PCM, the amplitude of the analog signal is discritised and converted into digital form for transmission of binary data. PCM usually requires a large bandwidth.

2. How do we eliminate the ghosts in the picture?

a) by using a long transmission line

b) by using a booster

c) by changing the orientation of antenna

d) by twisting the transmission line

Answer: c

Explanation: Change in antenna orientation helps in improving the reception of signals which further removes ghosts in the picture.

3. For getting maximum undistorted transmitted power in a carrier wave, the value of modulation should be _________

a) 1

b) 0.5

c) 0.2

d) 0.8

Answer: a

Explanation: The possible maximum value of modulation can be one. It signifies 100% modulation and thus at this value we have maximum undistorted transmitted power.

4. To avoid fading in communication, broad band antenna is used.

a) True

b) False

Answer: b

Explanation: It is generally observed that a ship to ship communication suffers from fading. This problem can be avoided by using frequency diversity in which the components of a radio wave are received from different channels thus reducing the error that occurs in the transmission of a single frequency component.

5. What is the commercial channel bandwidth in a frequency modulated system?

a) 150 KHz

b) 250 KHz

c) 500 KHz

d) 900 KHz

Answer: a

Explanation: Bandwidth is the band of frequencies present within a given range of frequency. The standard commercial channel bandwidth for frequency modulated system is about 150 KHz.

6. A buffer amplifier is a ________

a) double tuned amplifier

b) tuned amplifier

c) high gain DC amplifier

d) low gain DC amplifier

Answer: c

Explanation: Gain of an amplifier is its ability to increase the voltage at the input and produce the result at the output. A buffer amplifier is basically a high gain DC amplifier. It is basically used for transferring voltage from a high output impedance level to a low input impedance level circuit.

7. The direction of rotation of a CD is clockwise.

a) True

b) False

Answer: b

Explanation: CD stands for compact disk. The direction of rotation of Compact Disk is anticlockwise.

8. What is the full form of PAM?

a) Pulse Analog Modulation

b) Phase Analog Modulation

c) Pulse Amplitude Modulation

d) Phase Amplitude Modulation

Answer: c

Explanation: In communication, PAM stands for Pulse Amplitude Modulation. In PAM, the amplitude of the individual pulses of the message signal are varied in a specific time interval.

9. In a TV receiver antenna the length of reflector rod is _________

a) same as that of dipole

b) less than that of dipole

c) more than that of dipole

d) is half of that of dipole

Answer: c

Explanation: A dipole antenna is the one having its conductive wire rod equal to half the maximum wavelength of an antenna. The length of receiving antenna in a TV receiver must be more than that of dipole to get a better reception of signals.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Advantages of Filter Method”.

1. Which of the following does not cause losses in optical fibre cables?

a) Stepped index operation

b) Scattering

c) Microbending

d) Light absorption

Answer: a

Explanation: In Stepped index operation, refractive index within the core is uniform. There is also a sharp decrease in refractive index at the core-cladding interface. It generally does not cause any type os losses in optical fibre cables.

2. In televisions, equalizing pulses are sent during __________

a) horizontal blanking

b) vertical blanking

c) serrations

d) horizontal retrace

Answer: a

Explanation: The duration of an equalizing pulse is approximately 2.5 microseconds. The repetition frequency of equalizing pulses is twice the line frequency. It is necessary to sent equalizing pulses during horizontal blanking in televisions.

3. It is generally observed that a ship to ship communication suffers from fading. This problem can be avoided by using ________

a) space diversity

b) frequency diversity

c) directional antenna

d) filter

Answer: b

Explanation: It is generally observed that a ship to ship communication suffers from fading. This problem can be avoided by using frequency diversity in which the components of a radio wave are received from different channels thus reducing the error that occurs in the transmission of a single frequency component.

4. What is the characteristic impedance of a twin wire feeder used in television?

a) 1000 ohm

b) 100 ohm

c) 10 ohm

d) 300 ohm

Answer: d

Explanation: Twin wire feeder consists of two wires with spacers. For a twin wire feeder the characteristic impedance should be close to 300 ohm.

5. A buffer amplifier is a cathode follower double tuned amplifier.

a) True

b) False

Answer: b

Explanation: Gain of an amplifier is it’s ability to increase the voltage at the input and produce the result at the output. A buffer amplifier is basically a high gain DC amplifier. It is basically used for transferring voltage from a high output impedance level to a low input impedance level circuit.

6. What is the direction of rotation of a CD?

a) anticlockwise

b) clockwise

c) either clockwise or anticlockwise depend on data stored

d) first anticlockwise and then clockwise

Answer: a

Explanation: CD stands for compact disk. The direction of rotation of Compact Disk is anticlockwise.

7. According to Fourier Analysis a square wave can be represented as a fundamental sine wave and even harmonics.

a) True

b) False

Answer: b

Explanation: A square wave is a periodic non-sinusoidal waveform with an uniform frequency, in which the amplitude alternates between a fixed maximum and minimum value. According to Fourier analysis, a square wave can be represented as an infinite sum of sinusoidal waves. A square wave consists of only components of odd integer harmonics.

8. Filter method is the one and only method to produce SSB.

a) True

b) False

Answer: b

Explanation: SSB can be produced by filter method also known as frequency discrimination method. It can also be produced by phase discrimination method.

9. Impulse noise can be reduced in _________

a) FM

b) AM

c) QAM

d) PM

Answer: a

Explanation: Impulse noise includes unwanted, almost instantaneous sharp sounds. It is only in frequency modulated circuits that allow reduction in impulse noise.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Disadvantages of Filter Method”.

1. Why sampling is used in communication?

a) for getting higher speed of communication

b) for getting higher efficiency

c) cheaper equipment is required

d) for a better transmission

Answer: a

Explanation: Sampling is the conversion of continuous-time signal to discrete-time signal. It samples a continuous time signal depending on a specific range and thus produces the discrete form of the signal. It is highly used in communication for getting higher speed of communication.

2. Which two noises are present in Delta Modulation ?

a) Slope overload and Thermal noise

b) Granular and shot noise

c) Slope overload and granular noise

d) Thermal and shot noise

Answer: c

Explanation: Delta modulation is used for transmission of voice information where quality is not the primarily importance. Its drawback is it has two noises namely slope overload and granular noise. Slope overload noise occurs when the input signal slope is higher than the delta modulator’s capability. Granular noise is produced due to level input signal resulting into the oscillatory output. So for getting rid of these noises we use ADM .

3. Varacter is used for generation of ________

a) PM signals only

b) FM signals only

c) AM signals only

d) DSB-SC signals

Answer: b

Explanation: Varacter diode or tuning diode that has a variable capacitance. It is operated as reverse-biased and therefore no current flows. It is mainly used for generation of FM signals only.

4. What will happen in amplitude modulation, if the modulation index is more than 1?

a) bandwidth will increase

b) bandwidth will decrease

c) amplitude becomes constant

d) waves will get distorted

Answer: d

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. If modulation index is greater than 1, then the wave gets distorted and overlap, thus causing overmodulation.

5. The adverse effect of noise in communication system can be seen in ________

a) receiver

b) transmitter

c) source

d) channel

Answer: d

Explanation: Noise is the unwanted signal present in the passband of a signal. It is very much unpleasant thus causing disturbance. Its adverse effect is highly seen on channel.

6. Which among the following is not an advantage of FM over AM?

a) modulating power required is less

b) low bandwidth is required

c) better noise immunity

d) better signal to noise ratio

Answer: b

Explanation: Advantages of FM over AM are less prone to noise, low modulating power required and such like. However, disadvantage of FM is that large bandwidth is required.

7. Which of the following is the advantage of base modulation over collector modulation of a class C amplifier?

a) lower modulation power is required

b) higher power output per transistor

c) better efficiency

d) better linearity of modulation

Answer: a

Explanation: Base modulation is preferred over collector modulation of a class C transistor because low modulating power is required and collector saturation prevents complete modulation of a signal. Generally, Collector modulation has more advantages over Base modulation like high linearity, better collector efficiency and such like.

8. What is the radio frequency range of a frequency modulated signal?

a) 20-80 MHz

b) 100-200 MHz

c) 200-350 MHz

d) 99-108 MHz

Answer: d

Explanation: The standard frequency range of a frequency modulated signal is between 90-105 MHz.

9. Vestigial side band  is most commonly used in ________

a) Television Transmission

b) Radios

c) Telephony

d) Laser Transmission

Answer: a

Explanation: Vestigial Sideband Modulation  is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. Thus, television production is done using VSB modulation.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Phase Shift Method”.

1. Which of the following is an indirect way of generating frequency modulated signals?

a) Armstrong modulator

b) Varacter diode modulator

c) Reactance FET modulator

d) Reactance modulator

Answer: a

Explanation: Varacter diode modulator is not an indirect way of generating FM. Instead it’s a direct way of producing FM with the help of voltage controlled oscillator mechanism. It is Armstrong modulator which is an indirect way of generating FM.

2. Which of the following determines carrier deviation in frequency modulation?

a) modulating voltage

b) modulating frequency

c) frequency deviation

d) modulating phase

Answer: a

Explanation: In frequency modulation, frequency of carrier varies with the modulating voltage. In frequency modulation, it is modulating voltage that is responsible for deviation of the carrier.

3. Balance modulator is used to produce __________

a) DSB

b) VSB

c) AM

d) SSB

Answer: a

Explanation: A balance modulator mixes audio signal and radio frequency carrier wave, thereby producing a DSBSC wave, by suppressing the carrier. In DSB_SC, only the two sidebands are present. Thus, it has less power consumption.

4. Full AM signal is preferred over SSB in broadcasting purpose because ________

a) generation of full AM is easier

b) detection of full AM is simpler

c) requires large bandwidth

d) for both detection and generation of full AM

Answer: b

Explanation: SSB is preferred because of its low bandwidth and lesser power consumption. It reduces its bandwidth by suppressing the carrier and removing one of the two sidebands since both sidebands are exactly same. But full amplitude modulation is sometimes preferred over it because in its detection of full AM is simpler due to it’s simpler demodulation circuit.

5. Which among the following is not necessarily the advantage of SSB over AM?

a) required bandwidth for SSB is low

b) less power handled

c) complex circuit

d) simple circuit

Answer: d

Explanation: SSB is preferred because of its low bandwidth and lesser power consumption. It reduces its bandwidth by suppressing the carrier and removing one of the two sidebands since both sidebands are exactly same. But full amplitude modulation is sometimes preferred over it because in it detection of full AM is simpler due to it’s simpler demodulation circuit. SSBSC has a complex circuit anyway.

6. Which filter is used to get back the original signal from sampled signal?

a) low pass filter

b) high pass filter

c) band pass filter

d) band reject filter

Answer: a

Explanation: Sampling is the conversion of continuous-time signal to discrete-time signal by sampling the continuous signal with respect to specific time intervals, thereby discritising it. Now to get back the original signal we have to use low pass filter, which attenuates high frequencies and allows only low frequencies to pass.

7. Carson’s rule is used to ________

a) calculate Bandwidth of FM signal

b) calculate SNR of FM signal

c) determine the carrier frequency

d) calculate Figure of merit of FM signal

Answer: a

Explanation: According to Carson’s rule, the required bandwidth is twice the sum of the maximum frequency deviation and the maximum modulating signal frequency or B = 2(f d + f m )Hz.

8. FM signals can be generated by using ________

a) Varacter diode

b) Laser diode

c) Backward diode

d) Gunn diode

Answer: a

Explanation: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly used in generation of FM signals using Voltage Controlled Oscillator.

9. Granular noise occurs in Delta Modulation, when ____________

a) pulse rate decreases

b) pulse amplitude decreases

c) modulating signal increases

d) modulating signal remains constant

Answer: d

Explanation: Delta modulation is used for transmission of voice information where quality is not the primarily importance. Its drawback is it has two noises namely slope overload and granular noise. Granular noise is produced due to constant modulating input signal resulting into oscillatory output. So for getting rid from these noises we use ADM .

10. DM stands for ________

a) Density Modulation

b) Delta Modulation

c) Double Side Band Modulation

d) Direct Modulation

Answer: b

Explanation: DM stands for Delta Modulation. Delta modulation is used for transmission of voice information where quality is not the primarily importance.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Generation of VSB”.

1. Which of the following oscillator is not found in FM?

a) Hartley Oscillator

b) Crystal Oscillator

c) Armstrong Oscillator

d) Dynatron Oscillator

Answer: b

Explanation: In frequency modulation, frequency of the carrier wave is varied with the instantaneous amplitude of message signal. Crystal oscillator is used to generate a carrier signal with a precise or fixed frequency. But it has no use in frequency modulation.

2. What is the approximated range of audio frequencies?

a) 20Hz to 20KHz

b) 20Hz to 200KHz

c) 10Hz to 10KHz

d) 20Hz to 20MHz

Answer: a

Explanation: The standard fixed range of audio frequencies is from 20HZ to 20 KHz.

3. What is duty cycle?

a) ratio of time on to time off

b) ratio of time off to time on

c) 1 ⁄ 2 × 

d) 1 ⁄ 2 × 

Answer: a

Explanation: Duty cycle is the fraction of time in which the system is active. It can also be defined as the ratio of time on to time off of a system. At times, duty cycle, expressed as percentage, is the ratio of time on to sum of time on and time off.

4. Which of the following is used for demodulation of PAM signal?

a) a band reject filter

b) a band pass filter

c) a low pass filter

d) a high pass filter

Answer: c

Explanation: Pulse Amplitude Modulation is the transmission of data by varying the amplitude of different pulses. A low pass filter is always used to demodulate a PAM as it attenuates high frequencies and allows only low frequencies to pass.

5. Which of the following is not a part of analogue communication?

a) PPM

b) AM

c) PCM

d) PWM

Answer: c

Explanation: Pulse code modulation  is a digital form of communication. It has no relation with analog communication. Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses.

6. For demodulation of PCM, it is first converted into ________

a) PAM

b) PWM

c) PPM

d) FM

Answer: a

Explanation: Pulse Code Modulation deals with converting an analog signal to a digital signal. During it’s demodulation, the wave to be treated is to be parallel. The series pulse wave signal is then converted into a parallel digital signal using a serial to parallel converter, after which it is further converted into the original analog signal with the help of a decoder or detector.

7. Inherently most noise resistant modulating system is _________

a) PCM

b) DSB

c) SSB

d) VSB

Answer: a

Explanation: In PCM, the amplitude of the analog signal is discritised and converted into digital form for transmission of binary data. PCM is least prone to noise and can travel long distances.

8. Which of the following modulation is used for radio navigation?

a) Pulse Modulation

b) Amplitude Modulation

c) Phase Modulation

d) Frequency Modulation

Answer: a

Explanation: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. It is mostly used for radio navigation and for many others.

9. Frequency modulated broadcast band generally lies in ________

a) VHF

b) HF

c) SHF

d) LF

Answer: a

Explanation: VHF  is the ITU designation for the range of radio frequency from 30MHz to 300MHz. Frequency modulated broadcast band generally lies in it only. HF ranges from 3MHz to 30MHz while SHF ranges from 3GHz to 30GHz. And LF ranges from 30KHz to 300KHz.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Applications of VSB”.

1. Frequency Modulated system needs less bandwidth.

a) True

b) False

Answer: b

Explanation: In frequency modulation, frequency of the carrier wave is varied with the instantaneous amplitude of the message signal. Thus, it requires large bandwidth.

2. When bandwidth is the major consideration a narrow and wide band FM can be approximated to?

a) DSB-SC

b) SSB

c) VSB

d) AM

Answer: d

Explanation: For narrow and wide bands frequency modulation, modulation index is respectively smaller and greater than 1. When bandwidth is considered it can be approximated to AM.

3. Which modulation is used in microwave band?

a) Amplitude Modulation

b) Pulse Modulation

c) Frequency Modulation

d) Phase Modulation

Answer: b

Explanation: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. It is mostly used for radio navigation, microwave band and for many others.

4. All the output pulses are at full transmitter power for a strong signal in all of the following except ________

a) PAM

b) PFM

c) PCM

d) PWM

Answer: a

Explanation: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. Pulse amplitude modulation varies amplitude of pulses for transmission of data. Its’ output pulses are not at full transmitter power for a strong signal and thus it is an exception.

5. In pulse transmitter, the ratio of time on to time off is called ________

a) base

b) bandwidth

c) duty cycle

d) efficiency

Answer: c

Explanation: Duty cycle is the fraction of time in which the system is active. It can also be defined as the ratio of time on to time off of a system. At times, duty cycle, expressed as a percentage, is the ratio of time on to sum of time on and time off.

6. In which of the following modulated systems, quantization noise occurs?

a) TDM

b) FM

c) PWD

d) PCM

Answer: d

Explanation: The difference between an input value and its quantized value is called quantization error or we can also see it as that when an analog number is not converted into an exact digital number. It takes place in pulse code modulation . Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses.

7. Signal to quantization noise ratio in PCM system depends on _________

a) sampling rate

b) signal bandwidth

c) number of quantization levels

d) nature of carrier wave

Answer: c

Explanation: Pulse code modulation  is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only. Signal to quantization noise ratio depends on the number of quantization levels.

8. Pulse Modulation can be used in automatic landing equipments.

a) True

b) False

Answer: a

Explanation: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. It is mostly used for radio navigation, microwave band and for many others.

9. Which of the following modulation is used in data communication?

a) Pulse Modulation

b) Amplitude Modulation

c) Phase Modulation

d) Frequency Modulation

Answer: a

Explanation: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. It is mostly used for radio navigation, microwave band and for many others. It is also highly used in data communication.

This set of Analog Communications Interview Questions and Answers for Experienced people focuses on “Comparision of SSB Suppression Techniques”.

1. What is the expected modulation index in case of wide band FM?

a) less than 1

b) 1

c) 1 ⁄ 2

d) more than 1

Answer: d

Explanation: For producing Narrow band frequency modulated wave, modulation index should be less than or equal to1. For wideband frequency modulated wave, modulation index should be greater than 1.

2. What is the expected modulation index in case of narrow band FM?

a) less than or equal to 1

b) infinite

c) 1.5

d) more than 1

Answer: a

Explanation: For producing Narrow band frequency modulated wave, modulation index should be less than or equal to1. For wideband frequency modulated wave, modulation index should be greater than 1.

3. Which of the following statement is true about pulse position modulation system?

a) pulses have constant width but varying amplitude

b) pulses have constant amplitudes and constant widths

c) pulses have constant amplitude but varying widths

d) pulses have varying width and varying amplitude

Answer: b

Explanation: Pulse Position Modulation  is a type of modulation process in which position of the pulse of the carrier wave is varied with respect to the instantaneous position values of the message signal. In pulse modulation, pulses have constant amplitude and widths.

4. IF stage is a receiver employs ________

a) impedance coupling

b) capacitive coupling

c) single tuned transformer coupling

d) double tuned transformer coupling

Answer: d

Explanation: A frequency to which a carrier wave is shifted as an intermediate step is known as Intermediate Frequency. It employs double tuned transformer coupling.

5. In higher power AM transmission, modulation is done at _________

a) Source stage

b) Transducer Stage

c) Oscillator stage

d) RF power stage

Answer: d

Explanation: RF power amplifier converts a low power radio frequency signal to high power. Modulation is done at RF power stage for high power AM transmission.

6. If modulation index of an AM was in changed from 0 to 1, then transmitted power ________

a) increases by 100%

b) increases by 50%

c) increases by 75%

d) increases by 25%

Answer: b

Explanation: Modulation index indicates amount of modulation in the carrier signal. If modulation index changes to 1 from 0, its transmitted power increases by 50%.

7. In PCM system, output S/N increases ________

a) parabolically with bandwidth

b) exponentially with bandwidth

c) inversely with bandwidth

d) linearly with bandwidth

Answer: b

Explanation: Pulse code modulation  is a digital form of communication. Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses. if we calculate the ratio of signal to noise ratio for different bandwidth then we observe that it increases exponentially with it.

8. Companding is used in PCM transmitters to overcome quantizing noise in PCM.

a) True

b) False

Answer: b

Explanation: Companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Modulation of VSB Modulated Wave”.

1. Quantization noise occurs in ________

a) Frequency Division Multiplexing

b) Time Division Multiplexing

c) Delta Modulation

d) Amplitude Modulation

Answer: d

Explanation: Quantisation is the process through which a range of continuous analog values are quantized or rounded off to a single value, thereby forming samples of a discrete digital signal. Quantisation Error occurs when there is a difference between an input value and it’s quantized value. Quantisation occurs when an analog signal is converted into it’s digital form, thus it occurs in Pulse Code modulation .

2. Which is the greatest disadvantage of Pulse Code Modulation?

a) highly prone to noise

b) cannot travel long distances

c) its inability to handle analog signals

d) large bandwidth is required for it

Answer: d

Explanation: Pulse code modulation  is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only. Its greatest disadvantage is its requirement for large bandwidth.

3. Inductance and capacitance of a line is 0.8 μH ⁄ m and 32 pF ⁄ m . Find Z 0 ?

a) 158

b) 166

c) 143

d) 127

Answer: a

Explanation:

analog-communications-questions-answers-modulation-vsb-modulated-wave-q3

4. Pulse communication system that is inherently highly immune to noise is ________

a) PCM

b) PPM

c) PAM

d) PWM

Answer: a

Explanation: Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses. It is less prone to noise and can travel through long distances without loss of data.

5. What the main advantage of PCM?

a) can travel small distances

b) higher bandwidth

c) lower noise

d) good reception

Answer: c

Explanation: Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses. It is less prone to noise and can travel through long distances without loss of data.

6. In AM pilot carrier, transmission has ________

a) carrier and part of one side band

b) two side bands and a carrier

c) two side bands

d) carrier, one side band and part of other side band

Answer: b

Explanation: In amplitude modulated wave, the transmitted wave has two side bands and a carrier. Thus it’s bandwidth is twice the maximum modulating frequency.

7. Quantization noise depends upon both sampling rate and number of quantization levels.

a) True

b) False

Answer: b

Explanation: Quantization noise in pulse code modulation  depends upon only on number of quantization levels.

8. Which of the following frequency is not transmitted in AM transmission?

a) Upper side band frequency

b) Carrier frequency

c) Lower side band frequency

d) Audio frequency

Answer: d

Explanation: Audio frequency is the frequency that is not transmitted in AM transmission.

9. Companding is used in PCM transmitters to allow amplitude limiting in the receivers.

a) True

b) False

Answer: b

Explanation: Companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio.

10. What is the use of Companding?

a) in PCM transmitters to allow amplitude limiting in the receivers

b) in PCM receiver to overcome impulse noise

c) to overcome quantizing noise in PCM

d) to protect small signals in PCM from quantizing distortion

Answer: d

Explanation: Companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio. It is mainly used to protect small signals in PCM from quantizing distortion.

This set of Analog Communications online test focuses on “Demodulation of VSB Modulated Wave”.

1. What is the reason of “envelope” in an amplitude modulated signal?

a) noise signal

b) carrier signal

c) nematic signal

d) baseband signal

Answer: d

Explanation: Envelope is basically a smooth curve that outlines the extremes of any baseband signal. So basically it is message or baseband signal that determines the envelope.

2. AM stands for ________

a) Amplitude Modulation

b) Audio Modulation

c) Antenna Modulation

d) Amplified Modulation

Answer: a

Explanation: AM stands for amplitude modulation. Amplitude modulation is the change in the amplitude of carrier wave in proportion to the instantaneous amplitude of the message signal.

3. What is the equation for full-carrier AM?

a) V = (E c + E m ) × (sin⁡ ω c t)

b) V = (E c + E m ) × (sin⁡ ω m t) + (sin⁡ ω c t)

c) V = (E c × E m ) × (sin ⁡ω m t) × (sin⁡ ω c t)

d) V = (E c + E m sin⁡ ω m t) × (sin ⁡ω c t)

Answer: d

Explanation: Amplitude modulation is the change in the amplitude of carrier wave in proportion to the instantaneous amplitude of the message signal. A carrier can be seen as a waveform with frequency higher than the message signal frequency, that is modulated with respect to input signal for the purpose of transmitting information. The equation for full-carrier AM is V = (E c + E m sin⁡ω m t) × (sin ⁡ω c t).

4. What is the cause of Overmodulation?

a) distortion

b) splatter

c) both distortion and splatter

d) half reception of signals

Answer: c

Explanation: Overmodulation is the process in which the modulation index is greater than 1 such that the modulating signal voltage exceeds the required voltage to produce 100% modulation. It results out of both distortion and splatter of waveform and causes distortion and overlapping.

5. If AM radio station increases its modulation index then the audio gets louder at the receiver.

a) True

b) False

Answer: a

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. If we increase the modulation index then audio signal gets louder.

6. The modulation index can be derived from ________

a) frequency-domain signal

b) time-domain signal

c) both frequency and time domain signal

d) a highly modulated carrier wave

Answer: c

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. It can be derived for frequency-domain signals as well as for time-domain signals.

7. A single sideband modulation system is more efficient than a plain amplitude modulated system.

a) True

b) False

Answer: a

Explanation: In Single Sideband transmission, the carrier is suppressed and only either of the two sidebands is transmitted. Thus, it reduces the total power consumption and also reduces the bandwidth required. Whereas, in AM, the carrier being transmitted along with both the sidebands entails more power and larger bandwidth.

8. At peak modulation an SSB transmitter radiate 1000W, what will it radiate with no modulation?

a) 1000 watts

b) 500 watts

c) 250 watts

d) 0 watts

Answer: d

Explanation: Power of a modulated wave is directly proportional to modulation index. Thus, if there is no modulation in any SSB transmitter than, it will not radiate. So it will radiate 0 watts when there is no modulation.

9. Why AM stations has “low-fidelity”?

a) AM is susceptible to noise

b) Commercial AM stations use low power

c) Commercial AM stations have a narrow bandwidth

d) High quantization to noise ratio

Answer: c

Explanation: Fidelity is the ability of receivers to reproduce all modulating signals eually. Low fidelity can be seen as sound recording that contain technical flaws to make sound better compared with the sound that is recorded live. High fidelity refers to the equipment that very accurately produces without any harmonic or resonance. AM stations have low fidelity to have narrow bandwidth.

This set of Analog Communications Questions and Answers for Aptitude test focuses on “Spectrum of AM SC Waves”.

1. What is the modulation index of an AM signal if the peak voltage goes from E max to E min ?

a) \

 

 \

 

 \

 

 \(\frac{E_{max} + E_{min}}{E_{max} – E_{min}}\)

Answer: c

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. It is defined as \(\frac{E_{max} – E_{min}}{E_{max} + E_{min}}\) where E max and E min are respectively the maximum and minimum voltage of the modulated wave.

2. Which frequencies is produced if V a sin⁡(ω a t) amplitude modulates the carrier V c sin⁡(ω c t)?

a) (ω c + ω a ), (ω c – ω a ) and ω c

b) (ω c ) and (ω a )

c) (ω c + ω a ) and (2ω c + 2ω a )

d) (2ω c ) and (2ω a )

Answer: a

Explanation: If we modulate the carrier signal having frequency ω c with respect to the message wave having frequency ω a , then the resultant modulated wave has frequency components (ω c + ω a ), (ω c – ω a ) and ω c .

3. What is the total sideband power if there is 100% modulation?

a) half the carrier wave

b) twice the carrier wave

c) equal to the carrier wave

d) one-fourth of the carrier wave

Answer: a

Explanation: The sidebands are identical to each other and contain same information. Thus, for 100% modulation, value of modulation index should be equal to 1. If modulation index, m=1 then total sideband power is equal to the half of carrier wave.

4. If AM radio station increases its modulation index then there is an increase in receiving RF signal.

a) True

b) False

Answer: a

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. Increase in it also increase the ability of increase reception of RF signals.

5. How an AM radio station increase its signal-to-noise ratio?

a) by increasing its modulation index

b) by decreasing its modulation index

c) by maintaining a constant modulation index

d) by increasing the frequency

Answer: a

Explanation: Signal to noise ratio is the ratio of signal power to the noise power. It is the measure of signal present with respect to the surrounding noise. It is directly proportional to the modulation index and thus it increases with modulation index.

6. What is the main problem in using quadrature amplitude modulation?

a) high bandwidth is required

b) high power is required

c) incompability with ordinary AM radio waves

d) bandwidth required is less

Answer: c

Explanation: Quadrature Amplitude Modulation  is widely used for combining two amplitude modulated waves into a single channel. It is both an analog and digital modulation technique. It has many advantages over other modulations such as PSK but its disadvantage is its incompability with ordinary radio waves.

7. A single sideband modulation system requires a more complex demodulator circuit.

a) True

b) False

Answer: a

Explanation: In Single Sideband transmission, the carrier is suppressed and only either of the two sidebands is transmitted. Thus, it reduces the total power consumption and also reduces the bandwidth required. For its demodulation it requires a complex demodulator circuit

8. To demodulate a USB SSB signal, the receiver must ________

a) be set to USB mode

b) reinsert the carrier

c) be set to USB mode and reinsert the carrier

d) have low-fidelity

Answer: c

Explanation: Single side band suppresses the carrier and uses only one of the two sidebands. The two sidebands carry exactly the same information and thus removing a sideband does not have any effect on the signal. To demodulate upper sideband of signal it is necessary that the receiver must be set to USB mode and have the ability to reinsert the carrier.

9. The __________ of an AM signal resembles the shape of baseband signal.

a) upperband

b) lowerband

c) efficiency

d) envelope

Answer: d

Explanation: Envelope is basically a smooth curve that outlines the extremes of any baseband signal in the amplitude modulated wave. So basically it is message or baseband signal that determines the envelope.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Chopper Circuit”.

1. What is the full form of PEP in communication?

a) Peak Efficiency Power

b) Peak Envelope Power

c) Peak Efficiency Product

d) Peak Envelope Power

Answer: d

Explanation: PEP in communication stands for Peak Envelope Power. It is the highest envelope power that is transmitted to antenna transmission line by a transmitter. It is used to measure the power of varying signals.

2. Only audio can be sent using Amplitude Modulation.

a) True

b) False

Answer: b

Explanation: Amplitude modulation has the capability to send audio, video and digital data using different amplitude modulation techniques. So the statement that only audio signal can be sent by amplitude modulation is wrong.

3. What is the total modulation index, if one wave has a modulation index of m 1 and other wave has a modulation index of m 2 ?

a) m 1 + m 2

b) \

 

 \ \(\sqrt{ + }\)

Answer: d

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. The total modulation index of two waves having modulation index m 1 and m 2 is \(\sqrt{ + }\).

4. How many sidebands is produced with a single tone in an amplitude modulated system?

a) One

b) Two

c) Three

d) Four

Answer: b

Explanation: Single tone modulation is that in which the modulation is carried out with a message signal having single frequency component. Thus, the modulated wave has two sidebands.

5. If we compared to the USB, the information in LSB is ________

a) different to USB

b) twice of USB

c) same as USB

d) half of USB

Answer: c

Explanation: The two bands i.e. upper sideband and lower sideband generally contains same information. They also has same power.

6. In amplitude modulated system, total sideband power is ________ than the carrier power.

a) always less

b) always more

c) sometimes more

d) sometimes less

Answer: b

Explanation: If we take the total power, then it is the sum of the carrier power and power of all the sidebands produced in the modulated signal. Thus, the total power is always more than the carrier power.

7. An amplitude modulated system requires less bandwidth than single side band system.

a) True

b) False

Answer: b

Explanation: In Single Sideband transmission, the carrier is suppressed and only either of the two sidebands is transmitted. Thus, it reduces the total power consumption and also reduces the bandwidth required. The two sidebands carries exactly the same information and thus removing a sideband does not have any effect on the signal.

8. In SC in DSB-SC stands for _________

a) suppressed-carrier

b) single-carrier

c) sideband-carrier

d) super-carrier

Answer: a

Explanation: DSB-SC stands for Double Side Band- Suppressed Carrier. In SBSC, the carrier is suppressed and only the two sidebands are transmitted. In DSB-SC all the frequencies produced by amplitude modulation are symmetrically arranged above and below the carrier frequency.

9. What is the correct statement about FM modulation index?

a) increases with both modulation frequency and deviation

b) decreases with modulation frequency and increases with deviation

c) it increase with modulation frequency and decreases with deviation

d) it is equal to twice the deviation

Answer: b

Explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. In FM, modulation index is the ratio of frequency deviation and modulating frequency. Frequency modulated modulation index increases as deviation increase. It also decreases with modulation frequency.

10. Which mathematically term is used for calculating FM bandwidth?

a) Bessel functions

b) Trigonometry

c) Taylor series

d) Fractals

Answer: a

Explanation: Bessel function are the solution of Bessel differential equation which are non-singular at the origin. In communication it is used to calculate FM bandwidth.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Switching Circuit”.

1. If we compared to the USB, the power in the LSB is ________

a) one-fourth of USB

b) twice of USB

c) same as USB

d) half of USB

Answer: c

Explanation: Generally, USB  and LSB  contain same information and are identical to one another. Thus, both entail same power.

2. What will be the effect on power in amplitude modulated system if we increase the modulation index?

a) increases

b) becomes twice

c) remains same

d) decreases

Answer: a

Explanation: If we increase or decrease the modulation index, accordingly the power of amplitude modulated system will also increase or decrease. This is because the power is directly proportional to the modulation index.

3. What is the modulation index for getting maximum power in amplitude modulated system?

a) 1

b) 1 ⁄ 2

c) 0.3

d) 0.8

Answer: a

Explanation: For getting maximum power, it is required to set the maximum and minimum voltage of the modulated wave such that we get modulation index equal to unity. This implies 100% modulation.

4. How can we derive FM from PM?

a) by integrating the modulating signal before applying to the PM oscillator

b) by integrating signal out of the PM oscillator

c) by differentiating the modulating signal before applying to the PM oscillator

d) by differentiating signal out of the PM oscillator

Answer: a

Explanation: Frequency modulation can be derived from phase modulated system, if we integrate our modulating signal before applying our wave to PM oscillator. Likewise, Phase modulation can be obtained from frequency modulated system, if we differentiate our modulating signal before applying our wave to FM oscillator.

5. FM bandwidth can be approximated by ________

a) Carson’s rule

b) Armstrong’s rule

c) Bessel’s rule

d) Pythagoras rule

Answer: a

Explanation: According to Carson’s rule, the required bandwidth is twice the sum of the maximum frequency deviation and the maximum modulating signal frequency.

B = 2(f d +f m )Hz.

6. Which effect is observed when FM reception deteriorates abruptly due to noise?

a) Threshold effect

b) Capture effect

c) Noise effect

d) Limit effect

Answer: a

Explanation: Signal to Noise ratio is the measure of signal present with respect to the surrounding noise. Threshold effect has low output signal to noise ratio. It contains large noise as compared to input signal in envelope detector. In threshold effect, detection of message signal is difficult.

7. FM stereo _________

a) is implemented using an SCA signal

b) has a higher signal to noise ratio than mono FM

c) is not compatible with mono FM

d) uses DSBSC AM modulation

Answer: d

Explanation: A stereo FM contains three major sections :- monomode, stereo mode and section common to both mono and stereo mode. The stereo section is much complicated than others. It uses DSBSC AM modulation, in which the carrier is suppressed and only the two sidebands are transmitted, for its process.

8. Signal to noise ratio of a frequency modulated system is better than amplitude modulated system.

a) True

b) False

Answer: a

Explanation: Signal to noise ratio is the ratio of signal power to the noise power. It is often described in decibels. Signal to noise ratio is the ratio of signal power to the noise power. It is the measure of signal present with respect to the surrounding noise. It is directly proportional to the modulation index and thus it increases with modulation index. It is better for frequency modulated systems.

9. What will be the effect on power if the distance between the sidebands and center frequency increases?

a) power decreases

b) power increases

c) power remains same

d) power becomes twice of its previous value

Answer: a

Explanation: If the distance between the central frequency and sidebands increases, the effective power decreases as bandwidth increases.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Non Linear Device”.

1. Who originated the theory of radio waves?

a) Marconi

b) Bell

c) Hertz

d) Maxwell

Answer: d

Explanation: Maxwell was the first person who came up with the concept of electromagnetic theory and from there, the theory of radio waves was deduced. After some years, it was Hertz who applied Maxwell theories to the production and reception of waves.

2. Which effect is characteristic of FM reception in a noisy environment?

a) threshold effect

b) capture effect

c) bessel effect

d) carson’s effect

Answer: a

Explanation: Signal to Noise ratio is the measure of signal present with respect to the surrounding noise. Threshold effect has low output signal to noise ratio. It contains large noise as compared to input signal in envelope detector. In threshold effect, detection of message signal is difficult.

3. Mathematically, the number of sidebands in frequency modulated system is _________

a) infinite

b) one

c) two

d) zero

Answer: a

Explanation: Wideband frequency modulated system has modulation index greater than 1. Thus, if we consider the number of sidebands in wideband frequency modulated system, we find it to be infinite, mathematically speaking.

4. Which statement is true about an SCA signal?

a) it can use amplitude modulation

b) it can use frequency modulation

c) is monaural

d) it can use amplitude as well as frequency modulation and is also monaural

Answer: d

Explanation: STC stands for Subsidiary Communication Authority. SCA is a separated data channel which is transmitted along with the main signal over a broadcast station. It can either be amplitude modulated or frequency modulated. It being monaural means that multiples audio signals are mixed and then passed through a single channel.

5. What is the use of pre-emphasis?

a) to increase the signal to noise ratio for higher audio frequencies

b) to allow stereo audio to be carried by FM stations

c) to increase the signal to noise ratio for all audio frequencies

d) to increase the signal to noise ratio for lower audio frequencies

Answer: d

Explanation: Pre-emphasis is applied in communication systems to improve signal strength before transmission. It refers to boosting the amplitudes of the weak modulating voltages for high audio frequencies. It is also helpful in increasing S/N ratio but for lower audio frequencies only.

6. In FM system, capture effect is observed when an FM receiver switching suddenly between two stations having nearby frequencies.

a) True

b) False

Answer: a

Explanation: Capture effect is related with FM reception. In capture effect, only the stronger of two signals at, or near, the same frequency will be demodulated.

7. What is the full form of NBFM?

a) Narrow band frequency modulation

b) National broadcast frequency modulation

c) Near band frequency modulation

d) Non broadcast frequency modulation

Answer: a

Explanation: NBFM stands for Narrow band frequency modulation. For NBFM, modulation index should be less than equal to 1.

8. Why the bandwidth of an FM signal is considered to be limited?

a) because there can only be a finite number of sidebands

b) because it is equal to the frequency deviation

c) because it is band-limited at the receiver

d) because the power in the outer sidebands is negligible

Answer: d

Explanation: In frequency modulation system, frequency of the carrier wave is varied in proportion with the instantaneous amplitude of the message signal, which is to be transmitted. IN Wideband FM, the number of sidebands are infinite. Thus, using Carson’s rule, the bandwidth of FM signal is kept limited considering the power impact of other sidebands negligible.

This set of Analog Communications Assessment Questions and Answers focuses on “SSB with Large Carrier”.

1. The time taken by the charge carrier to cross from the emitter to the collector is called ________

a) miller time

b) transit time

c) charge time

d) relaxing time

Answer: b

Explanation: Transit time is that time which is taken by the charge carriers to move from emitter to collector.

2. The person who sent the first radio signal across the atlantic ocean was ________

a) Marconi

b) Maxwell

c) Hertz

d) Bell

Answer: a

Explanation: Marconi is the first person who sent the first radio signal across the atlantic ocean. It was Maxwell who originated the theory of radio waves. After some years, it was Hertz who applied Maxwell theories to the production and reception of waves.

3. What is the use of bypass capacitor?

a) to remove RF from non-RF circuits

b) to couple RF around an amplifier

c) acts as low pass filter

d) acts as high pass filter

Answer: a

Explanation: A bypass capacitor is generally used to dampen the AC or noise present at all frequencies. In communication, it is used to remove RF from non-RF circuits.

4. The ability to change the operating frequency rapidly without a lot of retuning is called ________

a) Agility

b) VCO

c) Mixing

d) Filtering

Answer: a

Explanation: Agility is the process of changing operating frequency rapidly without a lot of returning.

5. A resonant circuit is used in narrowband RF amplifiers.

a) True

b) False

Answer: a

Explanation: The quality factor Q, of a resonant circuit is a measure of a quality of resonant circuit, thus indicating the performance of the resonant circuit. Bandwidth can be seen as the ratio of the resonant frequency to quality factor. A higher value for Q means a more narrow bandwidth, which we want in many application.

6. What is the full form of ALC?

a) Amplitude Level Control

b) Automatic Level Control

c) Automatic Limiter Control

d) Amplitude Limiter Control

Answer: b

Explanation: ALC stands for Automatic Level Control. It is a technology that is used for automatic control of output power.

7. In high level amplitude modulation, power in the sidebands comes from _________

a) Modulating amplifier

b) RF amplifier

c) Driver stage

d) Carrier

Answer: a

Explanation: In amplitude modulated system, amplitude of the carrier wave is varied in proportion to the amplitude of the original message wave which is to be transmitted. For high level amplitude modulation, power amplifiers are not required and modulating amplifiers is used to give power to sidebands.

8. To generate a SSB signal ________

a) Full carrier AM is required

b) DSB-SC is required

c) Quadrature signal is required

d) High frequency signal is needed

Answer: b

Explanation: Single side band suppressed carrier modulation technique suppresses the carrier and transmits either of the two sidebands. Thus, this not only reduces the power consumed but also reduces the bandwidth. SSB-SC technique requires a DSB-SC to be passed through a bandpass filter.

9. Which statement is true about direct FM modulator?

a) it integrates the modulating signal

b) it differentiates the modulating signal

c) varies the frequency of carrier oscillator

d) varies the phase of carrier oscillator

Answer: c

Explanation: Frequency modulated system can be produced either by direct ways or indirect ways. Armstrong method comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator, thus being known as frequency discrimination method, while indirect FM modulator varies the phase of carrier oscillator, thus being called phase discrimination method.

10. Which statement is true about indirect FM modulator?

a) it integrates the modulating signal

b) it differentiates the modulating signal

c) varies the frequency of carrier oscillator

d) varies the phase of carrier oscillator

Answer: d

Explanation: Frequency modulated system can be produced either by direct ways or indirect ways. Armstrong method comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator, thus being known as frequency discrimination method, while indirect FM modulator varies the phase of carrier oscillator, thus being called phase discrimination method.

This set of Analog Communications Multiple Choice Questions & Answers focuses on “Instantaneous Frequency and Frequency Modulation”.

1. What we use for impedance matching in RF amplifiers?

a) RC coupling

b) Transformer coupling

c) Direct coupling

d) RF coupling

Answer: b

Explanation: Impedance matching is the input impedance of an electrical load or the output impedance of corresponding electrical signal source to maximize power transfer or minimize signal reflection from the load. Transformer coupling is basically used for impedance matching in RF amplifiers. It is usually used with a small load for power amplification.

2. Neutralization cancels unwanted feedback by bypassing the feedback to the neutral or ground plane.

a) True

b) False

Answer: b

Explanation: Neutralization cancels unwanted feedback by adding feedback out of phase with the unwanted feedback. It is a method of filtering noise out of signals.

3. In a receiver, distortion can occur in ________

a) Mixer

b) Detector

c) IF amplifiers

d) Either mixer or detector or IF amplifiers

Answer: d

Explanation: Distortion in a receiver can occur in either mixer or in the detector. It can also occur in IF amplifiers. Distortion is the change in the shape of the waveform.

4. How we limit the response of a receiver to a weak signal?

a) by the AGC

b) by the noise that is generated in the receiver

c) by the dynamic range of the receiver

d) by the type of detector circuit being used

Answer: b

Explanation: The response of a receiver to weak signals is limited by the noise. This noise is generated in the receiver only. Noise is the unwanted signal that is present in the passband of the signal.

5. When aliasing will take place?

a) Sampling signals less than Nyquist Rate

b) Sampling signals more than Nyquist Rate

c) Sampling signals equal to Nyquist Rate

d) Sampling signals at a rate which is twice of Nyquist Rate

Answer: a

Explanation: Aliasing causes different signals to become indistinguishable when sampled. It happens when the sampling rate is less than Nyquist rate. To prevent aliasing, sampling signals should be at a rate which is twice of Nyquist Rate.

6. A resonant circuit is a simple form of bandpass filter.

a) True

b) False

Answer: a

Explanation: The quality factor Q, of a resonant circuit is a measure of quality of resonant circuit, thus indicating the performance of the resonant circuit. Bandwidth can be seen as the ratio of the resonant frequency to quality factor. A higher value for Q means a more narrow bandwidth, which we want in many applications.

7. Which statement is true for high level amplitude modulation?

a) all RF amplifiers are of class A

b) all RF amplifiers can be nonlinear

c) minimum RF power is required

d) maximum RF power is required

Answer: b

Explanation: In high level AM, modulation is done at high power of carrier and modulating signal therefore output power is high. Therefore, power amplifiers are not used to boost the carrier and modulating signal. Thus, all RF amplifiers are non-linear.

8. Which statement is true for low level amplitude modulation?

a) all RF amplifiers are of class A

b) all RF amplifiers can be linear

c) minimum RF power is required

d) maximum RF power is required

Answer: b

Explanation: For low level AM, modulation is done at low power of carrier and modulating signal, so power amplifiers are used to boost the carrier and modulating signal. Therefore, output power is low. Thus, the amplifiers used are linear.

9. Which two networks can be used for impedance matching?

a) pi network and T network

b) pi network and bridge network

c) bridge network and T network

d) pi network and omega network

Answer: a

Explanation: If a source with low impedance is connected with a load with high impedance then the power that can pass through the connection is limited by higher impedance. Generally the two networks, pi and T are used for impedance matching.

10. Which statement is true about frequency multipliers?

a) they are essentially balanced modulators

b) they are essentially class C amplifiers

c) they are essentially class AB amplifiers

d) they are essentially mixers

Answer: b

Explanation: Frequency multiplier multiplies the frequency of the input by an integer, such that the output is a multiple of the input. Frequency multipliers are generally class C amplifiers.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Types of Frequency Modulation”.

1. Baseband compression produces ________

a) a small range of frequencies from low to high

b) a small range of different phases

c) a small range of angles

d) a small range of amplitude

Answer: d

Explanation: A signal compression method in a wireless network provides efficient transfer of compressed signal samples over serial data links in the system. Baseband compression produces a small range of amplitude.

2. Automatic Level Control  is used to keep the modulation index close to 100%.

a) True

b) False

Answer: a

Explanation: ALC stands for Automatic Level Control. It is a technology which is used for automatic control of output power. It helps in maintaining the output when there are varying changes in the input.

3. A signal that ________ must have linear power amplifier.

a) is complex

b) has variable frequency

c) is linear

d) has variable amplitude

Answer: d

Explanation: If any signal has variable amplitude then its amplifier must be linear. Others may or may not have the same but can possess non-linear amplifiers.

4. Transmitters are designed usually to derive a load impedance of ________

a) 50 ohms resistive

b) 150 ohms resistive

c) 250 ohms resistive

d) 500 ohms resistive

Answer: a

Explanation: Transmitter is an electronic device that produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. Transmitters are usually designed to derive a load impedance of 50 ohms resistive.

5. What we called a resistor if a transmitter is connected to a resistor instead of an antenna?

a) a test load

b) a temporary load

c) a dummy load

d) a heavy load

Answer: c

Explanation: If a transmitter is connected to resistor not antenna than it is called dummy load. Such a load is used for testing purposes to set the parameters of the transmitter, as it would have behaved in presence of an actual antenna.

6. A class D amplifiers is very efficient than other amplifiers.

a) True

b) False

Answer: a

Explanation: Class D amplifier is also known as a switching amplifier. It is operate as electronic switches, and not an electric gain device which is commonly used in most amplifiers. It also has high power conversion efficiency unlike other amplifiers.

7. The carrier is suppressed in ________

a) a mixer

b) a frequency multiplier

c) a transducer

d) a balance modulator

Answer: d

Explanation: A mixer is the one which mixes the audio frequency with the carrier frequency. A transducer converts a signal from one form to another. Balance modulator suppresses the carrier and leaves only the sidebands.

8. What is the full form of AFC?

a) Amplitude to frequency conversion

b) Automatic frequency conversion

c) Automatic frequency control

d) Audio frequency control

Answer: c

Explanation: AFC stands for Automatic frequency control. It is a method to automatically keep a resonant circuit tuned to a frequency of an incoming radio signal. It is used in receivers to tune to the desired frequency.

9. Mixing is used in communication to ________

a) raise the carrier frequency

b) lower the carrier frequency

c) to altered the deviation

d) to change the carrier frequency to any required value

Answer: d

Explanation: Mixing is used to change the frequency of carrier by mixing it with a radio frequency signal or audio signal. The frequency can be changed to any required value in communication.

10. On which factor the bandwidth required for a modulated carrier depends?

a) baseband frequency range

b) signal to noise ratio

c) carrier frequency

d) amplitude of carrier frequency

Answer: a

Explanation: Bandwidth can be seen as a range of frequencies within a band, that is used for transmitting a signal. A signal bandwidth depends on the baseband frequency range.

This set of Analog Communications test focuses on “Bandwidth of FM Signal with Arbitrary m”.

1. When two or more signals share a common channel, it is called ________

a) sub-channeling

b) channeling

c) switching

d) multiplexing

Answer: d

Explanation: Multiplexing is a method by which multiple analog or digital signals are combined to form a single complex signal. In multiplexing, many signals are combined into one signal and passed through a single channel, thus sharing the same medium.

2. One of the reason of distortion is shift in phase relationships between baseband frequencies.

a) True

b) False

Answer: a

Explanation: Phase distortion is the change in shape of the waveform. Thus, if we shift the phase relationships between baseband frequencies, it will ultimately result in distortion.

3. Miller effect can cause an amplifier to oscillate.

a) True

b) False

Answer: a

Explanation: Miller effect is responsible for limiting the gain of an amplifier at higher frequencies due to Miller capacitance between the output and input. Also, oscillations in amplifier occur due to input/output feedback.

4. How can we successfully avoid Miller effect?

a) using a common-base amplifier

b) using a common-emitter amplifier

c) by increasing the Q factor

d) by decreasing the Q factor

Answer: a

Explanation: Miller effect is responsible for the increase in equivalent input capacitance of an inverting voltage amplifier. The increase equivalent input capacitance is given by, C M = C(1 + A V ). Miller effect can be avoided by using a common-base amplifier.

5. What is the two basic specifications of a receiver?

a) sensitivity and selectivity

b) superious response and tracking

c) signal and noise

d) number of convertors and number of IFs

Answer: a

Explanation: Sensitivity and selectivity are the two key specifications for any receiver, which is used for the purpose in communication. Sensitivity is the ability of the receiver to amplify weak signals, whereas Selectivity is the ability of the receiver to reject unwanted signals.

6. Who invented the superheterodyne receivers?

a) Hertz

b) Armstrong

c) Foster

d) Seeley

Answer: b

Explanation: Superheterodyne uses frequency mixing to convert a received RF signal to a fixed IF. This method is known as heterodyning. This IF can be processed more easily than the original carrier frequency. It was invented by Armstrong.

7. Skin effect refers ________

a) the increase of wire resistance with frequency

b) the decrease of wire resistance with frequency

c) the uniform nature of wire resistance with frequency

d) the way radio signals travel across a flat surface

Answer: a

Explanation: Skin effect becomes more and more apparent as frequency increases as skin depth becomes smaller. It is due to alternating current flowing through the outer surface of conducting material. It refers to the increase of wire resistance with frequency.

8. The frequency of local oscillator ________

a) can be either below or above the RF frequency

b) is below the RF frequency

c) is above the RF frequency

d) is fixed typically at 450KHz

Answer: c

Explanation: The frequency of the local oscillator is not fixed. It is mostly above the RF frequency.

9. Phase distortion is important in ________

a) voice communication systems

b) color video receivers

c) audio receivers

d) radio reception

Answer: b

Explanation: Phase distortion is a change in the shape of the waveform. It occurs when filter’s do not have a sharp cut off frequency thus not properly filtering a wave. Thus, phase distortion is important in color video receivers.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Multitone Wideband FM”.

1. What will be the effect if we loading down a tuned-circuit amplifier?

a) it will raise the Q factor of tuned circuit

b) it will lower the Q factor of tuned circuit

c) it will multiply the Q factor by a constant

d) it will have no effect on Q factor

Answer: b

Explanation: Loading down a tuned circuit will automatically lower the Q factor of any circuit. Q factor characterizes resonator’s bandwidth relative to its center frequency. It is a measure of the performance of the resonant circuit.

2. What is the baseband bandwidth for a voice grade signal?

a) atleast 10KHz

b) atleast 5KHz

c) approximately 3KHz

d) approximately 15KHz

Answer: c

Explanation: The fixed standard baseband bandwidth for a voice grade signal is approximately close to 3KHz.

3. Miller effect can reduce the bandwidth of an amplifier.

a) True

b) False

Answer: a

Explanation: Miller effect is responsible for limiting the gain of an amplifier at higher frequencies due to Miller capacitance between the output and input. Also, oscillations in the amplifier occur due to input/output feedback.

4. What will be the reason of miller effect in BJT?

a) inductance of collector load

b) collector-to-emitter capacitance

c) base-to-emitter capacitance

d) base-to-collector capacitance

Answer: d

Explanation: Miller effect is responsible for the increase in equivalent input capacitance of an inverting voltage amplifier. The increase equivalent input capacitance is given by, C M = C(1 + A V ). In BJT, miller effect is due to base-to-collector capacitance.

5. Trimmers and padders are ________

a) two types of adjusting tools

b) small adjustable resistors

c) small adjustable inductors

d) small adjustable capacitors

Answer: d

Explanation: Trimmers and padders are the two types of small adjustable capacitors. Its capacitance can be adjusted to the required value.

6. What is the full form of IF?

a) Intermediate Frequency

b) Internal Frequency

c) Indeterminate Frequency

d) Image Frequency

Answer: a

Explanation: IF stands for intermediate frequency. It is a frequency to which a carrier wave is shifted, with the help of a mixer, as an intermediate step in transmission and reception. This IF is more suitable for executing further processes.

7. What is the full form of AGC?

a) Automatic Gain Control

b) Audio Gain Control

c) Automatic Gain Conversion

d) Active Gain Control

Answer: a

Explanation: AGC stands for Automatic Gain Control. It is closed loop feedback regulating circuit. Its purpose is to provide a controlled signal amplitude at its output, irrespective of changes in it’s input signal amplitude.

8. Sensitivity measures ________

a) weakest signal that is received at the receiver

b) strongest signal that is received at the receiver

c) weakest frequency signal that is received at the receiver

d) strongest frequency signal that is received at the receiver

Answer: a

Explanation: Sensitivity and Selectivity are two key components of any circuit. Sensitivity is used to measure the weakest signal that is received at the receiver.

9. Selectivity measures ________

a) the range of frequencies that receiver can select

b) with two signals close in frequency, the ability to select one and reject other

c) how well adjacent frequencies are separated by the demodulator

d) how well adjacent frequencies are separated in the mixer

Answer: a

Explanation: Sensitivity and Selectivity are two key components of any circuit. Selectivity is used to measure the range of frequencies that the receiver can select. Sensitivity is the ability of the receiver to amplify weak signals.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Transmission Bandwidth”.

1. What is the full form of DTMF?

a) Dual-Tone Multi frequency

b) Dual Telephony Multiple Frequency

c) Dual-Tone Minimum Frequency

d) Digital Tone Minimum Frequency

Answer: a

Explanation: DTMF is an in-band telecommunication signal. It uses the voice-frequency band over telephone lines. It was developed by Bell Systems in United States.

2. If we see practically, parallel data transmission is sent ________

a) over long distances only

b) over short distances only

c) usually over a coaxial cable

d) over a single channel

Answer: b

Explanation: In serial transmission, bits are transmitted one at a time over a single channel. In parallel transmission bits are sent simultaneously over their own individual channel. It sent data over short distances only.

3. Who invented the five-level teletype code?

a) Teletype company

b) Morkum company

c) Western Union

d) Emile Baudot

Answer: d

Explanation: Emile Baudot invented the five-level teletype code. Each character in alphabet is represented by a series of five bits.

4. What is the full form of LATA?

a) Local Access Telephone Area

b) Local Area Telephone Access

c) Local Access and Transport Area

d) Local Area Transport Access

Answer: c

Explanation: LATA stands for Local Access and Transport Area and is used in the U.S. for a geographical area covered by one or more local telephone companies. It is legally referred to as local exchange carriers.

5. The transmitter and receiver are frame-by-frame synchronized using the data bits in asynchronous transmission.

a) True

b) False

Answer: b

Explanation: In Asynchronous transmission, each character is signified by start and stop bits. Thus, the transmitter and receiver are synchronized frame-by-frame using the start and stop bits, not by data bits.

6. Why synchronous transmission is more preferred?

a) it has no start and stop bits

b) it is cheaper than asynchronous

c) it is easier to implement

d) less complex

Answer: a

Explanation: In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient. However, it is more expensive than asynchronous transmission and has highly complex circuit.

7. Which statement is true about HDLC?

a) it is not a bit-oriented protocol

b) it is a bit-oriented protocol

c) it is identical to SDLC

d) it is non-identical to SDLC

Answer: b

Explanation: HDLC is a high-level data link control. It is a bit-oriented protocol. HDLC is group of rules for transmitting data between network points.

8. What is the use of ARQ?

a) correct bit errors

b) works with a simplex channel

c) better transmission efficiency

d) can only be used in unidirectional channel

Answer: a

Explanation: ARQ is an error control method. It is used for data transmission that uses acknowledgments and inputs to achieve reliable data transmission.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “FM Stereo Multiplexing”.

1. What is the full form of PSTN?

a) Public Switched Telephone Network

b) Primary Switched Telephone Network

c) Private Switched Telephone Network

d) Protected Switched Telephone Network

Answer: a

Explanation: PSTN stands for Public Switched Telephone Network. It is the aggregate of the world’s circuit-switched telephone network. It helps in providing services for public telecommunication.

2. Which statement is true about Huffman code?

a) allow errors to be detected but not corrected

b) allow only alphanumeric data to be corrected

c) allow errors to be detected and corrected

d) allow alphanumeric data to be compressed

Answer: d

Explanation: Huffman is generally used to convert fixed length codes into variable length codes. It results in lossless compression. It allows alphanumeric data to be compressed. It does not let alphanumeric data to be corrected or error to be detected and corrected.

3. What is another name for VRC?

a) FEC

b) ARQ

c) Parity

d) Bits

Answer: c

Explanation: VRC is generally used in communication. It stands for Vertical Redundancy Check. It is same as parity.

4. What is required in SDLC to use flags?

a) Different flags at either end of a frame

b) FEC

c) Complex data bits

d) Bit stuffing

Answer: d

Explanation: SDLC stands for Software Development Life Cycle. It consists of a detailed plan describing how to develop, analyze and maintain software for it’s business value. Bit stuffing is required in it if we want to use flags.

5. Thermal noise shot noise and transit time noise is part of internal noise in communication.

a) True

b) False

Answer: a

Explanation: Internal noise in communication is the noise that gets generated within the receiver or communication system, like thermal noise, shot noise, transit time noise, partition noise and such like. External noise is that noise which is generated from an external source, that is not a part of the communication system.

6. In amplitude modulation, magnitude of side bands is 2ma times the carrier amplitude.

a) True

b) False

Answer: b

Explanation: In amplitude modulation, amplitude of the carrier wave is varied with respect to the instantaneous amplitude of the message wave to be propagated. In amplitude modulation, magnitude of side bands is 4ma times the carrier amplitude.

7. If a digital data is not used to carry characters, then it is called as ________

a) graphic control data

b) binary data

c) character data

d) floating data

Answer: b

Explanation: In a binary data user can take only two values 0’s and 1’s. So it is binary data that can’t be used for carrying characters.

8. What is the full form of POTS?

a) Private Office Telephone System

b) Public Office Telephone System

c) Primary Office Telephone System

d) Plain Old Telephone Service

Answer: d

Explanation: POTS is an analog telephone service. It stands for Plain Old Telephone Service. It is implemented over copper twisted pair wires. It is based on Bell Telephone System. POTS is used more widely due to its reliability.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Direct Method”.

1. What is the full form of ASCII?

a) American Standard Character for Information Interchange

b) American Standard Class for Information Interchange

c) American Standard Code for Information Interchange

d) Alphanumeric Standard Code for Information Interchange

Answer: c

Explanation: ASCII is the most common format for text files in computers. In an ASCII file each symbol is represented by a 7 bit binary number. In this 128 possible characters are defined.

2. The transmitter and receiver are not synchronized at all, in asynchronous transmission.

a) True

b) False

Answer: b

Explanation: In Asynchronous transmission, each character is signified by start and stop bits. Thus, the transmitter and receiver are synchronized frame-by-frame using the start and stop bits, not by data bits.

3. In synchronous transmission, receiver is able to sync with the transmitter by using ________

a) Clock bits

b) Start and Stop bits

c) CRC bits

d) Data bits

Answer: d

Explanation: In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient. Receiver and transmitter are in sync with each other by using data bits.

4. FEC stands for _________

a) Forward Error Correction

b) Fixed Error Correction

c) Forward Error Communication

d) Fixed Error Communication

Answer: a

Explanation: FEC is a method of obtaining error control in data transmission. It stands for Forward Error Correction.

5. Run-length encoding is used to ________

a) correct data

b) segregate data

c) encrypt data

d) compress data

Answer: d

Explanation: Run length encoding is a very simple form of lossless data compression in which runs of data are stored as a single value data, rather than as original run.

6. The term CD in CSMA/CD stands for _________

a) Collision Detection

b) Collision Delay

c) Compact Detection

d) Compact Delay

Answer: a

Explanation: CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. It is mostly used in early Ethernet technology for local area networking.

7. Dumb terminals are used in token-passing networks.

a) True

b) False

Answer: b

Explanation: A dumb terminal is an output that accepts data from CPU. It has no processing capabilities. Dumb terminals are used in networks that require central monitoring. Thus, dumb terminals are used for token-passing networks. However, smart terminals to exist which has its own processor.

8. In networks, long messages are divided into “chunks” called __________

a) packets

b) bits

c) parts

d) tokens

Answer: a

Explanation: For any long message to be transmitted, it is first divided into many small parts called packets. Individual packets belonging to a long message may arrive out of order at the destination.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Variation Method”.

1. What is the full form of LF?

a) Line Feed

b) Link Feed

c) Line Forward

d) Link Forward

Answer: a

Explanation: Line feed means moving one line forward. It is basically a control character, coded upto 10 decimal places, respective to ASCII Character Set.

2. In synchronous transmission, frames are about the same length as in asynchronous transmission.

a) True

b) False

Answer: b

Explanation: In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient. However, it is more expensive than asynchronous transmission and has highly complex circuit.

3. What is the full form of UART?

a) Universal Asynchronous Receiver Transmitter

b) Universal Automatic Receiver Transmitter

c) Unaltered Asynchronous Receiver Transmitter

d) Unaltered Automatic Receiver Transmitter

Answer: a

Explanation: UART is a computer hardware device. It is mainly used for asynchronous serial communication. It is used in modules like Bluetooth etc. It stands for Universal Asynchronous Receiver Transmitter, where the receiver and transmitter communicate in absence of any clock pulse.

4. To maintain synchronization in synchronous transmission __________

a) long strings of 1s and 0s must not be allowed

b) transmission must stop periodically

c) clock circuits must be precisely adjusted

d) channel must be noise free

Answer: a

Explanation: In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient. However, it is more expensive than asynchronous transmission and has highly complex circuit. To maintain synchronization long strings of 1s and 0s are not allowed.

5. CRC stands for __________

a) Cyclic Redundancy Check

b) Cyclic Repeat Check

c) Cyclic Redundancy Character

d) Cyclic Redundancy Code

Answer: a

Explanation: CRC is an error detecting code. It is generally used in digital network. It was invented by W. Wesley Peterson. CRC stands for Cyclic Redundancy Check.

6. What do you understand by the term Internet?

a) a network of networks

b) a very large client-server network

c) a very large CSMA/CD network

d) local area network

Answer: a

Explanation: Internet is a global network providing us a variety of information. It is a network of networks that consists of public, private, business, and government networks of local to a global scope.

7. Which statement is correct about circuit-switched network?

a) each channel can carry only one data stream

b) usually uses a bus topology

c) usually uses a star topology

d) implemented at network layer

Answer: a

Explanation: In circuit switching a circuit is applied for the duration of the transmission. Its example is a telephone. In it each channel can carry only one data stream.

8. When two or more PCs try to access a baseband network cable at the same time, it is called ________

a) contention

b) collision

c) excess traffic

d) switching

Answer: a

Explanation: Contention is a term of networks, used when two or more PCs try to access a baseband network cable at the same time.

9. When two PCs send data over a baseband network cable at the same time, it is called ________

a) contention

b) collision

c) excess traffic

d) switching

Answer: b

Explanation: Collision is a term of networks, used when two PCs send data over a baseband network cable at the same time.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Foster Seely”.

1. What is the full form of SDLC?

a) Synchronous Data Link Character

b) Synchronous Data Line Control

c) Synchronous Data Line Character

d) Synchronous Data Link Control

Answer: d

Explanation: SDLC stands for Synchronous Data Link Control. It is a layer 2 protocol for IBM’s Systems Network Architecture. It supports multipoint links as well as error-correction. It helps in the proper flow of data to different levels.

2. Mostly LANs are based on Ethernet.

a) True

b) False

Answer: a

Explanation: LAN stands for Local Area Network and is a computer network that interconnects computers within a limited area. Most LANs are based on Ethernet only. It can also connect devices through wireless link to a server.

3. CSMA stands for _________

a) Carrier Sense Multiple Access

b) Client Sense Multiple Access

c) Carrier Server Multiple Access

d) Client Server Multiple Access

Answer: a

Explanation: CSMA stands for Carrier Sense Multiple Access. It is a media access control protocol. In it, a node verifies the absence of other traffic before transmission.

4. What we called each computer in a network?

a) node

b) circuit

c) hub

d) switch

Answer: a

Explanation: In networks, each connected computer is seen as a node.

5. Which network never experienced a collision?

a) CSMA

b) Token-passing

c) LAN

d) All networks have collision at some point

Answer: b

Explanation: Token passing is a channel access method. In it, a signal which is seen as a token is passed between nodes to authorize that node to communicate. Token passing never experiences any type of collisions.

6. What is the effect of too many collisions in any network?

a) network slows down

b) network crashes

c) cable overheats

d) data gets lost

Answer: a

Explanation: If a network receives too many collisions, it directly affects its connected nodes. Due to which the network finally slows down.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “ZCD”.

1. MAU stands for __________

a) Multiple Access Unit

b) Multi-station Access Unit

c) Multiple Auxiliary Unit

d) Multi-station Auxiliary Unit

Answer: b

Explanation: MAU stands for the Multi-station Access Unit. It acts as a hub that connects a group of computers to a token ring local area network.

2. Packet switching is based on ________

a) switched circuits

b) un-switched circuits

c) store-and-forward

d) real time delivery

Answer: c

Explanation: Packet switching is a method of grouping data transmitted over a network into packets. It has two modes of operation: Connectionless Packet Switching and Connection-Oriented Packet Switching. It is based on a store and forward algorithm.

3. What is used for setting up a virtual circuit?

a) frame

b) network

c) link

d) hub

Answer: b

Explanation: For the creation of any virtual circuit, a network is must required.

4. Which modulation is used in high frequency radio-teletype systems?

a) QAM

b) ASK

c) PSK

d) FSK

Answer: d

Explanation: Frequency Shift Keying is a type of frequency modulation. In it, data is transmitted through discrete frequency changes of a carrier signal. It is highly used in frequency radio-teletype systems.

5. When we use TDMA instead of TDM?

a) when signals come from different sources

b) when all the signals come from same source

c) when all the signals contain the same information

d) when all the signals contain different information

Answer: a

Explanation: If all the signals comes from different types of sources, then it is better to use TDMA instead of TDM.

6. The effect of frequency on the resistance of a wire is called ________

a) skin effect

b) I2R loss

c) ohmic effect

d) threshold effect

Answer: a

Explanation: Skin effect becomes more and more apparent as frequency increases as skin depth becomes smaller. It is due to alternating current flowing through the outer surface of conducting material. It refers to the increase of wire resistance with frequency.

7. The electric and magnetic field of a radio wave are perpendicular to each other.

a) True

b) False

Answer: a

Explanation: The statement is correct that both fields are perpendicular to each other. They are also perpendicular to the direction of propagation.

8. Which polarization is possible for an electromagnetic wave?

a) vertical

b) circular

c) horizontal

d) can be vertical or horizontal or circular

Answer: d

Explanation: In electromagnetic waves, both electric and magnetic fields are present. Polarization states the orientation of electric flux lines in EM field. Thus it can be vertically polarized or horizontally or circularly polarized.

9. On which factor dominant mode of a waveguide depends?

a) shape

b) power

c) direction

d) bandwidth

Answer: a

Explanation: A waveguide is something that guides waves, such as electromagnetic wave or sound with minimum loss of energy. The dominant mode of a waveguide depends on the shape of the waveguide.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Reactance Modulator”.

1. Which is the dominant mode for a rectangular waveguide?

a) TE 01

b) TM 01

c) TE 10

d) TM 10

Answer: c

Explanation: Rectangular waveguides are the earliest form of transmission lines. It supports TM and TE mode, which stands for Transverse Magnetic waves and Transverse Electric waves respectively, but it does not support TEM, Transverse Electromagnetic waves, mode. A rectangular waveguide can’t propagate below some certain frequency. The dominant mode for it is TE 10 mode.

2. EIRP stands for _________

a) Effective Isotropic Radiated Power

b) Effective Isotropic Reflected Power

c) Effective Isotropic Refracted Power

d) Effective Isotropic Regulated Power

Answer: a

Explanation: ERIP stands for Effective Isotropic Radiated Power. It is basically the output power when a signal is concentrated into a smaller area with the help of the antenna.

3. Characteristic impedance of a cable depends only on the resistance per foot of the wire used.

a) True

b) False

Answer: b

Explanation: Characteristic Impedance is the ratio of voltage amplitude to current amplitude of a propagating electromagnetic wave. The characteristic impedance of a cable depends on the inductance per foot and the capacitance per foot.

4. When calculating the maximum number of users, limiting factor in FDM is ___________

a) bandwidth of each signal

b) type of each signal

c) amplitude of each signal

d) length of the channel

Answer: a

Explanation: When calculating the maximum users in frequency division multiplexing, the bandwidth of each transmitting signal must be observed very carefully and thus it is also the limiting factor in FDM.

5. CDMA stands for Carrier Division Multiple Access.

a) True

b) False

Answer: b

Explanation: CDMA stands for Code Division Multiple Access. It refers to any protocol that is used in second generation and third generation wireless communication.

6. QPSK symbol contains ________

a) a byte

b) 4 bits

c) a dibit

d) 8 bits

Answer: c

Explanation: QPSK stands for Quadrature Phase Shift Keying which is a digital signal modulation scheme. In QPSK, only two bits are transmitted per symbol. It represents 00, 01, 10, 11

7. What is the full form of ATM?

a) Asynchronous Transfer Mode

b) Asynchronous Transmission Mode

c) Automatic Transmission Mode

d) Automatic Transfer Mode

Answer: a

Explanation: ATM stands for Asynchronous Transfer Mode. It uses asynchronous time division multiplexing and encodes data into small but fixes size packets.

8. Who invented the Ethernet?

a) IBM

b) Xerox

c) Intel

d) Cisco

Answer: b

Explanation: Ethernet is a computer technology mostly used in LANs. LAN connects devices sharing a common network or linked by the same server. Ethernet was invented by Xerox.

9. MAN stands for ________

a) Metropolitan Access Network

b) Metropolitan Area Network

c) Multiple Area Network

d) Multiple Access Network

Answer: b

Explanation: MAN stands for Metropolitan Area Network. It interconnects computers that are under a fixed geographic area larger than that covered by LAN but smaller than the area covered by WAN.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Varactor Diode”.

1. Which layer is used for detection of bad frames in wide area network?

a) frame layer

b) link layer

c) physical layer

d) session layer

Answer: b

Explanation: Wide area network covers a long geographical area and thus it also has least connected devices. Link layer is used in WAN for detection of bad frames.

2. TEM stands for Transmitted Electromagnetic wave.

a) True

b) False

Answer: b

Explanation: TEM stands for Transverse Electromagnetic wave. Since both electric and magnetic field are transverse to the direction of wave propagation.

3. What is the reason of attenuation in free space?

a) decrease in energy per square meter due to expansion

b) decrease in energy per square meter due to compression

c) losses in upper atmosphere due to expansion

d) losses in upper atmosphere due to compression

Answer: a

Explanation: In free space, the basic reason of attenuation is the decrease in energy per square meter. It generally happens due to expansion.

4. What is the range of UHF?

a) below the microwave range

b) above the microwave range

c) same as the microwave range

d) it does not include the microwave range in any way

Answer: a

Explanation: Ultra high frequency is the ITU designation for radio frequencies that lies under 300MHz to 3 GHz i.e. its range is below the microwave range.

5. Striplines and microstrips are used to __________

a) couple sections of waveguide

b) couple waveguides to antennas

c) couple components on a circuit board

d) couple electromagnetic waves in an order

Answer: c

Explanation: The main use of Striplines and microstrips in any circuit is to couple components on a circuit board.

6. What is the another term used for a single microwave link?

a) section

b) hop

c) link

d) skip

Answer: b

Explanation: Microwave link is a communication system that uses a beam of radio waves in the microwave frequency range. Hop is also used in places of single microwave link.

7. In digital microwave systems, additional repeaters increase the ________

a) selectivity

b) noise level

c) jitter

d) sensitivity

Answer: c

Explanation: In telecommunication, jitter can be seen as a deviation from true periodicity of a presumably periodic signal. Higher level of jitter are more likely to occur on either slow or heavily congested link. In any circuit, adding additional repeaters finally increase the jitter only.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Frequency Translation”.

1. FSK stands for ________

a) Frequency Segregation Keying

b) Frequency Section Keying

c) Frequency Signal Keying

d) Frequency Shift Keying

Answer: d

Explanation: FSK stands for Frequency Shift Keying. In FSK, information is transmitted through discrete frequency changes in the carrier signal.

2. When analyzing a transmission line, its inductance and capacitance are considered as _________

a) distributed

b) lumped

c) equal reactances

d) equal impedances

Answer: a

Explanation: For a transmission line, inductance and capacitance are two components that are considered as distributed.

3. What effect will be seen on the resistance of a wire if we increase the frequency?

a) it will also increase

b) it starts to decrease

c) it will remain same

d) it starts changing periodically

Answer: a

Explanation: Skin effect becomes more and more apparent as frequency increases as skin depth becomes smaller. It is due to alternating current flowing through the outer surface of conducting material. It refers to the increase of wire resistance with frequency.

4. What is speed of radio waves in free space?

a) 3 x 10 6 m/s

b) 3 x 10 9 m/s

c) 300 x 10 6 m/s

d) 300 x 10 9 m/s

Answer: c

Explanation: he speed of radio waves in free space is same as the speed of light which is 3 x 10 8 m/s. It cal also be written as 300 x 10 6 .

5. An antenna has “gain” as compared to ________

a) Helical antenna

b) Marconi antenna

c) Vertically polarized radiator

d) Isotropic radiator

Answer: d

Explanation: Isotropic radiator is considered as an ideal antenna. So all the gains of any antenna is estimated by comparing with it only.

6. Ground waves are most effective when _________

a) it is above about 20MHZ

b) it is below about 3MHz

c) it is at microwave frequencies

d) usually in the UHF range

Answer: b

Explanation: Ground wave is generally preferred for long distance communication using frequencies that are below 3MHz. It can be used for short distance communication by using frequencies between 3 and 30MHZ.

7. The microwave frequency range is considered to start at ________

a) 1 GHz

b) 10 GHz

c) 100 GHz

d) 5 GHz

Answer: a

Explanation: Microwave frequency range is considered to be start at 1 GHz. It is standard and fixed.

8. What is the approximate reliability of a microwave system?

a) 90%

b) 99%

c) 99.99%

d) 90.99%

Answer: c

Explanation: Microwave system is mostly known for its reliability. Its reliability is of the order of 99.99%.

9. Which modulation is used by a microwave system?

a) FM

b) SSB

c) QAM

d) Either FM or SSB or QAM

Answer: d

Explanation: Microwave system is used for point-to-point communication links, which is the communication between two nodes. It can either use frequency modulation or single sideband modulation or quadrature modulation.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Frequency Division Multiplexing”.

1. TDMA stands for ________

a) Time Division Multiple Access

b) Time Domain Multiple Access

c) Time Division Mutual Access

d) Time Domain Mutual Access

Answer: a

Explanation: TDMA stands for Time Division Multiple Access. It can be seen as a channel access method for shared-medium networks.

2. Which term is used when signals move from one line to another?

a) path switching

b) space switching

c) line switching

d) cross-point switching

Answer: b

Explanation: Space switching is the used term for signals moving from one line to another.

3. PSK stands for Pulse Shift Keying.

a) True

b) False

Answer: b

Explanation: PSK stands for Phase Shift Keying. It is a modulation scheme that conveys information by changing the phase of carrier.

4. Which term is used for moving PCM samples from one time slot to another?

a) time switching

b) space switching

c) phase switching

d) frequency switching

Answer: a

Explanation: Time switching is the used term for moving PCM samples moving from one time slot to another.

5. Power can be coupled into or out of a waveguide with a magnetic field probe.

a) True

b) False

Answer: b

Explanation: A waveguide is a line through which electromagnetic waves are passed for various use. Power can be coupled into or out of a waveguide not only with a magnetic field probe. It can also be coupled with an electric field probe. It can also be coupled through a hole in the waveguide.

6. What is the full form of LOS?

a) Level Of Signal

b) Line Of Sight

c) Loss Of Signal

d) Level Of Sight

Answer: b

Explanation: Line Of Sight is a line between two points. It is a straight path between a transmitting antenna and a receiving antenna.

7. How we can define the satisfactory performance of an analog microwave system?

a) carrier to noise ratio that exceeds a given value

b) carrier to noise ratio that is below a given value

c) an ERP value that exceeds a given value

d) an ERP value that is below a given value

Answer: a

Explanation: We can measure performance of an analog microwave system by calculating the carrier to noise ratio that exceeds a given value. It gives the signal to noise ratio.

8. RGB stands for ________

a) Red Green Brown

b) Red Green Black

c) Red Gold Blue

d) Red Green Blue

Answer: d

Explanation: RGB stands for Red Green Blue. It is an additive color model in which red, green and blue light intensity and different shades are added together in various ways to reproduce a broad variety of colors.

9. How many lines are there in an NTSC signal?

a) 1024

b) 1856

c) 625

d) 525

Answer: d

Explanation: NTSC stands for National Television System Committee. In NTSC, it is standardized fixed that it has total 525 lines.

10. Luminance refers to ________

a) contrast

b) diffusion

c) brightness

d) aperture

Answer: c

Explanation: Luminance refers to brightness. It is a photometric measure of luminous intensity per unit area of light travelling in a given direction.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Practicality of Antenna”.

1. TDR stands for ________

a) Total Distance of Reflection

b) Time Domain Response

c) Time Domain Reflectometry

d) Time Delay Ratio

Answer: c

Explanation: TDR stands for Time Domain Reflectometer. It is an electronic instrument that uses time domain reflectometry to locate faults.

2. The number of circular polarization modes is _________

a) 1

b) 2

c) many

d) 3

Answer: b

Explanation: In circular polarization either the electric or magnetic vector executes a circle which is further perpendicular to path of propagation. There are two circular polarization modes.

3. Which is the dominant for a circular waveguide?

a) TE 01

b) TM 01

c) TE 11

d) TM 11

Answer: c

Explanation: Circular Waveguide supports TM and TE mode, which stands for Transverse Magnetic waves and Transverse Electric waves respectively, but it does not support TEM, Transverse Electromagnetic waves, mode. A rectangular waveguide can’t propagate below some certain frequency. The dominant mode for it is TE 11 mode.

4. The characteristic impedance of a waveguide is fixed.

a) True

b) False

Answer: b

Explanation: Characteristic Impedance is the ratio of voltage amplitude to current amplitude of a propagating electromagnetic wave. The characteristic impedance of a waveguide is not fixed. It depends on the frequency it carries. It also depends on the longer dimension of its cross section.

5. Too much antenna gain causes ________

a) jitter

b) high sensitivity

c) a very wide microwave beam

d) a very narrow microwave beam

Answer: d

Explanation: Measurement of gain of any antenna takes place by comparing it with the value of isotropic antenna. Too much gain in antenna can cause a very narrow microwave beam.

6. NTSC stands for ________

a) National Television Systems Committee

b) National Television Security Committee

c) National Television Systems Council

d) National Television Security Council

Answer: a

Explanation: NTSC stands for National Television Systems Committee. It is mostly used in North America. It was responsible for developing a set of protocols for television broadcast transmission and reception in the United States. Its specifications was drawn up by EIA.

7. NTSC specifications was drawn up by ________

a) FCC

b) IBM

c) Cisco

d) EIA

Answer: d

Explanation: NTSC stands for National Television Systems Committee. It is mostly used in North America. It was responsible for developing a set of protocols for television broadcast transmission and reception in the United States. Its specifications was drawn up by EIA.

8. What is the aspect ratio of a standard TV receiver?

a) 3:4

b) 525:625

c) 625:525

d) 4:3

Answer: d

Explanation: Aspect ratio is an image projection attribute that describes the proportional relationship between the width of an image and its height. Most common video-graphic aspect ratio is 4:3.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Reduction of Noise”.

1. Luminance is measured in ________

a) Decibels

b) IRE units

c) Lumins

d) NTSC units

Answer: b

Explanation: Luminance refers to brightness. It is a photometric measure of luminous intensity per unit area of light travelling in a given direction. It is measured in IRE units.

2. The maximum luminance level is called ________

a) max white

b) peak white

c) all white

d) full white

Answer: b

Explanation: Luminance refers to brightness. It is a photometric measure of luminous intensity per unit area of light travelling in a given direction. It is measured in IRE units. The maximum luminance level is called peak white.

3. Which term is used for defining high and low points of a satellite’s orbit?

a) crest and trough

b) apogee and perigee

c) uplink and downlink

d) peak and sink

Answer: b

Explanation: Apogee and Perigee are respectively the terms used for defining high and low points of a satellite’s orbit.

4. What is the power order of power level for an earth station to transmit to a satellite?

a) 104 watts

b) 103 watts

c) 100 watts

d) 101 watts

Answer: b

Explanation: The standard power level of an earth station to transmit to a satellite is of the order of 103 Watts.

5. What is the full form of DBS?

a) direct broadcast satellite

b) decibels of signal

c) direct beam signal

d) direct broadcast signal

Answer: a

Explanation: DBS stands for direct broadcast satellite. In Direct Broadcast Satellite subscribers receives signal directly from geostationary satellite.

6. RCC stands for __________

a) Radio Common Carrier

b) Radio Central Carrier

c) Radio Control Carrier

d) Radio Cell Carrier

Answer: a

Explanation: RCC stands for Radio Common Carrier. It was introduced in 60’s. Like a radio it can also transmit voice communication through a push to talk system. But it used a public telephone network and has its own telephone number.

7. Current PCs are referred as __________

a) first-generation

b) second-generation

c) third-generation

d) fourth-generation

Answer: b

Explanation: Current PCs in today’s time are referred as second generation.

8. ISM stands for _________

a) IEEE Standard Message

b) Industrial, Scientific and Messaging

c) Industrial, Scientific and Medical

d) IEEE Secure Message

Answer: c

Explanation: ISM stands for Industrial, Scientific and Medical. In it some radio frequencies are only used for Industrial, Scientific and Medical purposes not for telecommunications purpose. Bluetooth uses ISM band.

9. Bluetooth uses ________

a) CDMA

b) Frequency hopping

c) QPSK

d) QAM

Answer: b

Explanation: Bluetooth is a wireless technology. It is used for exchanging data over short distances. It usually uses frequency hopping, in which the transmitter changes the carrier frequency with respect to a specific pattern.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Narrowbanding”.

1. Which band is used by Bluetooth in mobiles?

a) VHF band

b) UHF band

c) ISM band

d) HF band

Answer: c

Explanation: Bluetooth is wireless technology. It is used for exchanging data over short distances. It usually uses frequency hopping. It uses ISM band.

2. BSS stands for ________

a) Basic service Set

b) Basic service System

c) Bluetooth service Set

d) Bluetooth service System

Answer: a

Explanation: BBS stands for Basic service Set. It is a term used to describe the collection of stations which may communicate with each other within an 802.11 network. It is used for telecommunication services.

3. What do you understand by the term CAPCODE?

a) an encryption scheme

b) an addressing scheme

c) an error-detection scheme

d) a decryption scheme

Answer: b

Explanation: CAPCODE is only used as an addressing scheme.

4. The “forward” PCs channel is ________

a) from the base to mobile

b) from the mobile to base

c) from mobile to mobile

d) from base to base

Answer: a

Explanation: If the PCs channel is forwarded then it means that signal goes from the base to the mobile.

5. What is the full form of MSC?

a) Mobile Service Cellular

b) Mobile Switching Center

c) Mobile Switching Control

d) Mobile Servicing Council

Answer: b

Explanation: MSC stands for Mobile Switching Center. It is a 2G core network element that controls the network switching subsystem elements.

6. LNA stands for __________

a) low noise amplifier

b) low noise amplification

c) low narrow amplification

d) low narrow amplifier

Answer: a

Explanation: LNA stands for low noise amplifier. It is used to amplify possibly weak signals such as those as received by an antenna.

7. The “payload” in a communication satellite consists of _________

a) power amplifiers

b) batteries

c) transponders

d) transducers

Answer: c

Explanation: Transponders works as the payload in any communication. It uses for receiving a radio signal and then automatically transmits a different signal.

8. What is the height of the geosynchronous orbit above the equator?

a) 3,578km

b) 35,780km

c) depends on escape velocity

d) depends on satellite velocity

Answer: b

Explanation: The height of the geosynchronous orbit above the equator is approximately 35,780 km.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Phase Comparator”.

1. The velocity required to stay in orbit is ________

a) constant

b) infinite

c) lower close to the earth than far from the earth

d) higher close to the earth than far from the earth

Answer: d

Explanation: The velocity in orbit must be higher close to the earth than far from the earth. Then only components can stay in orbit.

2. An antenna is adjusted by adjusting the two “look angles” called _________

a) coverage and elevation

b) declination and elevation

c) azimuth and declination

d) azimuth and elevation

Answer: d

Explanation: Azimuth and Elevation are two look angles of any antenna. So any antenna can be adjusted by adjusting these two angles properly.

3. PCS stands for ________

a) Portable Control Service

b) Personal Communication Systems

c) Personal Control Signal

d) Portable Communication Systems

Answer: b

Explanation: PCs stands for Personal Communication Systems. It is a wireless phone service similar to cellular service but emphasizing on personal service and extending mobility.

4. What is the full form of MIN?

a) Multistage Interconnection Network

b) Mobile Identification Number

c) Maximum In-band Noise

d) Minimum In-band Noise

Answer: b

Explanation: MIN stands for Mobile Identification Number. It refers to the 10 digit unique number that a wireless carrier uses to identify a mobile phone.

5. Which term is used for voice channels, in GSM?

a) traffic channels

b) noise channels

c) receiver channels

d) transmitter channels

Answer: a

Explanation: Traffic channel is the term used for voice channels, in GSM.

6. Pagers use _________

a) VHF band

b) UHF band

c) Both VHF and UHF bands

d) HF band

Answer: c

Explanation: A pager is a telecommunication device that receives alert signals and short messages. It can use both UHF and VHF band.

7. What is the approximate IEEE specification covering wireless LANs?

a) 802.13

b) 802.12

c) 802.11

d) 802.10

Answer: c

Explanation: 802.11 is the approximate IEEE specification for covering wireless LANs. LAN stands for Local Area Network, which connects multiple devices sharing a common network or being connected to the same server.

8. TDD stands for _________

a) Time Division Duplex

b) Time Delayed Duplex

c) Telecommunication Display Device

d) Time Definite Delivery

Answer: a

Explanation: TDD stands for Time Division Duplex. It refers to duplex communication links where uplink is separated from downlink. They are separated by allocating them different time slots in the same frequency band.

This set of Analog Communications Quiz focuses on “Bandwidth Requirement for PAM Transition”.

1. A Bluetooth “piconet” has ________

a) 1 node

b) 2 nodes

c) 2 to 8 nodes

d) 2 to 16 nodes

Answer: c

Explanation: Bluetooth is wireless technology. It is used for exchanging data over short distances. It usually uses frequency hopping. In frequency hopping, the transmitter changes the frequency with respect to a certain hopping pattern. A Bluetooth piconet has 2 to 8 nodes.

2. POCSAG stands for ________

a) Post Office Code Standardization Advisory Group

b) Post Office Common Standardization Advisory Group

c) Pager Office Code Standardization Advisory Group

d) Pager Office Common Standardization Advisory Group

Answer: a

Explanation: POCSAG stands for Post Office Code Standardization Advisory Group. It formulates a paging protocol, known as POCSAG protocol. This protocol is asynchronous in nature and is used to deliver data to pagers.

3. Who invented the technology CDMA?

a) Qualcomm

b) Bell Labs

c) SAP Labs

d) AT&T

Answer: a

Explanation: CDMA stands for Code Division Multiple Access. CDMA was invented by Qualcomm. CDMA is a channel access method used by various radio communication technologies. It is a kind of multiplexing where various signals uses the same transmission channel in a more optimized way.

4. AMPS was designed for POTS only.

a) True

b) False

Answer: b

Explanation: AMPS  was designed for POTS  as well as for voice. It was also designed for the use built into an automobile.

5. What is the full form of MTSO?

a) Minimum Transmitted Signal Output

b) Maximum Transmitted Signal Output

c) Mobile Telephone Switching Office

d) Mobile Telephone Signal Office

Answer: c

Explanation: MTSO stands for Mobile Telephone Switching Office. It contains the switching equipment for routing mobile phone calls. It is a mobile version of PSTN .

6. AMPS stands for ________

a) American Mobile Phone System

b) Advanced Mobile Phone Service

c) American Mobile Phone Service

d) Advanced Mobile Phone System

Answer: b

Explanation: AMPS stands for Advanced Mobile Phone Service. It is a standard system for analog signal cellular telephone service in the United States and in other countries. It is based on the electromagnetic radiation spectrum stated by FCC .

7. “Station-keeping” refers to ___________

a) antenna maintenance

b) power level adjustments

c) orbital adjustments

d) range of frequencies

Answer: c

Explanation: Station keeping refers to the orbital adjustments, whereas Bandwidth refers to range of frequencies.

8. The area on the earth that is covered by a satellite is called __________

a) plate

b) footprint

c) downlink

d) earth station

Answer: b

Explanation: Footprint refers to the area covered by a satellite on earth. Transmission from earth to satellite is called uplink and transmission from satellite to earth is called downlink. Earth station is used to deliver signals obtained from satellites.

This set of Analog Communications Problems focuses on “Noise in Pulse Modulated System”.

1. Fiber-optic cable can be used to connect a transmitter to an antenna.

a) True

b) False

Answer: b

Explanation: A fiber-optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages. Fiber-optic cable cannot be used to connect a transmitter with an antenna. An antenna is a collection of conductors is connected electrically to the transmitter.

2. Scattering causes _________

a) refraction

b) loss

c) dispersion

d) reflection

Answer: b

Explanation: In scattering, particles are forced to deviate from a straight trajectory due to non-uniformities in the medium. Thus, it causes loss of data.

3. The loss in single-mode fiber optic cable due to the glass is about ________

a) 40 dB per km

b) 0.4 dB per km

c) zero

d) 100 dB per km

Answer: b

Explanation: A duplex arrangement is a cordless telephone that uses separate frequencies for transmission in base and portable units. In duplex communication, sender and receiver can interact simultaneously while in half-duplex, sender and receiver communicates one at a time.

4. The loss in single-mode fiber optic cable due to the splice is about ________

a) 0.2 dB per km

b) 0.02 dB per km

c) 0.0002 dB per km

d) 2 dB per km

Answer: b

Explanation: A fiber-optic cable consist of a bundle of glass threads, each of which is capable of transmitting messages. The loss in single-mode fiber optic cable due to the splice is about 0.02 dB per km. In single mode fiber optical cable, only a single light ray is transmitted.

5. The loss in single-mode fiber optic cable due to the connector is about ________

a) 0.2 dB per km

b) 0.02 dB per km

c) 0.0002 dB per km

d) 2 dB per km

Answer: a

Explanation: A fiber-optic cable consist of a bundle of glass threads, each of which is capable of transmitting messages. The loss in single-mode fiber optic cable due to the connector is about 0.2 dB per km. In single mode fiber optical cable, only a single light ray is transmitted.

6. What is the full form of FITL ________

a) Fiber Input Timing Loss

b) Fibre Impedance To The Loop

c) Fiber Input Timing Loop

d) Fiber In The Loop

Answer: d

Explanation: FITL stands for Fiber In The Loop. It is a system used to upgrade PSTN  network Local loop. PSTN consists of all circuit-switched telephone in the whole world.

7. Adding bits to synchronize one digital signal to another is called _________

a) WDM

b) TDM

c) Bit stuffing

d) Bit synchronization

Answer: c

Explanation: Bit stuffing is the addition of bits for synchronization of one digital signal to another. It is mainly used in the transmission process of the network and communication protocols.

8. What is represented by “Figure Of Merit”?

a) how much noise is in the channel

b) how much noise is in the communication system

c) how much noise an amplifier adds to the signal

d) signal to noise ratio in dB

Answer: c

Explanation: Figure Of Merit is a measure of efficiency or effectiveness. It basically represents that how much noise is being added by an amplifier to the signal. However, the signal to noise ratio is the measure of the amount of signal present with respect to the surrounding noise.

9. In a balanced mixer, the output _________

a) contains equal amount of all input frequencies

b) does not contain the input frequencies

c) contains the input frequencies

d) is a non-linear mixture of input signals

Answer: b

Explanation: Mixer is a device that multiples two signals. In a balanced mixer, the output does not contain the input frequencies. And if it contains the frequency then mixer becomes imbalanced.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “PWM”.

1. What is the full form of SONET?

a) Synchronous Optical Network

b) Standard Optical Network

c) Secret Optical Network

d) Service Optical Network

Answer: a

Explanation: SONET stands for Synchronous Optical Network. SONET transfers multiple digital bit streams in a synchronized way over optical fiber using lasers.

2. VFO stands for ________

a) Voltage Feedback Oscillator

b) Variable Feedback Oscillator

c) Voltage Frequency Oscillator

d) Variable Frequency Oscillator

Answer: d

Explanation: VFO stands for Variable Frequency Oscillator. VFO is an oscillator whose frequency can be tuned over some range. It is a necessary component in any tunable radio. It is mostly used in superheterodyne receivers.

3. What is used in Hartley oscillator?

a) a piezoelectric crystal

b) two resistor divider

c) a two-capacitor divider

d) a tapped inductor

Answer: d

Explanation: In Hartley oscillator, the oscillation frequency is determined by a tuned circuit consisting of capacitors and inductors. Thus, it is an LC oscillator whose frequency can be varied. Hartley oscillator was invented in 1915.

4. The conditions for sinusoidal oscillation from an amplifier are called _________

a) Loop-gain criteria

b) Hartley criteria

c) Biasing criteria

d) Barkhausen criteria

Answer: d

Explanation: The conditions for sinusoidal oscillation from an amplifier are called Barkhausen criteria. It was invented in 1921.

5. Which parts of a sinusoidal carrier can be modulated?

a) only amplitude

b) only frequency

c) its amplitude, frequency and direction

d) its amplitude, frequency and phase angle

Answer: d

Explanation: If the carrier wave is sinusoidal, then we can vary its amplitude, frequency, and phase in proportion with the wave which is transmitted.

6. The power density of a flicker noise is _________

a) low at high frequencies

b) greater at low frequencies

c) greater at high frequencies

d) low at low frequencies

Answer: b

Explanation: Flicker noise is a form of noise that exhibits an inverse frequency power density curve. It usually occurs at low frequencies. Its power density is greater at low frequencies.

7. Power above the minimum required by an optical receiver is called ________

a) phase margin

b) system margin

c) excess gain

d) gain margin

Answer: b

Explanation: System margin is the term used when the applied power is above the minimum required power by an optical receiver.

8. What is the full form of DWDM?

a) Dense Wavelength Division Multiplexing

b) Dense Wavelength Division Modulation

c) Directed Wavelength Division Multiplexing

d) Directed Wavelength Division Modulation

Answer: a

Explanation: DWDM stands for Dense Wavelength Division Multiplexing. In DWDM, each signal has its own separated wavelength.

9. FTTC stands for ________

a) Fiber To The Curb

b) Fiber Telephone Transmission Cable

c) Fiber Transmission Timing Cable

d) Fiber Telephone Timing Cable

Answer: a

Explanation: FTTC stands for Fiber To The Curb. It is a replacement of Plain Old Telephone Service  that we see in our neighborhood.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Baseband Channel”.

1. If we compared to the core, the index of refraction of cladding must be ________

a) same

b) greater

c) less

d) infinite

Answer: c

Explanation: Core of a optical fiber is a cylinder of glass or plastic that runs along the fiber’s length. The core is surrounded by a medium with a lower index of refraction, called cladding.

2. What is used in making single-mode fiber?

a) plastic

b) glass

c) copper

d) aluminium

Answer: b

Explanation: Single mode fiber is usually made up of glass. Single-mode fiber is designed to carry light directly down the fiber.

3. A single-mode cable does not suffer from?

a) chromatic dispersion

b) waveguide dispersion

c) modal dispersion

d) material dispersion

Answer: c

Explanation: Modal dispersion can’t be seen in a single mode cable. It is used for transmission of a single ray.

4. ISI stands for ________

a) Inter Symbol Interference

b) Inter Signal Interference

c) Inter System Interference

d) Inter Sound Interference

Answer: a

Explanation: ISI stands for Inter Symbol Interference. It is a form of distortion of a signal in which one symbol gets interfered with different signals.

5. FDDI stands for __________

a) Fiber Digital Data Interface

b) Fiber Digital Delay Interface

c) Fiber Distributed Data Interface

d) Fiber Distributed Delay Interface

Answer: c

Explanation: FDDI stands for Fiber Distributed Data Interface. It is used for data transmission on optical fiber lines in a LAN that can also extend in range upto 200km. LAN is a local area network that connects various devices belonging to the same network.

6. What you understand by the term Soliton?

a) it is a defect in the glass

b) it is a type of particle

c) it is a type of pulse

d) it is a type of optical fibre

Answer: c

Explanation: Soliton is a self-reinforcing solitary wave packet that maintains its shape, when it propagates with a constant velocity. So, it is a type of pulse only.

7. Signal to noise ratio is calculated as signal voltage divided by noise voltage.

a) True

b) False

Answer: b

Explanation: Signal to Noise ratio is the measure of signal present with respect to the surrounding noise. Signal to noise ratio is calculated as signal power divided by noise power.

8. Which statement is true about varacter?

a) it is a diode

b) it is a voltage-controlled oscillator

c) it is used in tuned circuits

d) it is a diode used in tuned circuit and also has a voltage-controlled capacitor

Answer: d

Explanation: Varacter is a diode used in communication for tuning the circuit. It is also known as voltage controlled capacitor .

9. A frequency synthesizer is _________

a) A VCO phase locked to a reference frequency

b) A VFO phase locked to a reference frequency

c) A fixed RF generator

d) A variable RF generator

Answer: a

Explanation: Frequency synthesizer generates a range of frequencies from a single reference frequency.

10. Why CSMA/CD network has a minimum length for packets?

a) to increase the data rate

b) to decrease the data rate

c) to prevent packets from reaching all other nodes

d) to make sure that all other nodes hear a collision in progress

Answer: d

Explanation: CSMA/CD is a media access control used in early Ethernet technology for local area networking. Its packets has less length when compared to others to make sure that all other nodes hear a collision in progress.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Intersymbol Interference”.

1. What is the full-form of UTP?

a) Unshielded Twisted-Pair copper wire

b) Unshielded Twisted-Pair Coaxial wire

c) Uniquely Twisted-Pair copper wire

d) Uniquely Twisted-Pair Coaxial wire

Answer: a

Explanation: UTP stands for Unshielded Twisted-Pair copper wire. Unshielded in UTP refers to the lack of metallic shielding around copper wires. The twisted pair helps to minimize electronic interference.

2. NIC stands for ________

a) Network Interface Card

b) Network Interface Cable

c) Network Interface Code

d) Network Internal Cord

Answer: a

Explanation: NIC stands for Network Interface Card. It is a computer circuit board that is installed in a computer so that it can be connected to a network.

3. Why CSMA/CD network has a maximum length for cables?

a) to increase the data rate

b) to decrease the data rate

c) to prevent packets from reaching all other nodes

d) to make sure that all other nodes hear a collision in progress

Answer: d

Explanation: CSMA/CD is a media access control used in early Ethernet technology for local area networking. Cables used in CSMA/CD has a maximum length when compared to others to make sure that all other nodes hear a collision in progress.

4. The Clapp oscillator is _________

a) an oscillator made using FET

b) a type of crystal controlled oscillators

c) modified form of Colpitts oscillator

d) modified form of Hartley oscillator

Answer: c

Explanation: Clapp oscillator is just an advanced form of Colpitts oscillator.

5. What is the total voltage, when two noise voltage V 1 and V 2 are combined?

a) \ \

 

 \ V 1 + V 2

Answer: a

Explanation: When two noise voltage V 1 and V 2 are combined, the resulting total voltage V T comes out to be \(\sqrt{V_1 \times V_1 + V_2 \times V_2}\).

6. Shot noise is generated in ________

a) resistors

b) inductors

c) transistors and diodes

d) capacitors

Answer: c

Explanation: Shot noise originate from the discrete nature of electric charge. It is mostly generated in transistors and diodes.

7. Radians per second is equal to _________

a) 2πf

b) phase angle

c) phase deviation

d) phase swing

Answer: a

Explanation: Radians per second is equal to the value 2πf.

8. Repeaters are not required for fiber optic cable lengths upto ________

a) 10km

b) 100km

c) 5km

d) 12km

Answer: b

Explanation: Repeaters are devices which help in retransmitting a signal more powerfully. If the length of fiber optic cable is up to 100 km, there is no need for repeaters in that circuit.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Multiplexing Definition”.

1. A hub _________

a) are more common in token passing circuits

b) cannot be used in an Ethernet type network

c) sends incoming packets out to specific ports like a switch

d) sends incoming packets out to all other terminals connected to it

Answer: d

Explanation: Hubs are devices which are commonly used to connect segments of a LAN. Its role is to send incoming packets out to all other terminals connected to it.

2. A switch _________

a) are more common in token passing circuits

b) cannot be used in an Ethernet type network

c) sends incoming packets out to specific ports

d) sends incoming packets out to all other terminals connected to it like a hub

Answer: c

Explanation: A switch connects different devices together on a computer network by using packet switching to receive, process and forward data to the destination device.

3. What is the advantage of using a switch instead of a hub?

a) it is cheaper when used in large networks

b) it is helpful in placing outputs in an ordered way

c) it reduces the number of collisions

d) it is faster when used in large networks

Answer: c

Explanation: Hubs are devices which are commonly used to connect segments of a LAN. Its role is to send incoming packets out to all other terminals connected to it. But a switch is used frequently instead of a hub to deliver packets to specific ports, Thus, it reduces the chances of collisions.

4. Broadband LANs are provided by cable TV companies for Internet access.

a) True

b) False

Answer: a

Explanation: The term broadband refers to high speed Internet access. It is generally provided by cable TV companies. LAN connects several systems to same network.

5. Why we use record locking in networks?

a) to store records secure

b) to prevent one user from reading a record that another user is writing

c) to prevent multiple users from looking at a document simultaneously

d) to prevent access to any record

Answer: b

Explanation: In networks, record locking is used to prevent the interference of one user in others work, it prevents the user from reading a record that another user is writing.

6. Which software is used to run a client-server network?

a) UNIX

b) Multitasking

c) Windows

d) Microsoft

Answer: b

Explanation: Multitasking is used to run a client-server network.

7. A “thin” client is a ________

a) PC with no disk drives

b) Node that rarely accepts data

c) Node that rarely sends data

d) Node which is active for short period of time

Answer: a

Explanation: A thin client is a dumb terminal. Dumb terminal is simply an output device that accepts data from CPU.

8. IP stands for ________

a) Internet Protocol

b) Internet Process

c) Interconnected Protocol

d) Interconnected People

Answer: a

Explanation: IP stands for Internet Protocol. IP is the principal communication protocol suite for relaying datagrams across network boundaries.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Digital Multiplexing”.

1. If the modulating frequency of a carrier wave varies between 100Hz and 100KHz, find it’s bandwidth?

a) 100 KHz

b) 230.2 KHz

c) 199.8 KHz

d) 123.6 KHz

Answer: c

Explanation: f m = f max – f min = 100KHz – 100Hz = 99.9KHz and Bandwidth = 2f m = 2 x 99.9 = 199.8 KHz.

2. TCP stands for __________

a) Transfer Control Protocol

b) Transmission Control Protocol

c) Transfer Control Process

d) Transmission Control Process

Answer: b

Explanation: TCP stands for Transmission Control Protocol. It is one of the main protocols of the Internet. The entire suite is commonly referred to as TCP/IP. It helps in maintaining network relations which helps in exchanging of data.

3. TCP/IP consists of ________ layers.

a) 5

b) 10

c) 7

d) 18

Answer: a

Explanation: TCP stands for Transmission Control Protocol. It is one of the main protocols of the Internet. It is originated in the initial network implementation in which it complemented the Internet Protocol. The entire suite is commonly referred to as TCP/IP. It consists of 5 layers.

4. What do you understand by IP?

a) Internet Protocol

b) Internet Process

c) Interconnected Protocol

d) Interconnected Process

Answer: d

Explanation: IP stands for Internet Protocol or it can be seen as a connection-less protocol.

5. What is the full form of UDP?

a) User Datagram Protocol

b) User Data Protocol

c) Unique Digital Protocol

d) Unique Data Protocol

Answer: a

Explanation: UDP stands for User Datagram Protocol. It is an alternative for Transmission Control Protocol.

6. What is the lifetime of a packet in an IP network?

a) depends on time elapsed since transmission

b) depends on number of “hops” between nodes

c) approximately 300 milliseconds

d) approximately 500 milliseconds

Answer: b

Explanation: Information is divided into small chunks, called packets. The lifetime of a packet in an IP network depends on the number of “hops” between nodes.

7. The standard Internet address or URL is a 16-bit binary number.

a) True

b) False

Answer: b

Explanation: The standard Internet address or URL is a 32-bit binary number. URL is a web resource that specifies its location on a computer network and a mechanism for retrieving it.

8. DNS stands for __________

a) Domain Name Server

b) Domain Name System

c) Domain Name Society

d) Domain Name Security

Answer: a

Explanation: DNS stands for Domain Name Server. Domain Name Server is a host name to IP address translation service. It is a distributed database implemented in a hierarchy of name servers.

9. Which statement is true about a DNS?

a) has become obsolete on the Internet

b) translates words to numbers

c) stores all domain addresses

d) it has no relation with servers

Answer: b

Explanation: DNS stands for Domain Name Server. Domain Name Server is a host name to IP address translation service. It is a distributed database implemented in a hierarchy of name servers.DNS can translate words to numbers.

10. An intranet connected to the internet is often protected by __________

a) a DNS

b) a “brick wall”

c) a “fire wall”

d) antivirus

Answer: a

Explanation: Intranet uses internet technologies, but is insulated from the global internet. An intranet connected to the internet is often protected by DNS.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Time Division Multiplexing”.

1. The real part of an antenna’s input impedance is due to ________

a) SWR

b) radiated signal

c) reflected signal

d) refracted signal

Answer: b

Explanation: In antenna impedance, impedance related the voltage and current at the input of the antenna. The real part of antenna impedance represents power that is either radiated away or absorbed within the antenna and the imaginary part of antenna impedance represents power that is stored in the near field of antenna.

2. What is the other name for half-wave dipole antenna?

a) Helical antenna

b) Isotropic antenna

c) Hertz antenna

d) Maxwell antenna

Answer: c

Explanation: The Hertz antenna is also known as half wave dipole antenna. It consists of two straight collinear conductors of equal length separated by a small feeding gap.

3. Measured on the ground, the field strength of a horizontally polarized half wave dipole antenna is strongest ________

a) in one direction

b) in two directions

c) depends on the number of elements

d) depends on the shape of antenna

Answer: b

Explanation: As the name suggests, half wave dipole is half wavelength long. This antenna has the shortest resonant length that can be used for a resonant dipole. The field strength of a horizontally polarized half wave dipole antenna is strongest in two directions.

4. When an antenna radiates more energy in one direction than in other directions, it is called ________

a) selectivity

b) directivity

c) active antenna

d) resonance

Answer: b

Explanation: When an antenna radiates more energy in one direction than in other directions is called directivity. An antenna that radiates equally in all directions has effectively zero directionality, and the directivity of this type of antenna should be 1 .

5. What is the full form of ERP?

a) Effective Radiated Power

b) Effective Reflected Power

c) Equivalent Radiated Power

d) Equivalent Reflected Power

Answer: a

Explanation: ERP stands for Effective Radiated Power. Effective Radiated Power  is always given with respect to a certain direction.

6. “Ground Effect” in antenna caused by ________

a) faulty connection of the feed cable ground

b) fading

c) buildings and other structures on ground

d) radio signals reflecting off the ground

Answer: d

Explanation: Radio signals that are reflecting back from the ground is responsible for ground effects in antenna.

7. The polarization of plane waves received from satellite is changed by ________

a) Faraday rotation

b) Gamma rays

c) Helical rotation

d) Distance travelled

Answer: a

Explanation: Generally for satellite communication circular polarization is required. The polarization received by waves from satellite is changed by Faraday rotation.

8. What is the input impedance to a lossless antenna, at resonance?

a) infinite

b) 0

c) resistive

d) capacitive

Answer: c

Explanation: In antenna impedance, impedance related the voltage and current at the input of the antenna. The real part of antenna impedance represents power that is either radiated away or absorbed within the antenna and the imaginary part of antenna impedance represents power that is stored in the near field of antenna. The input impedance of a lossless antenna is purely resistive.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Synchronous TDM”.

1. As the length of a long-wire antenna is increased ________

a) the number of lobes also increase

b) the number of lobes decrease

c) efficiency increase

d) the number of nodes decreases

Answer: a

Explanation: An antenna is basically a transducer that converts radio frequency fields into alternating current or vice versa. They can be used for both transmission and reception of radio signals. If the length of a long wire antenna is increased then the number of lobes also increases. The reception capability of an antenna also depends on it’s length.

2. A non-resonant antenna will ________

a) not transmit

b) not receive

c) cause SWR on the feed cable

d) transmit and receive the signal at the same time

Answer: c

Explanation: A non-resonant antenna have wider bandwidth as compared to the resonant antenna. It also has less sensitivity than resonant antenna. Having less sensitivity means it can amplify weak signals efficiently. A non-resonant antenna will cause SWR on the feed cable.

3. The typical antenna in an AM radio is a ________

a) dipole

b) helical

c) ferrite “loop-stick”

d) loop dipole

Answer: c

Explanation: A ferrite rod antenna is a form of RF design that is universally used in portable transistors broadcast receivers. It is also being used increasingly in wireless applications in areas such as RFID. It is a type of typical antenna in an AM radio. Dipole antenna is the simplest form of antenna. Helical antenna is antenna having quarter wavelength.

4. A 1-MHz monopole antenna must be ________

a) mounted vertically

b) mounted horizontally

c) atleast half lambda wavelength long

d) atleast lambda wavelength long

Answer: a

Explanation: A monopole antenna consists of a straight rod shaped conductor. It is often mounted perpendicularly over some type of conductive surface, called a ground plane.

5. “Ground Effects” in antenna effects ________

a) antenna’s radiation

b) antenna’s gain

c) antenna’s SWR

d) antenna’s power

Answer: a

Explanation: Ground generally reflects the wave back that comes to it. It also affects antenna by effecting the radiation. The radiation intensity of an antenna is determined by comparing it with that of isotropic antenna.

6. An antenna’s beamwidth is measured ________

a) from +90° to -90°

b) between half power points

c) between the minor side lobes

d) between the major side lobes

Answer: b

Explanation: The angle between the half power points of the main lobe with respect to the peak effective radiated power is called half power beamwidth. It is generally measured between half power points.

7. What is the front to back ratio of a half wave dipole antenna?

a) 0 dB

b) 10 dB

c) 100 dB

d) 50 dB

Answer: a

Explanation: The front to back ratio means the ratio of power gain between the front and back of a directional antenna. A half-wave dipolr antenna is one with length half of the wavelength. For a half-wave dipole antenna, its value comes out to be 0dB.

8. AM waves is represented by E t cos⁡ ω c t. What does E t denotes?

a) amplitude of modulated wave

b) amplitude of carrier signal

c) amplitude of modulating signal

d) amplitude of message signal

Answer: a

Explanation: AM wave is represented by Ac(1+x t ) cos⁡ ω c t or E t cos⁡ ω c t, where x t is modulating signal, Ac is amplitude of carrier wave and E t is amplitude of AM wave.

9. The radiation of energy from an antenna can be seen in the ________

a) standing wave around antenna

b) radiation resistance of the antenna

c) reflected resistance of the antenna

d) I2R loss of the antenna

Answer: b

Explanation: An antenna is basically a transducer that converts radio frequency fields into alternating current or vice versa. They can be used for both transmission and reception of radio signals. Radiation resistance of the antenna is just a measure of radiation of energy from antenna.

10. The end-to-end length of a half wave dipole antenna is actually ________

a) slightly shorter than a half wavelength

b) slightly longer than a half wavelength

c) half lambda wavelength

d) lambda wavelength

Answer: a

Explanation: The half wave dipole antenna is also known as Hertz antenna. It consists of two straight collinear conductors of equal length separated by a small feeding gap. The length of half wave dipole antenna is slightly shorter than half wavelength. It’s the simplest form of an antenna.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Asynchronous TDM”.

1. Which is the standard reference antenna for the directive gain?

a) Isotropic antenna

b) Marconi antenna

c) Helical antenna

d) Log Periodic antenna

Answer: a

Explanation: Isotropic antenna is an ideal antenna that radiates its power uniformly in all directions. In practical, no isotropic antenna exists. It is often used as a reference antenna for the antenna gain. Directive gain of a practical antenna is the ratio of the radiation intensity of the antenna to that of an isotropic antenna.

2. Which one of the following reasons for the use of a ground screen with antennas is false?

a) Impossibility of a good ground connection

b) Provision of an earth for the antenna

c) Protection of personnel working underneath

d) Improvement of radiation pattern of antenna

Answer: c

Explanation: If we consider the use of ground as a screen with antenna then there is no chance that it is used for protection of personnel working underneath.

3. Which of the following antennas is best excited from a waveguide?

a) Marconi

b) Horn

c) Helical

d) Discone

Answer: b

Explanation: A horn is an antenna that consists of a flaring metal waveguide that is shaped like a horn. The horn shape helps to direct radio waves in a beam. It is widely used as antennas at UHF.

4. An ungrounded antenna near the ground ________

a) must be horizontally polarized

b) acts as an antenna array

c) is unlikely to need a ground screen

d) acts as a single antenna of twice the height

Answer: b

Explanation: An ungrounded antenna near the ground acts as an antenna array. An antenna array is a combination of multiple antennae which function as a single antenna to perform the required task.

5. Field strength at a distance from an antenna is measured with __________

a) a slotted line

b) a dipole

c) an EIRP meter

d) a field strength meter

Answer: d

Explanation: Field strength meter is an instrument which is used to measure the electric field strength emanating from a transmitter. EIRP  meter is used to measure the radiated power of an antenna in a specific direction.

6. The radiated beam from a parabolic “dish” transmitting antenna is ________

a) dispersed

b) refracted

c) collimated

d) scattered

Answer: c

Explanation: The radiated beam from a parabolic “dish” transmitting antenna is collimated. Collimated light is that light whose rays are parallel due to which it disperse minimally as it propagates.

7. What is the full form of LPDA?

a) Log Periodic Dipole Array

b) Log Periodic Dispersed Array

c) Low Periodic Dispersed Array

d) Low Power Dipole Array

Answer: a

Explanation: LPDA stands for Log Periodic Dipole Array. LPDA consists of a number of half-wave dipole driven elements which gradually increases in length.

8. Arrays in antenna can be __________

a) phased

b) driven

c) parasitic

d) phased, driven or parasitic

Answer: d

Explanation: An antenna array is a group of multiple antenna which behaves as a single antenna to perform the required tasks. Arrays in the antenna can be phased, driven or parasitic.

This set of Basic Analog Communications Questions and Answers focuses on “Practical Aspects of Sampling”.

1. An antenna can be matched to a feed line by using an LC network only.

a) True

b) False

Answer: b

Explanation: An antenna can be matched to a feed line, also known as a transmission line, by using an LC network. But it can also be matched to feed line by a loading coil.

2. An array with one driven element, a reflector, and one or more directors is called ________

a) Yagi

b) Marconi

c) Simple Dipole

d) Folded Dipole

Answer: a

Explanation: A Yagi-Uda antenna is a directional antenna consisting of many parallel elements in a line. It consists of a single driven element which is connected to the transmitter or receiver with a transmission line and also contains parasitic elements which are not connected to the transmitter or receiver. Thus, there are three or four directors and one reflector.

3. The energy picked up by a parabolic antenna is concentrated at the ________

a) edges

b) center

c) corners

d) focus

Answer: d

Explanation: A parabolic antenna is one with parabolic reflector. Energy picked up by a parabolic antenna is concentrated at the focus.

4. Antennas are often tested in ________

a) an RF reflective chamber

b) a vacuum chamber

c) an anechoic chamber

d) atmosphere

Answer: c

Explanation: An antenna is basically a transducer that converts radio frequency fields into alternating current or vice versa. They can be used for both transmission and reception of radio signals. They are often tested in an anechoic chamber. An antenna is used to transmit high frequency waves and plays significant role in the communication process.

5. Which one of the following consists of non-resonant antennas?

a) folded dipole

b) simple dipole

c) rhombic antenna

d) broadside array

Answer: c

Explanation: Non-resonant antennas are like non-resonant transmission lines. Non-resonant transmission lines do not have standing waves. Hence they do not have any reflected wave and they have only forward travelling wave. Whereas resonant antennae have standing wave patterns.

6. Which one of the following is very useful as a multiband HF receiving antenna?

a) folded dipole

b) log periodic

c) conical horn

d) rectangular horn

Answer: b

Explanation: A log periodic antenna is a multi-element, directional, antenna designed to operate over a wide band of frequencies. Whereas, folded dipole and rest work over short band frequencies.

7. Which among the following is not a reason for the use of antenna coupler?

a) To make the antenna look resistive

b) To provide the output amplifier with correct load impedance

c) To discriminate against harmonics

d) To prevent re-radiation of the local oscillator

Answer: d

Explanation: Antenna coupler is a device connected between a radio transmitter or receiver and its antenna to improve power transfer between them. Antenna coupler is never used to prevent re-radiation of the local oscillator.

8. Which of the following term is not applied to the Yagi-Uda array?

a) low impedance

b) high gain

c) good bandwidth

d) high reception of signals

Answer: b

Explanation: A Yagi-Uda antenna is a directional antenna consisting of many parallel elements in a line. It consists of a single driven element and also contains parasitic elements. It consists of 3 or 4 directors and 1 reflector.

9. Why top loading is used with an antenna?

a) to increase its effective height

b) to increase its beamwidth

c) to increase its bandwidth

d) to increase its impedance

Answer: a

Explanation: Length of an and it’s height are significant parameters for the functioning of the antenna. When length of the antenna is shorter than a quarter wavelength ( ʎ ⁄ 4 ), top loading is used to increase its effective height.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Noise in AM”.

1. Why a helical antenna is used for satellite tracking?

a) because of its circular polarization

b) because of its broad bandwidth

c) because of its low bandwidth

d) because of rectangular polarization

Answer: a

Explanation: A helical antenna generally consists of a conducting wire which is wound in the form of a helix. It generally exhibits circular polarization due to which it is mostly used for satellite tracking.

2. Which one of the following noise becomes of great importance at high frequencies?

a) flicker noise

b) shot noise

c) impulse noise

d) transit-time noise

Answer: d

Explanation: If the time taken by electrons to travel from emitter to collector becomes comparable to the period of the signal which is amplified which is only possible at high frequencies called transit time. At transit time noise input admittance of the transmitter increases.

3. Which one of the following statement is false?

a) High Frequency mixers are generally noisier

b) Voltage of impulse noise is independent of bandwidth

c) Thermal noise is not dependent on frequency

d) Flicker noise occurs at low frequency

Answer: b

Explanation: Impulse noise includes unwanted noise which is almost instantaneous and has a sharp sound. High level of such noise may damage internal organs. It depends on bandwidth of the signal.

4. Which of broad classifications of noise are most difficult to treat?

a) noise generated in the receiver

b) noise generated in the transmitter

c) external noise

d) internal noise

Answer: a

Explanation: Noise which is generated inside the receiver is very much difficult to handle.

5. What points must be important to remember, when we deal with random noise calculations?

a) all calculations are based on peak to peak values

b) calculations are based on quantised values

c) calculations are based on average values

d) calculations are based on RMS values

Answer: d

Explanation: All calculations of any random signals are done by using their RMS  values.

6. Which of the following statement is true?

a) Random noise power is inversely proportional to bandwidth

b) Flicker noise occurs at high frequency

c) Noise mixers are caused by inadequate image frequency rejection

d) A random voltage across a resistance cannot be calculated

Answer: c

Explanation: Image frequency rejection is the ratio of intermediate frequency  produced by desired input frequency to that which is produced by the image frequency.

7. Which of the following statement is false?

a) Modulation is used to reduce the bandwidth

b) Modulation is used to separate different transmissions

c) Modulation is used to allow the use of practical antennas

d) Modulation is used to ensure that wave is transmitted over long distances

Answer: a

Explanation: Modulation is the process of varying one or more properties of a periodic waveform that contains the information to be transmitted. It is used to separate different transmission signal so they do not get mixed, it ensure that the wave travels a long distance. But it is not used to reduce bandwidth.

8. Which of the steps is not included in the process of reception?

a) encoding

b) decoding

c) demodulating

d) filtering

Answer: a

Explanation: Communication process is the set of some sequential steps which is involved in transferring messages as well as feedback. The steps included in process of reception are decode – to decode the message signal, interpretation – to interpret the message carefully, and storing – to store the message carefully so that it can use in future if needed.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Noise for DSB-SC”.

1. The discone antenna is ________

a) useful direction-finding antenna

b) used as a radar receiving antenna

c) circularly polarized

d) useful as VHF and UHF receiving antenna

Answer: d

Explanation: A discone antenna is almost same as a biconical antenna in which one of the cones is replaced by a disc. It is mounted vertically, with the disc at top and cone beneath. It is useful as UHF and VHF receiving antenna.

2. Which one of the following is not an omnidirectional antenna?

a) Marconi

b) Discone

c) Log-periodic

d) Half-wave dipole

Answer: c

Explanation: Omnidirectional antenna radiates radio wave power uniformly in all directions in one plane. From above given antennas, log-periodic antenna is not an omnidirectional antenna.

3. If the value of a resistor creating thermal noise is doubled. The noise power generator is therefore ________

a) unchanged

b) doubled

c) quadrupled

d) halved

Answer: a

Explanation: If the value of resistor creating thermal noise is doubled then also the noise power generator remains unaffected, since the two are independent of each other.

4. Which one of the following is not a useful quantity for comparing the noise performance of receivers?

a) Input noise voltage

b) Signal To Noise Ration

c) Noise Figure

d) Figure of merit

Answer: a

Explanation: Noise performance of different receivers cannot be compared on the basis of input noise voltage. It can be calculated on the basis of figure of merit, or noise figure, or on the basis of equivalent noise resistance.

5. Which of the following is the most generally used term for comparing amplifier noise characteristics?

a) signal to noise ratio

b) equivalent noise

c) noise factor

d) figure of merit

Answer: c

Explanation: Noise factor measures degradation of signal to noise ratio which is caused by components in radio frequency  signal chain. It is a number by which the performance of an amplifier can be specified, with lower values indicating better performance.

6. The number of lines per field in the United States TV system is _________

a) 262.5

b) 525

c) 300

d) 600

Answer: a

Explanation: The number of lines per field in the United States TV system is 262.5.

7. The number of frames per second in the United States TV system is _________

a) 262.5

b) 525

c) 45

d) 30

Answer: d

Explanation: The number of frames per second in the United States TV system is 30.

8. Why interlacing is used in television?

a) to reduce noise in video signals

b) to ensure that all the lines on screen are scanned

c) to reduce the disturbances

d) to avoid flicker

Answer: d

Explanation: Interlacing is used for doubling the perceived frame rate of a video display without consuming the extra bandwidth. It is mostly used in television to avoid flicker.

9. The signals sent by the TV transmitters to ensure correct scanning in the receiver are called luminance.

a) True

b) False

Answer: b

Explanation: The signals sent by the TV transmitters to ensure correct scanning in the receiver are called sync. Luminance refers to the component of television which carries information on the brightness of the image. It refers to the intensity of the screen.

This set of Analog Communications online quiz focuses on “Noise for SSB-SC”.

1. The IF bandwidth of a radar receiver is inversely proportional to the __________

a) pulse repetition frequency

b) pulse width

c) pulse amplitude

d) pulse code

Answer: b

Explanation: The IF bandwidth of a radar receiver is inversely proportional to the pulse width.

2. Frequency components of an AM wave are?

a) Carrier frequency (ω c ) with amplitude A

b) Lower side band (ω c + ω m ) having amplitude mA ⁄ 4

c) Upper side band (ω c – ω m ) having amplitude mA ⁄ 4

d) Carrier frequency (ω c ) with amplitude A ⁄ 2

Answer: a

Explanation: Actually the frequency components of AM waves are – Carrier frequency (ω c ) with amplitude A, Lower side band (ω c – ω m ) having amplitude mA ⁄ 2 and Upper side band (ω c + ω m ) having amplitude mA ⁄ 2 .

3. Which of the following statement is true, if a return echo arrives after the allocated pulse interval?

a) it will interfere with the operation of a transmitter

b) the receiver might be overloaded

c) overlap of signals

d) target will appear closer than it really is

Answer: d

Explanation: If a return echo arrives after the allocated pulse interval then the target will always appear closer than it really is.

4. Which of the following statement is true about the spectrum of frequency modulated wave?

a) carrier frequency starts decreasing at a faster rate when the modulation index is large

b) the amplitude of any sideband is totally depends on modulation index

c) total number of sidebands is completely depend on the modulation index

d) carrier frequency is amplified

Answer: b

Explanation: In frequency modulation, frequency of wave is modulated with respect to the wave being propagated. In frequency modulation, the amplitude of any side band depends on modulation index.

5. If a FM signal has modulation index m, then what will be its modulation index after passing through frequency tripler?

a) m ⁄ 3

b) m

c) 3m

d) 9m

Answer: c

Explanation: Frequency multiplier is an electronic circuit that generates an output signal whose output frequency is a multiple of its input frequency. So after passing through frequency tripler, new modulation index will be thrice the input which is 3m.

6. A pre emphasis circuit provides extra noise immunity by __________

a) boosting the base frequencies

b) amplifying the higher audio frequencies

c) amplifying the whole audio band

d) converting the phase modulation to FM

Answer: b

Explanation: Pre emphasis is used to improve the quality of signal at the output of data transmission. A pre emphasis circuit provides extra noise immunity noise amplifying the higher audio frequencies.

7. Which one of the following is not an advantage of FM over AM?

a) Better noise immunity is provided

b) Higher bandwidth is required

c) Transmitting power is useful

d) Less modulating power is required

Answer: b

Explanation: Frequency Modulation has many advantages over amplitude modulation such as it has better noise immune, it requires less modulating power. But it requires higher bandwidth is not an advantage of FM when compared to AM.

8. Which of the following statement about Amplitude Limiter is not true?

a) The circuit is always biased in class C amplifier

b) When the input increases and becomes greater than the threshold of limiting, the gain starts decreasing

c) The output must be tuned

d) Leak-type bias must be used

Answer: a

Explanation: Amplitude Limiter removes the amplitude of output signals to the desired margin irrespective of variations in the input signal. It is always biased in class C amplifier by virtue of the leak-type bias. Amplitude limiter is present in FM receiver and not AM receiver.

9. The typical squelch circuit cuts off __________

a) An audio amplifier when the carrier is absent

b) RF interference when the signal is weak

c) An IF amplifier when Automatic Gain Control is maximum

d) An IF amplifier when Automatic Gain Control is minimum

Answer: a

Explanation: The use of squelch circuit is to suppress the audio or video output of a receiver in the absence of a sufficiently strong desired input signal.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Noise for AM Wave”.

1. The image frequency of a superheterodyne receiver ___________

a) is created within the receiver itself

b) is due to insufficient adjacent channel rejection

c) is not rejected by the IF tuned circuits

d) is independent of the frequency to which the receiver is tuned

Answer: c

Explanation: To eliminate the image frequency of a superheterodyne receiver, adequate attenuation on the incoming signal by the RF amplifier filter is needed. It is not rejected by the IF tuned circuits and thus, it produces image frequency.

2. Which one of the following circuits could not demodulate SSB?

a) Phase Shift Method

b) Filter Method

c) Weaver Demodulator

d) Phase discriminator

Answer: d

Explanation: Phase discriminator cannot be used to demodulate SSB. It is used to discriminate between different phases.

3. Which of the following statement is true about a radio detector?

a) the linearity is worse than in phase discriminator

b) there is stabilization against signal strength variations

c) the final output is twice of that obtainable from a similar phase discriminator

d) the circuit is same as in a discriminator, except that the diodes are reversed.

Answer: a

Explanation: Detector, also known as a demodulator, in a radio receiver extracts the original information that is contained in a modulated radio wave. The linearity of a radio detector is worse than in phase discriminator. However, the radio detector does not get affected by amplitude variations and minimizes the limiting required.

4. To prevent overloading of the IF amplifier in a receiver, one should use _________

a) squelch

b) variable selectivity

c) double conversion

d) variable sensitivity

Answer: a

Explanation: Squelch is a circuit that is preferably used to prevent overloading of the IF amplifier in a receiver.

5. In a broadcast superheterodyne receiver, the ____________

a) Local oscillator always operates below the frequency of transmitted signal

b) Input of mixer must be tuned to the signal frequency

c) Local oscillator frequency should be double than that of IF

d) RF amplifier normally works at 455 KHz above the carrier frequency

Answer: b

Explanation: For a superheterodyne receiver, one of the inputs of the mixer must be tuned to the signal frequency and another input is of the local oscillator frequency. Tuning means that the circuit works for that one signal frequency only.

6. Which of the following statement is false regarding Armstrong modulation system?

a) The system is basically phase modulated and not frequency modulated

b) Automatic Frequency Control  is not needed as a crystal oscillator is used

c) Frequency multiplication must be used

d) Equalization is necessary

Answer: d

Explanation: The Armstrong method generates a double sideband carrier signal, phase shifts this signal and then reinserts the carrier to produce a frequency modulated signal. In Armstrong modulation system equalization is not necessary.

7. If the target cross section is changing, the best system for accurate tracking is __________

a) sequential switching

b) lobe switching

c) conical scanning

d) monopulse radar

Answer: d

Explanation: Monopulse radar compares the received signal from a single radar pulse against itself in order to compare the signal in various aspects. If the target cross section is changing then it is the best system used for accurate tracking.

8. After a target has been acquired, the best scanning system for tracking is _________

a) circular

b) spiral

c) conical

d) helical

Answer: c

Explanation: Conical is the best scanning system for tracking. But it is only preferred for tracking after a target has been acquired.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Noise in FM”.

1. What is the probability density function of thermal noise?

a) Poisson

b) Gaussian

c) Binomial

d) Bessel

Answer: b

Explanation: Thermal noise is approximately white, it means that its power spectral density is nearly equal throughout the frequency spectrum. The amplitude of the signal has a Gaussian probability density function.

2. What is the spectral density of white noise?

a) varies with bandwidth

b) varies with frequency

c) constant

d) infinite

Answer: c

Explanation: White noise consists of signals of all frequencies. Random signals are considered as white noise if they are observed to have a flat spectrum. Its spectral density remains constant.

3. Which is the true statement about noise performance of wideband FM system?

a) it is independent of modulation index

b) more prone to noise interference

c) it is independent of signal to noise ratio

d) it exhibits a threshold

Answer: d

Explanation: Noise performance of wideband FM system exhibits a threshold.

4. What is the power ratio of one decibel?

a) 2:1

b) 1.26:1

c) 3:1

d) 2.5:1

Answer: b

Explanation: Power ratio is a method used by media companies to measure revenue performance compared to the audience share it controls. Power ratio of one decibel is close to 1.26:1.

5. Bit is a unit of ________

a) Channel Capacity

b) Entropy

c) Information

d) Rate of information

Answer: c

Explanation: Bit is a unit of information. Information is the message to be transmitted. It is used in computing and digital communications.

6. What is the maximum possible value of entropy?

a) 1

b) ∞

c) 100

d) 50

Answer: a

Explanation: Entropy is the measure of disorder. Higher the disorder, higher is the entropy of the system. The maximum possible value of entropy is 1.

7. If we double the value of resistor then how it affects the thermal noise power?

a) gets doubled

b) gets halved

c) gets quadrupled

d) remains unchanged

Answer: d

Explanation: The thermal noise power remains unchanged if we double the values of given resistors as both are independent of each other.

8. What is the auto correction function of white noise?

a) Impulse Function

b) Step Function

c) Ramp Function

d) Parabolic Function

Answer: a

Explanation: White noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. Its auto correlation function is an impulse function.

9. Pick the odd one out.

a) Cosmic noise

b) Galactic noise

c) Atmospheric noise

d) Polar noise

Answer: b

Explanation: Galactic noise is a random noise that originates from outside the earth’s atmosphere, whereas others are present in the Earth’s atmosphere.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Threshold Effect in FM”.

1. Which statement is true about thermal noise power?

a) it is proportional to B

b) it is proportional to √B

c) it is proportional to B ⁄ 2

d) it is proportional to √B ⁄ 2

Answer: a

Explanation: Thermal noise is effectively white noise. It extends over a wide range spectrum. Its noise power is proportional to the bandwidth .

2. Cosmic noise is caused by ________

a) Distant stars

b) Lightning discharge

c) Solar eruptions

d) Disturbances in the atmosphere

Answer: a

Explanation: Cosmic noise a random noise that originates from outside the earth’s atmosphere. It can be detected and heard on radio receivers.

3. Which of the following filter is used only at higher frequencies?

a) Ladder

b) Crystal Gate

c) Half Lattice

d) Full Lattice

Answer: a

Explanation: It is the ladder filter which is used only at higher frequencies.

4. Sampling theorem finds application in ________

a) FM

b) PCM

c) AM

d) PM

Answer: b

Explanation: Sampling theorem can be seen as a fundamental bridge between continuous time signals and discrete time signals. It finds its application in Pulse Code Modulation .

5. The channel capacity is exactly equal to which of the following?

a) Bandwidth

b) Noise rate

c) Amount of information per second

d) Entropy

Answer: c

Explanation: The channel capacity of a communication system is exactly equal to the amount of information per second.

6. The ionosphere consists of __________ layer.

a) negative charge

b) positive charge

c) no charge

d) neutral

Answer: a

Explanation: The ionosphere is the ionized part of Earth’s upper atmosphere. It consists of a negative layer.

7. The noise performance of a square law demodulator of AM signal is ___________

a) Identical with that of a synchronous detector

b) Better than that of an envelope detector

c) Better than that of a synchronous detector

d) Poorer than that of an envelope detector

Answer: c

Explanation: The noise performance of a square law demodulator of AM signal is better than that of a synchronous detector.

8. Which system is free from noise?

a) FM

b) AM

c) PCM

d) PM

Answer: a

Explanation: Noise is the unwanted signal or disturbances in a communication system. It is a frequency modulated system which remains free from noise.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Noise in Phase Modulation”.

1. In AM receiver, the oscillator frequency is always ________

a) lower than signal frequency

b) higher than signal frequency

c) equal to signal frequency

d) equal to 1KHz

Answer: b

Explanation: The frequency of an oscillator in amplitude modulated system is always higher than the frequency of signal.

2. Which of the following receiver does not have an amplitude limiter stage?

a) AM

b) PM

c) FM

d) Both AM and FM

Answer: a

Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude present in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency modulation and not in amplitude modulation.

3. Most of the amplification of the received signal is obtained in a superheterodyne receiver from ________ stage.

a) IF

b) RF

c) Power Amplifier

d) Local Oscillator

Answer: a

Explanation: In superheterodyne receiver, most of the received signals gets amplified from an intermediate frequency  due to IF amplifier.

4. Padder capacitor can be used to achieve three point tracking.

a) True

b) False

Answer: a

Explanation: To achieve three point tracking a capacitor is connected in series with local oscillator coil. This capacitor is called a padder capacitor.

5. If the output power of radio receiver is doubled then the volume is increased by _________

a) 3 dB

b) 2 dB

c) -3 dB

d) -2 dB

Answer: a

Explanation: Volume of a radio receiver is increased by 3 dB if we double the output power of a radio receiver.

6. If selectivity is poor then the receiver has poor _________

a) sensitivity

b) diverse reception

c) blocking

d) fidelity

Answer: c

Explanation: By selectivity, receiver responds only to the radio signals, it is tuned to and reject the other signals. If a receiver has poor selectivity then obviously its blocking of unwanted signals is also poor.

7. In FM the carrier deviation is determined by ________

a) Frequency

b) Modulation

c) Amplitude

d) Phase

Answer: b

Explanation: In frequency modulated system, it is the modulation who is responsible for the deviation of the carrier wave.

8. In systems, pre-emphasis is used to amplify ________

a) high frequency

b) low frequency

c) phase

d) amplitude

Answer: a

Explanation: Pre-emphasis is used in frequency modulated or phase modulated transmitters to equalize the drive power of transmitting signal in terms of deviation ratio. It is done at the transmitter. The modulating signal is passed through a simple network at the transmitter which amplifies the high frequency components.

This set of Analog Communications MCQs focuses on “Comparison Between PM and AM”.

1. Which of the following oscillator is not used in frequency modulation?

a) Colpitts Oscillator

b) Crystal Oscillator

c) Hartley Oscillator

d) Both Colpitts and Crystal Oscillator

Answer: b

Explanation: Crystal Oscillator uses the mechanical resonance of a vibrating crystal which is made up of piezoelectric material to create an signal with a precise frequency. It is used to produce a specific fixed frequency. It has no role in frequency modulated systems.

2. In frequency modulation, noise gets decreased if we decrease deviation.

a) True

b) False

Answer: b

Explanation: In frequency modulation, noise is inversely proportional to the frequency deviation. Thus noise also starts decreasing if we increase deviation.

3. Which device is most commonly used for detection in radio receiver?

a) Triode

b) Capacitor

c) Diode

d) Transistor

Answer: c

Explanation: In radio receivers, diode is most preferably used for detection purposes.

4. ________ modulator is an indirect way of generating FM.

a) Varactor FET

b) Reactance FET

c) Armstrong

d) Reactance bipolar transistor

Answer: c

Explanation: FM can be generated in two ways. One is direct and other is indirect way. In indirect way, there is an Armstrong method which is used to generate FM system, while other methods stated in the options are direct ways.

5. Three point tracking is achieved by __________

a) Double conversion

b) Variable selectivity

c) Variable Sensitivity

d) Padder capacitor

Answer: d

Explanation: To achieve three point tracking a capacitor is connected in series with local oscillator coil. This capacitor is called padder capacitor.

6. The household radio receiver uses __________ detector.

a) Synchronous

b) Coherent

c) Radio

d) Envelope

Answer: d

Explanation: Household receivers generally uses envelope detector.

7. High IF in superheterodyne receiver ____________

a) improves fidelity

b) improves selectivity

c) improves sensitivity

d) increases tracking problems

Answer: d

Explanation: In superheterodyne receiver, most of the received signals gets amplified from intermediate frequency . High intermediate frequency helps in tracking problems.

8. If the step size of a system is 0.0721, find its quantization power?

a) 3.25 x 10 -3

b) 4.33 x 10 -4

c) 4.33 x 10 -2

d) 3.25 x 10 -1

Answer: b

Explanation: Quantization noise is a type of quantization error generated by quantization due to analog-to-digital conversion communication systems. It is an approximate error between the analog input voltage to the ADC and the output discritized value.

Therefore, Quantisation power = ∆ 2 /12, where ∆=0.0721

= (0.0721 2 )/12 = 4.33 X 10 -4 .

9. Find the step size of a signal with peak to peak amplitude of 8V and is quantized into 40 levels?

a) 0.8

b) 1

c) 0.2

d) 0.6

Answer: c

Explanation: Step size is the voltage difference between two consecutive digital levels. Quantization step size is the smallest possible difference in amplitude.

Step size, analog-communications-questions-answers-mcqs-q9

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Comparison Between FM and PM”.

1. Pre-emphasis is used to amplify _________ frequencies.

a) low

b) high

c) both low and high

d) local oscillator

Answer: b

Explanation: Pre-emphasis is used in frequency modulated transmitters to equalize the drive power of transmitting signal in terms of deviation ratio. It is done at the transmitter. It is used to amplify high frequencies.

2. De-emphasis circuit is used ________

a) before detection

b) after detection

c) before encoding

d) after encoding

Answer: b

Explanation: De-emphasis means attenuation of those frequencies by the amount by which they are boosted. It is done at the receiver end i.e. it is used after detection.

3. Why frequency fogging is used in a carrier system?

a) to reduce noise

b) to reduce cross talk

c) to converge frequencies

d) to reduce distortion

Answer: b

Explanation: The interchanging of the frequencies of carrier channels to accomplish specific purposes. It is used to prevent feedback and oscillation. It is also used to reduce cross-talk and also to correct for a high frequency response slope in the transmission line.

4. For a phase modulated signal, the frequency deviation is proportional to ________

a) frequency only

b) amplitude only

c) only width

d) phase only

Answer: b

Explanation: For a phase modulated system, it is amplitude which is directly proportional to the deviation.

5. The frequency deviation is proportional to frequency in phase modulated signal.

a) True

b) False

Answer: b

Explanation: In phase modulation, the phase of the carrier signal is varied with respect to the amplitude of the message signal. For a phase modulated signal, the frequency deviation is proportional to amplitude.

6. Which is the true statement about frequency deviation in frequency modulation?

a) frequency deviation is proportional to carrier signal frequency

b) frequency deviation is proportional to amplitude of carrier signal

c) frequency deviation is proportional to modulating frequency

d) frequency deviation is proportional to amplitude of modulating signal

Answer: d

Explanation: In frequency modulated system, the frequency deviation is proportional to the amplitude of the modulating signal.

7. Which of the following is not necessarily an advantage of FM over AM?

a) less modulating power is required

b) better noise immunity is provided

c) higher bandwidth is required

d) carrier is of any shape

Answer: c

Explanation: In frequency modulation, frequency of carrier gets varied with respect to the wave being propagated. FM has many advantages over AM but requirement of higher bandwidth is not an efficient condition.

8. What is number of possible outputs if there is 7 line digital input?

a) 64

b) 32

c) 16

d) 128

Answer: d

Explanation: Total possible outputs will be 2 7 which is equal to 128.

9. What is the frequency of the stereo sub carrier signal in FM broadcasting?

a) 19 KHz

b) 45 KHz

c) 55 KHz

d) 38 KHz

Answer: d

Explanation: Stereo broadcasting is made possible by using a subcarrier on FM radio stations, which takes the left channel and “subtracts” the right channel from it. A subcarrier is basically a sideband of a radio frequency carrier wave, which is modulated to send additional information. The frequency set for stereo sub carrier signal in FM broadcasting is 38 KHz.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Superhetrodyne Receiver”.

1. Which of the following statement is true about frequency modulation?

a) noise gets decrease if we decrease deviation

b) noise gets decrease if we increase deviation

c) noise gets decrease by maintaining deviation constant

d) noise relates parabolically to deviation

Answer: b

Explanation: In frequency modulated system, noise is inversely proportional to the frequency deviation. Thus, if we increase deviation then the noise in system gets decreases.

2. Colpitts oscillator is used in frequency modulation.

a) True

b) False

Answer: b

Explanation: Crystal oscillator is used in frequency modulation to maintain a specific frequency with high stability overall.

3. The difference between phase and frequency modulation ________

a) lies in the poorer radio response of phase modulation index

b) lies in the different definition of modulation index

c) is too great to make the two systems compatible

d) is purely theoretical

Answer: b

Explanation: It is the difference in definition of modulation index and also the general expression of the modulated wave that makes it different between phase and frequency modulated systems.

4. The frequency deviation is proportional to both amplitude and frequency in the phase modulated signal.

a) True

b) False

Answer: b

Explanation: In phase modulation, the phase of the carrier signal is varied with respect to the amplitude of the message signal. For a phase modulated signal, the frequency deviation is proportional to amplitude only.

5. In a frequency modulated signal, the power _________ as the modulation index increases.

a) remains constant

b) increase

c) decrease

d) becomes 0

Answer: a

Explanation: In a frequency modulated system, if we increase the modulation index the power remains constant as the power depends only on the amplitude of the message signal.

6. Frequency fogging is used to reduce noise in a carrier system.

a) True

b) False

Answer: b

Explanation: Frequency fogging is used to cross talk in a carrier system.

7. Pre-emphasis circuit is used ________

a) before detection

b) after detection

c) before encoding

d) after encoding

Answer: c

Explanation: Pre-emphasis is used in frequency modulated or phase modulated transmitters to equalize the drive power of transmitting signal in terms of deviation ratio. It is done at the transmitter. Its circuit is used before modulation.

8. De-emphasis circuit is used in circuit before detection.

a) True

b) False

Answer: b

Explanation: De-emphasis means attenuating those frequencies by the amount by which they are boosted. De-emphasis is done at the receiver end i.e. it is used after detection. Detection refers to demodulation through which the original message signal is retrieved.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “RF Mixing”.

1. For a periodic function, the spectral density and auto-correlation functions are ________

a) Laplace transform pair

b) Fourier transform pair

c) Gauss transform pair

d) Z-transform pair

Answer: b

Explanation: Fourier transform breaks a function into an alternate representation, characterized by sine and cosines. If a function is periodic, the spectral density and auto-correlation functions are Fourier transform pair.

2. Spectral density express ________

a) Average voltage

b) Average power in a waveform as a function of frequency

c) Average noise voltage

d) Average channel capacity

Answer: b

Explanation: Power Spectral Density  of any signal describes the power present in signal as a function of frequency.

3. For a Gaussian process, auto correction also implies _________

a) Statistical dependance

b) Statistical independence

c) Statistical distribution

d) Ergodic process

Answer: b

Explanation: For a Gaussian process, auto correction implies statistical independence. It is basically a stochastic process.

4. What will be the value of modulation if we want maximum undistorted transmitted power?

a) 0

b) 1

c) 0.2

d) 0.5

Answer: b

Explanation: For getting maximum undistorted power in any modulated system, then the modulation index of that system should be 1. Thus, the signal should be 100% modulated.

5. For providing two or more voice circuits on the same carrier, we can use _________

a) SSB

b) ISB systems

c) DSB-SC

d) VSB

Answer: b

Explanation: ISB systems refers to Independent Sideband Mode and is used to provide the same carrier to two or more voice circuits.

6. The output stage of television transmitters is most likely to be a __________

a) Grid modulated class C amplifier

b) Grid modulated class A amplifier

c) Plate modulated class C amplifier

d) Plate modulated class A amplifier

Answer: a

Explanation: The output stage of television transmitters are basically class C amplifiers. It is grid modulated.

7. Modulation is used to separate differing transmission.

a) True

b) False

Answer: a

Explanation: Modulation is the property of varying one or more properties, like amplitude, frequency or phase of a periodic waveform, known as a carrier wave, with respect to the amplitude of the wave to be transmitted. It is used for separating different transmission.

8. A function f is odd, when?

a) f = -f

b) f = f

c) f = -ff

d) f = ff

Answer: a

Explanation: Geometrically a function f is even, if plot of the function is symmetric over y-axis. Algebraically, for any function f to be even, f = f.

While for a function f to be odd, f = -f.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “AM Receiver”.

1. Notch filter is a band pass filter.

a) True

b) False

Answer: b

Explanation: Notch filter is a band stop filter since it allows most frequencies to pass through it, except a specific range. It is also known as band-reject filter. It is just opposite of a band-pass filter.

2. For what modulation index, we can expect maximum undistorted power output of a transmitter?

a) 50%

b) 100%

c) 25%

d) 0

Answer: b

Explanation: For getting maximum undistorted power output, value of modulation index should be 1. If the value of modulation index is 1 then we can say that it is 100% modulated.

3. Modulation is used to allow the use of practical antennas.

a) True

b) False

Answer: a

Explanation: Modulation is the process of varying one or more properties, like amplitude, carrier or phase, of the carrier with respect to the amplitude of the wave being propagated. It is used to separate different transmission signals and also to ensure that a message is transmitted over a long path. It is also used to allow the use of practical antennas.

4. Which of the following statement is incorrect about modulation?

a) It is used to allow the use of practical antennas

b) It is used to separate different transmissions

c) It is used to reduce the required bandwidth

d) It is used to ensure that the message is transmitted over long distances

Answer: c

Explanation: Modulation is the process of varying one or more properties, like amplitude, carrier or phase, of the carrier with respect to the amplitude of the wave being propagated. It is used to separate different transmission signals and also to ensure that the message is transmitted over a long path. It is also used to allow the use of practical antennas.

5. Why amplitude modulation is issued for broadcasting?

a) It is more immune to noise

b) It has more fidelity

c) It avoids receiver complexity

d) It has better selectivity and sensitivity

Answer: c

Explanation: AM broadcasting employs amplitude modulation  transmissions. It is highly used as compared to others for broadcasting purpose since it avoids complexity in receiver.

6. An ergodic process is present in communication if many random signals have ________

a) identical time averages

b) identical ensemble averages

c) identical time and ensemble averages

d) identical bandwidth

Answer: c

Explanation: A stochastic process is said to be ergodic if its properties can be reduced from a single. A non ergodic process changes erratically at an inconsistent rate. Ergodic process exists if many random signals have identical time and ensemble averages.

7. Auto-correlation function is non-unique description of signals.

a) True

b) False

Answer: a

Explanation: Auto-correlation function is also known as serial-correlation. It is the correlation of a function with a delayed copy of itself. So it is non-unique description of signals. It is used for processing signals belonging to series of values.

8. Which of the following statement is not true about auto-correlation function?

a) it is non-unique description of goals

b) it is measure of both time variation and statistical dependence

c) it is an average function

d) it is defined only for periodic signals

Answer: d

Explanation: Auto-correlation function is also known as serial-correlation. It is the correlation of a function with a delayed copy of itself. So it is a non-unique description of signals. It is used for processing signals belonging to a series of values.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “FM Receiver”.

1. What is the auto-correlation function of a signal  at t 0 =0?

a) It is equal to average voltage of the signal

b) It is equal to average power of the signal

c) It is equal to zero

d) It is equal to infinite

Answer: b

Explanation: Auto-correlation function is also known as serial-correlation. It is the correlation of a function with a delayed copy of itself. So it is non-unique description of signals. For a signal  at t 0 =0, it is equal to the average power of the signal.

2. The auto-correlation function is _________

a) impulse function

b) linear function

c) odd function

d) even function

Answer: d

Explanation: Auto-correlation is an even function. Sometimes it is also known as serial-correlation. It is the correlation of a function with a delayed copy of itself.

3. A signal is called ergodic if all type of ensemble averages are constant.

a) True

b) False

Answer: b

Explanation: A random signal is ergodic if time averages equals ensemble averages. Thus, if all type of ensemble averages can be interchanged.

4. A ransom signal is defined as ergodic, if ________

a) all type of ensemble averages are interchangeable

b) all type of ensemble averages are not interchangeable

c) all type of ensemble averages are constant

d) all type of ensemble averages are double than their previous value

Answer: a

Explanation: A stochastic process is said to be ergodic if its properties can be reduced from a single. A non ergodic process changes erratically at an inconsistent rate. Ergodic process exists if many random signals have identical time and ensemble averages. Thus, if all type of ensemble averages can be interchanged.

5. Which statement is correct about ergodic process?

a) ensemble and time averages are different

b) ensemble and time averages are opposite to each other

c) ensemble and time averages are identical

d) ensemble average are exactly twice of time averages

Answer: c

Explanation: A stochastic process is said to be ergodic if its properties can be reduced from a single. A non ergodic process changes erratically at an inconsistent rate. Ergodic process exists if many random signals have identical time and ensemble averages.

6. Communication consists of electrical means of sending information only.

a) True

b) False

Answer: b

Explanation: Communication consists of means of sending, receiving and processing information via electromagnetic waves.

7. In communication system, redundancy ________

a) Helps to detect error

b) Helps to correct error

c) Reduces efficiency of communication

d) Helps to detect and correct error and also reduces efficiency

Answer: d

Explanation: Redundancy helps in many ways in communication. It not only helps to detect an error but also helps in correcting it. It sometimes reduces efficiency also. It is basically the duplication or can say that it is the backup of some important components, so as to efficiently detect the code, with the intention of increasing reliability of the system.

8. Which statement is true about emitter modulator amplifier for amplitude modulation?

a) operates in class A mode

b) operates in class C mode

c) operates in class B mode

d) operates in class D mode

Answer: a

Explanation: Emitter modulator amplifier for AM operates in class A mode and also has very low efficiency. The output of this modulator is very small and therefore it is not suitable for modulation at a high level.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Pre Emphasis and De Emphasis”.

1. Super heterodyne receivers needs an extra circuitry for frequency conversion.

a) True

b) False

Answer: a

Explanation: Super heterodyne receiver mixes the incoming signal frequency with the locally generated signal frequency, using a mixer, in order to convert the incoming RF signal to a low frequency signal which can be processed easily. It has better sensitivity and selectivity but it needs an extra circuitry for frequency conversion.

2. Neper is ________ decibel.

a) smaller than

b) larger than

c) equal to

d) exactly twice of

Answer: b

Explanation: Neper is a unit used to express ratios, such as gain, loss and relative values. One neper is equal to 8.685 dB. Hence it is greater than dB.

3. The coupling used in stoneman transmission bridge is ________

a) Inductive

b) Resistive

c) Capacitive

d) Combination of inductive and capacitive

Answer: c

Explanation: Stoneman transmission bridge is used in telephone communication to separate voice path from signal path and battery. Capacitive coupling is used in it.

4. Which statement is true about Square Law modulators?

a) it is used for frequency modulation

b) it is used for pulse width modulation

c) it is used for amplitude modulation

d) it is used for phase modulation

Answer: c

Explanation: In amplitude modulation, the amplitude of the carrier wave is varied with respect to the instantaneous amplitude of the wave to be transmitted. Square Law modulators are generally used for generation of amplitude modulation. They have nonlinear current-voltage characteristics. They are highly nonlinear in low voltage region.

5. Which statement is true about ring modulator?

a) it is used for DSB-SC generation

b) it is used for SSB-SC generation

c) it is a summation modulator

d) it is used for AM generation

Answer: a

Explanation: Ring Modulator is used for generating DSB-SC waves. It is a product modulator having four diodes connected in the form of a ring, which suppresses the carrier and allows only the two sidebands to be passed.

6. In ergodic process, ensemble and time averages are identical.

a) False

b) True

Answer: b

Explanation: In ergodic process, ensemble and time averages are identical to each other.

7. What is the amount of information in continuous signal?

a) zero

b) infinite

c) 2 bits

d) 4 bits

Answer: b

Explanation: In any continuous signal, the amount of information that comes out is always infinite.

8. Audio frequency range lies between _________

a) 2 MHz to 20 MHz

b) 20 Hz to 20 KHz

c) 20 KHz to 200 KHz

d) 20 MHz to 200 MHz

Answer: b

Explanation: As per standards audio frequency range lies in between 20 Hz to 20 KHz. This is the human audible range.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Heterodyne Receiver”.

1. What is the bandwidth required in SSB signal?

a) f m

b) 2f m

c) > 2f m

d) < 2f m

Answer: a

Explanation: In an AM modulated system, total bandwidth required is from f c + f m to f c – f m i.e. bandwidth is equal to 2f m . In SSB-SC transmission, the carrier and one of the sideband gets suppressed, so the bandwidth becomes f m only.

2. One of the advantage of using a high frequency carrier wave is that it dissipates very small power.

a) True

b) False

Answer: a

Explanation: The main advantage of using high frequency signals is that the signal gets transmitted over very long distances and thus dissipates very less power. The antenna height required for transmission also gets reduced at high frequencies. And also it allows less noise interference and enables multiplexing. This is the reason for sending the audio signals at high frequency carrier signals for communication purpose.

3. What is the function of RF mixer?

a) Addition of two signals

b) Multiplication of two signals

c) Subtraction of two signals

d) To reduce the amount of noise

Answer: b

Explanation: RF mixer translates the frequencies of the two incoming signals by multiplying them and bringing them to a suitable band which can be processed.

4. The antenna current is 10A. Find the percentage of modulation when the antenna current increases to 10.4A?

a) 50%

b) 30%

c) 28.5%

d) 23%

Answer: c

Explanation:

analog-communications-questions-answers-heterodyne-receiver-q4 which gives m = 0.285 or 28.5%.

5. Find the total power, if the carrier of an AM transmitter is 800W and it is modulated to 50%?

a) 100W

b) 800W

c) 500W

d) 900W

Answer: d

Explanation: P T =P C (1+ u 2 ⁄ 2 ), according to the problem P C = 800W and m = 0.5. On substituting values in the equation we get P T =800(1+ 0.5 2 ⁄ 2 ) = 900W.

6. Aliasing refers to ________

a) Sampling of signals less than at Nyquist rate

b) Sampling of signals at Nyquist rate

c) Sampling of signals greater than at Nyquist rate

d) Unsampled the original signal

Answer: a

Explanation: Aliasing refers to the sampling of signals less than at Nyquist rate. Nyquist rate states that the rate of sampling of signals should be greater than or equal to twice the bandwidth of modulating signal. It gets reduced if sampling is done at a higher rate than nyquist rate of sampling. Aliasing can be avoided by using anti-aliasing filters.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “AGC”.

1. Standard intermediate frequency used for AM receiver is ________

a) 455 MHz

b) 455 KHz

c) 455 Hz

d) 20 KHz

Answer: b

Explanation: Standard intermediate frequency  used for AM receiver is 455KHz. IF is obtained by mixing the incoming siganl frequency with the locally generated signal frequency in order to convert the incoming RF signal frequency to a low frequency which can be processed easily.

2. Which device is used in TV receivers for tuning the receiver to the incoming signal?

a) Varacter diode

b) High pass filter

c) Low pass filter

d) Bandpass filter

Answer: a

Explanation: Varacter diodes have variable capacitance as a function of variable input voltage. It works in reverse bias. It is generally used for tuning the receivers according to an incoming signal. It is also used in RF filters for tuning purposes such as tuning of TV sets.

3. What is the bandwidth occupied by a DSB signal when the modulating frequency lies in the range from 100Hz to 10KHz?

a) 19.8 KHz

b) 19.8 Hz

c) 19.8 MHz

d) 19.8 GHz

Answer: a

Explanation: According to given problem, f m = f max -f min = 10KHz – 100Hz = 10000 – 100

= 9900Hz. Therefore bandwidth is equal to 2f m = 2 X 9900 = 19.8 KHz.

4. Which statement is true about multiplexing?

a) it is used to reduce the bandwidth

b) it is used to combine multiple data streams over a single data channel

c) it is used to allow multiple data streams over multiple channels

d) it is used to match and pass the same frequency signal

Answer: b

Explanation: Multiplexing is a process where multiple data streams from different sources are combined and transmitted over a single data channel. It is placed at the transmitting end to combine the signals.

5. What is the noise figure of merit for an SSB modulated signal?

a) less than 1

b) greater than 1

c) 1

d) 0.5

Answer: c

Explanation: Figure of merit is the ratio of output signal to noise ratio to input signal to noise ratio of a receiver system, oftenly used to describe the performance of a system. Figure of merit for SSB modulation is always 1.

6. Which amplifier is preferably used for low level modulation?

a) Class C

b) Class A

c) Class AB

d) Class B

Answer: b

Explanation: We called a modulation as low level when the modulation takes place prior to the output element of the final stage of the amplifier at low power. Class A amplifiers are used for this purpose.

7. If a receiver has a poor capacity of blocking adjacent channel interference then the receiver has ________

a) Poor selectivity

b) Poor Signal to Noise ratio

c) Poor sensitivity

d) Poor fidelity

Answer: a

Explanation: Selectivity is used to separate out closely lying components in terms of frequency. If the receiver has poor selectivity then it also has a poor capacity of blocking adjacent channel interference.

8. What is the advantage of using a VSB transmission?

a) Higher bandwidth than SSB

b) Less power required as compared to DSB-SC

c) Lower bandwidth than SSB

d) Both higher bandwidth than SSB and less power required as compared to DSB-SC

Answer: d

Explanation: Vestigial Side Band is similar to single sideband  transmission, in which the second sideband is not completely removed, but is filtered to remove the range of frequencies that are not required. It has higher bandwidth than SSB-SC and less power consumption than DSB-SC.

9. What is the value of modulation index m, for overmodulation?

a) m < 1

b) m = 1

c) m > 1

d) m = 0

Answer: c

Explanation: When the modulation index m is greater than 1 i.e. m > 1 it is called overmodulation. It generates modulation with distortions and overlapping in the envelope of the modulated signal which makes it difficult to recover the information.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Amplitude Limiting”.

1. TRF receivers are used for ________

a) Detection of modulating signal

b) Removal of unwanted signal

c) Mixing modulating signal with unwanted signal

d) Both detection of modulating signal and removal of unwanted signal

Answer: d

Explanation: TRF receivers are used for detection of modulating signal and removal of unwanted signal. The receiver receive the modulated signal and detect the information signal from received modulating signal.

2. Calculate the power in a DSB-SC signal, if the modulation is 60% and power of carrier wave is 600W?

a) 120W

b) 108W

c) 111W

d) 102W

Answer: b

Explanation: The total power for DSB is P C ( m 2 ⁄ 2 ) = 600X( 0.6 2 ⁄ 2 ) = 108W.

The total power for DSB-SC = P C ( u 2 ⁄ 2 ). (where P c = Power of Carrier, u = Modulation Index) = 600 X  2 /2) = 108W.

3. One of the advantage of using analog communication over digital communication is that in analog communication less transmission bandwidth is required.

a) True

b) False

Answer: a

Explanation: Due to analog to digital conversion, data rate becomes high in digital communication which increases the bandwidth in digital communication. Thus, requirement of bandwidth is more in digital communication than in analog communication.

4. What is the maximum transmission efficiency of an AM signal?

a) 33.33%

b) 60.25%

c) 38.75%

d) 50.25%

Answer: a

Explanation: The percentage of total power contributed by sidebands of the AM signal is known as transmission efficiency of an amplitude modulated system. The maximum transmission efficiency of an AM signal is 33.33%, thus suppressing the carrier which contains no useful information.

5. Generation of SSB-SC signal is done by ________

a) Phase discrimination method and Frequency discrimination method

b) Phase discrimination method and Square law modulator

c) Square law modulator and Frequency discrimination method

d) Balanced modulator and Square law modulator

Answer: a

Explanation: SSB-SC signals are the signals where only one of the side band is transmitted in an AM wave. SSB-SC signal is generated by two methods, frequency discriminator method or filter method and phase discriminator method or phase shift method.

6. In automatic gain control of the AM receiver ________

a) gain of the receiver is adjusted

b) gain adjustment depends upon the strength of received signal

c) is an open-loop system

d) gain is received only by stronger signals

Answer: a

Explanation: Automatic Gain Control provides controlled signal amplitude at the output even if there are amplitude variations at the input. This controlled output adjusts the input to output gain to a suitable value.

7. Which of the following is an example of continuous wave analog modulation?

a) PCM

b) DPCM

c) AM

d) ADM

Answer: c

Explanation: Analog communication is a type in which the message to be transmitted is analog in nature. Here the message signal modulates a high frequency carrier signal. In AM, amplitude of the carrier is varied with respect to the instantaneous amplitude of the wave which is to be propagated. It is also an example of continuous wave analog modulation.

This set of Analog Communications Multiple Choice Questions & Answers  focuses on “Need of Transducers”.

1. What is the effect on the transmitted power, if the modulation index changes from 0.8 to 1?

a) 0.1364

b) 0.239

c) 0.5

d) 0.3333

Answer: a

Explanation: The total power in an AM is given by, P T = P C (1+ m 2 ⁄ 2 ). When modulation index, m = 0.8 P T = P C (1+ 0.8 2 ⁄ 2 )=1.32P c and when modulation index, m = 1 P T =P C (1+ 1 2 ⁄ 2 )=1.5P C .

So increase in power = analog-communications-questions-answers-need-transducers-q1

2. Analog signal may be converted into digital signal by ________

a) Filtering

b) Mixing

c) Sampling

d) Transducing

Answer: c

Explanation: Conversion of an analog signal into digital signal converts a continuous time signal in the form of digits, by discretizing it. Thus, the conversion is done with the help of sampling technique.

3. Radio waves travel through ________

a) Coaxial Cable

b) Wires

c) Optical fiber cable

d) Electromagnetic waves

Answer: d

Explanation: Radio communication or wireless communication takes place through electromagnetic waves. The message is transmitted through open space via electromagnetic waves or radio waves.

4. USB  is the band of frequencies _________

a) below carrier frequency in AM spectrum

b) above the carrier frequency in AM spectrum

c) includes the carrier frequency in AM spectrum

d) is the center frequency

Answer: c

Explanation: Upper Side Band is the band of frequencies above the carrier frequency that lies in AM spectrum. It is a part of the shifted spectrum obtained after amplitude modulation.

5. Which of the following is AM demodulation techniques?

a) Square law demodulator and Envelope detector

b) Ratio detector and PLL detector

c) PLL detector and Coherent detector

d) PLL detector

Answer: a

Explanation: AM signals are detected or demodulated using Square law demodulator and Envelope detector. The demodulator extracts the information from the received AM signal.

6. Vestigial side band signals are detected by ________

a) PLL detector

b) Ratio detector

c) Square law demodulator

d) Synchronous Detection

Answer: d

Explanation: Vestigial side band signals are detected by Synchronous detection or coherent detection technique. The distortion in a VSB signal may be reduced by reducing the modulation index and increasing the width of VSB.

7. What is the function of frequency mixer in super heterodyne receiver?

a) Multiplication of incoming signal and the locally generated carrier

b) Addition of incoming signal and the locally generated carrier

c) Amplification

d) Filtering

Answer: a

Explanation: The function of a frequency mixer in a super heterodyne receiver is that it mixes or multiplies the incoming modulated signal with the locally generated carrier in order to bring the incoming RF signal to a band of frequencies which can be processed easily.

8. The amount of frequency deviation in FM signal depends on ________

a) Modulating frequency

b) Modulation Index

c) Amplitude of the modulating signal

d) Carrier frequency

Answer: c

Explanation: The amount of frequency deviation in the FM signal depends on amplitude of the modulating signal. So for any audio signal, as the loudness increases frequency deviation in carrier signal also increases. Frequency deviation helps in determining the bandwidth of FM signal.