IES - Electrical Engineering - Communication System

IES Electrical Engineering Topic wise QuestionsCommunication System

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YEAR 2008

MCQ 1

Consider the following statements about analog communication and multiplexing :

1. Noise problem for analog communication has the greatest effect on TDM system.

2. Noise problem for analog communication has the least effect on SDM system.

Which of the statements given above is/are correct ?

(A) 1 only

(B) 2 only

(C) Both 1 and 2

(D) Neither 1 nor 2

MCQ 2

Consider the following statements :

1. An active satellite is one carrying a receiver, a transmitter and power supplies.

2. A passive satellite is simply a metallized sphere reflecting radio signals back to the earth.

Which of the statements given above is/are correct ?

(A) 1 only

(B) 2 only

IES EE Topic wise 2001-2008 Communication System

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(C) Both 1 and 2

(D) Neither 1 nor 2

MCQ 3

If the ASCII character H is sent and the character I is received, what type of error is represented ?

(A) Single-bit

(B) Multiple-bit

(C) Burst

(D) Recoverable

MCQ 4

In coding theory, if

L = average word length of the code word

Lmin = minimum average word length of the code word

then what is the efficiency of source-code ( ) ?

(A) LLmin

(B) LLmin

(C) LLmin

(D) LLmin

MCQ 5

With the increase in the transmission bandwidth, received signal-power in AM and FM will, respectively

(A) increase, increase

(B) remain same, increase

(C) increase, remain same

(D) remain same, remain same

MCQ 6

Match List I (Modulation) with List II (Detector/Filter) and select the correct answer using the code given below the lists :


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List I List II

A. PSK 1. Square-law detector

B. FM 2. Ratio detector

C. AM 3. Matched filter

Codes :

A B C

(A) 3 1 2

(B) 3 2 1

(C) 2 1 3

(D) 2 3 1

MCQ 7

Match List I (Characteristic) with List II (Modulation) and select the correct answer using the code given below the lists :

List I List II

A. Capture effect is a characteristic of 1. FDM

B. Granular noise occurs in 2. PCM

C. Guard band is required in 3. FM

Codes :

A B C

(A) 3 2 1

(B) 3 1 2

(C) 1 2 3

(D) 1 3 2

MCQ 8

Which signalling scheme is most affected by noise ?

(A) ASK

(B) FSK

(C) PSK

(D) QAM


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MCQ 9

What are the three steps in generating PCM in the correct sequence ?

(A) Sampling, quantizing and encoding

(B) Encoding, sampling and quantizing

(C) Sampling, encoding and quantizing

(D) Quantizing, sampling and encoding

MCQ 10

In an AM system, for satisfactory operation, carrier frequency must be n times the bandwidth of message-signal. What is the value of n ?

(A) 2>

(B) 5>

(C) 10>

(D) 05>

MCQ 11

For an AM signal, the bandwidth is 10 kHz and the highest frequency component present is 705 kHz. What is the carrier frequency used for this AM signal ?

(A) 695 kHz

(B) 700 kHz

(C) 705 kHz

(D) 710 kHz

MCQ 12

What is the main objective of trellis coding ?

(A) To narrow the bandwidth

(B) To simplify modulation

(C) To increase the data rate

(D) To reduce the error rate

MCQ 13

When zero mean Gaussian noise of variance N is applied to an ideal half-wave rectifier, what is the mean square value of the rectified


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noise ?

(A) /N 4

(B) /N 2

(C) N

(D) N2

MCQ 14

A digital communication system uses 8-PSK modulation and transmits 3600 bps. What is the symbol rate ?

(A) 10800 symbols/sec

(B) 450 symbols/sec

(C) 28800 symbols/sec

(D) 1200 symbols/sec

MCQ 15

If two resistors of values R1 and R2 (at temperatures T1 and T2) are connected in series to form a white noise source, the equivalent noise temperature is

(A) R RR T R T

1 2

1 1 2 2

++

(B) R RR T R T

1 2

1 1 2 2

+

(C) T T1 2+

(D) . .T RR T R

R1

2

12

1

2+

MCQ 16

Assertion (A) : Bandwidth of angle-modulated signal is infinite.

Reason (R) : Angle modulation of a carrier results in the generation of an infinite number of sidebands.

(A) Both A and R are true and R is the correct explanation of A

(B) Both A and R are true but R is not the correct explanation of A

(C) A is true but R is false

(D) A is false but R is true

YEAR 2007


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MCQ 17

Match List I (Mathematical Expression) with List II (Type of Signal) and select the correct answer using the code given below the lists :

[Given ( ), ,m t i 1 2i = : base band message signals; fc : carrier frequency, ( )m tit : Hilbert transform of mi ]

List I List II

A. ( ) ( )cos sinm t t m t ti c c2 + 1. DSB-SC

B. ( ) ( )cos sinm t t m t tc c1 1 + t 2. USB

C. ( ) ( )cos sinm t t m t tc c2 2 t 3. QCM

D ( )cosm t tc1 4. LSB

Codes :

A B C D

(A) 3 4 2 1

(B) 3 4 1 2

(C) 1 2 4 3

(D) 1 2 3 4

MCQ 18

What is the power contained is SSB transmission when the carrier power is 1kW and the modulation index is 0.3 ?

(A) 22.5 W

(B) 90 W

(C) 300 W

(D) 1 kW

MCQ 19

Assertion (A) : Majority of the carrier telephone systems use TDM.

Reason (R) : A TDM system has the capability of achieving a much higher S/N ratio.

(A) Both A and R are true and R is the correct explanation of A

(B) Both A and R are true but R is not the correct explanation of A



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MCQ 20

PLL demodulators are now used in commercial receivers because of which of the following :

1. PLL demodulators do not exhibit threshold in S/N performance

2. No requirement of pre-emphasis and de-emphasis.

3. Cheap PLL ICs are available.

Select the correct answer using the code given below :

(A) 1 and 2

(B) 2 and 3

(C) 1 and 3

(D) 1, 2 and 3

MCQ 21

A carrier is amplitude modulated by 4 signals of frequency 10 kHz, 15 kHz, 20 kHz and 25 kHz. What is the bandwidth of the modulated signal ?

(A) 25 kHz

(B) 50 kHz

(C) 70 kHz

(D) 140 kHz

MCQ 22

What noise is passed through an ideal low-pass filter. Which one of the following is the nature of the auto-correlation function of the filtered output noise ?

(A) Periodic infinite number of zero crossings

(B) Periodic but the number of zero crossings depends on the bandwidth of the filter

(C) Periodic but does not cross zero

(D) A delta function

MCQ 23

Which one of the following is the correct statement ?


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If the channel bandwidth is doubles, the S/N ratio becomes

(A) double of the former S/N ratio

(B) square root of the former S/N ratio

(C) half of the former S/N ratio

(D) none of the above

MCQ 24

Consider a binary linear block code (6, 3) with a generator matrix of the form

G

1 0 0

0 1 0

111

011

0 01 1 01

=

R

T

SSSS

V

X

WWWW

If a code word has been received from the channel as [ ]1 0 1 111 , what is the maximum likelihood decision for the transmitted code word ?

(A) [ ]1 0 1 111

(B) [ ]1 0 0 111

(C) [ ]1 0 1 0 11

(D) [ ]1 0 1 11 0

MCQ 25

If ( )H x is the entropy of a source code, what is the nth order extension of a discrete memory-less source [ ( )]H xn ?

(A) [ ( )]H x n

(B) ( ) logH x n2

(C) ( )n H x

(D) ( )nH x

MCQ 26

For a 10-bit PCM system, the signal to quantization noise ratio is 62 dB. If the number of bits is increased by 2, then how would the signal to quantization noise ratio change ?

(A) Increase by 6 dB

(B) Decrease by 6 dB

(C) Increase by 12 dB

(D) Decrease by 12 dB


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MCQ 27

Voice is digitized using an ADC with a sampling period of 0-1 millisecond and 10 bits/sample. What is the bit rate in kbps generated by this system ?

(A) 100 kbps

(B) 1000 kbps

(C) 9.9 kbps

(D) 10.1 kbps

MCQ 28


An instantaneous code is the one which can be

(A) coded rapidly

(B) coded uniquely

(C) decoded word by word without reference to succeeding code symbols

(D) decoded uniquely

MCQ 29

What is the automatic frequency control voltage of the FM transmitter VCO ?

(A) dc voltage

(B) Since wave voltage

(C) Square wave voltage

(D) Ramp voltage

MCQ 30

A pulse radar is designed to detect objects up to 100 km and the time base is 10 s/km . What is its maximum pulse repetition frequency ?(A) 100 Hz

(B) 1000 Hz

(C) 106 Hz

(D) 109 Hz

MCQ 31


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Time division multiplexing

(A) stacks several channels in adjacent frequency slots

(B) interleaves pulses belonging to different transmissions

(C) combines groups into a single super group

(D) can be used with PCM only

YEAR 2006

MCQ 32

The operating point of RF amplifier in an AM receiver is normally biased in

(A) Class-A

(B) Class-B

(C) Class-C

(D) Class B-C condition

MCQ 33

Which one of the following signals can be applied to a delta modulator whose step size is 0.1 V and sampling frequency is 20 kHz so that no slope overload occurs ?

(A) ( )sin t2 1200

(B) ( )sin t1 2600

(C) 3 (100 )sin t0

(D) ( )sin t4 400

MCQ 34

A sinusoidal signal with a random phase is given by ( ) [ / ( )]sinx t A ft2 2 = + with the probability density function

( )p 1/2 , 0 2

0, otherwise

# # = *

What is the maximum amplitude of the autocorrelation function of this signal ?

(A) A

(B) /A 2


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(C) A2

(D) /A 22

MCQ 35

Which one of the following is the impulse response of a matched filter

for a signal ( )s t of the type shown below ?


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MCQ 36

Which one of the following is the available noise power produced by a noisy resistor R ?

[ Boltzmann Constantk = , ]T BTemperature and Bandwidth= =(A) kTB

(B) kTB4

(C) kTBR4

(D) kTBR2

MCQ 37

A DSB-SC signal is generated using the carrier signal ( )cos tc + and modulating signal ( )m t . What is the envelope detector output of this DSB-SC signal ?

(A) ( )cosm t

(B) ( )m t

(C) ( )tanm t

(D) ( )sinm t

MCQ 38


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Which one of the following sets correctly describes the Block I and Block II in the diagram given below ?

Block I Block II

(A) Integrator Phase modulator

(B) Integrator Frequency modulator

(C) Differentiator Phase modulator

(D) Differentiator Frequency modulator

MCQ 39

The original spectrum of a message contains 100 Hz, 200 Hz frequency components. It is amplitude modulated by a carrier of 0.9 kHz. Which frequency components are contained in the amplitude modulated signal spectrum ?

(A) 900, 1000 and 1100 Hz

(B) 700, 800 and 900 Hz

(C) 700, 800,900, 1000 and 1100 Hz

(D) 100, 200 and 900 Hz

MCQ 40

If two signals modulate the same carrier with different modulation depths of 0.3 and 0.9, the resulting modulation signal will

(A) be over-modulated

(B) have the resultant modulation limited to 1.0

(C) have the resultant modulation index around 0.82

(D) have the resultant modulation index around 0.95

MCQ 41


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Match List I (Modulation) with List II (Application) and select the correct answer using the code given below the lists :

List I List II

A. Wide band FM 1. Mobile communication

B. Narrow band FM 2. Superimposition of binary waveform on carrier

C. AM 3. TV video

D VSB-AM 4. TV audio

5. Medium wave broadcast

Codes :

A B C D

(A) 4 3 5 1

(B) 5 1 2 3

(C) 4 1 5 3

(D) 5 3 2 1

MCQ 42

Match List I (Parameter) with List II (Value of Parameter) and select the correct answer using the code given below the lists :

List I List II

A. Line blanking period 1. 4.5 to 4.9 s

B. Line synchronization pulse 2. 155 to 165 s

C. Vertical field period 3. 11.8 to 12.3 s

D During of pre-equalizing pulse sequence 4. 20,000 s

Codes :

A B C D

(A) 3 1 4 2

(B) 4 2 3 1

(C) 3 4 1 2

(D) 4 3 2 1


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MCQ 43

Which of the following are the advantage of FM broadcasting over AM broadcasting

1. Better S/N ratio

2. Not subject to signal fading

3. Power efficiency is superior

4. Demodulation is simpler

Select the correct answer from the code given below

(A) 1 and 2

(B) 1, 2 and 4

(C) 2, 3 and 4

(D) 1 and 3

MCQ 44

Consider the following statements about analog data-digital signal :

1. Amplifiers used in repeaters produce additive noise

2. FDM is used for digital signals whereas TDM is used for analog signals

3. With TDM there is no intermodulation noise whereas this is a concern for EDM

4. Conversion to digital signalling allows the use of efficient digital switching techniques

Which of the statements given above are correct ?

(A) 1 and 2

(B) 3 and 4

(C) 1, 2 and 3

(D) 1, 2 3 and 4

Direction : The following four items consist of two statements, one labelled as Assertion A and the other labelled as Reason R. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below.

Codes :(A) Both A and R are true and R is the correct explanation of A


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(B) Both A and R are true but R is the NOT the correct explanation of A



MCQ 45

Assertion (A) : In frequency division multiplexing (FDM), different carriers are to be generated for different channels. Also, each channel occupies a separate frequency band and different band pass filters are employed.

Reason (R) : The non-linearities in various amplifiers of an FDM system do not produce any harmonic distortion and three is no interference within the channels.

YEAR 2005

MCQ 46

An AM voltage signal ( )s t , with a carrier frequency of 1.15 GHz has a complex envelope ( ) [1 ( )], 500g t A m t A Vc c= + = , and the modulation is a 1 kHz sinusoidal test tone described by ( ) . ( )sinm t t0 8 2 103#=, appears across a 50 resistive load. What is the actual power dissipated in the load ?

(A) 165 kW

(B) 82.5 kW

(C) 3.3 kW

(D) 6.6 kW

MCQ 47

A broadcast AM radio transmitter radiates 125 kW when the modulation percentage is 70. How much of this is carrier power ?

(A) 25. kW

(B) 50. kW

(C) 75. kW

(D) 100. kW

MCQ 48


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When a radio receiver is tuned to 555 kHz, its local oscillator provides the mixer with an input at 1010 kHz. At the output, another signal is also received along with the desired signal. What is the frequency of the other station ?

What is the frequency of the other station ?

(A) 910 kHz

(B) 355 kHz

(C) 455 kHz

(D) 1465 kHz

MCQ 49

Which of the following is not a component of PLL ?

(A) Frequency multiplier

(B) Phase detector

(C) VCO

(D) Loop filter

MCQ 50

Which of the following modulated signals can be detected by an envelope detector ?

(A) DSB-suppressed carrier

(B) DSB-full carrier

(C) Frequency modulated signal

(D) SSB-suppressed carrier

MCQ 51

A given AM broadcast station transmits an average carrier power output of 40 kW and uses a modulation index of 0.707 for sine wave modulation. What is the maximum (peak) amplitude of the output if the antenna is represented by a 50 resistive load ?

(A) 50 kV

(B) 50 V

(C) 3.414 kV

(D) 28.28 kV


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MCQ 52

A microphone with inbuilt amplifier has an output noise level in a very quiet room of about 30 V rms. The maximum output level is about 300 mV rms before severe distortion occurs. What dynamic range does this represent in dB ?

(A) 4 dB

(B) 36 dB

(C) 40 dB

(D) 80 dB

MCQ 53

Which one of the following statements is correct ?

Noise has the greatest effect in a communication system when it interferes with the signal

(A) in the transmitter

(B) in the channel

(C) in the receiver

(D) in the transducer

MCQ 54

Match List I (Signal) with List II (Spectrum) and select the correct answer using the code given below the lists :


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Codes :

A B C D

(A) 1 3 2 4

(B) 2 4 1 3

(C) 2 3 1 4

(D) 1 4 2 3

MCQ 55

Analog data having highest harmonic at 30 kHz generated by a sensor has been digitized using 6-level PCM. What will be the rate of digital signal generated ?

(A) 120 kbps

(B) 200 kbps

(C) 240 kbps

(D) 180 kbps


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MCQ 56

The channel capacity of a noiseless channel is equal to

(A) Rate at which information is transmitted

(B) Signalling speed

(C) Bandwidth

(D) Bandwidth-SNR product

MCQ 57

Match List I (Coding Technique in Digital Communication systems) with List II (Purpose) and select the correct answer using the code given below the lists :

List I List II

A. Huffman code 1. Elimination of redundancy

B. Error correcting code 2. Reduces bit rate

C. NRZ-coding 3. Adapts the transmitted signal to the line

D Delta modulation 4. Channel coding

Codes :

A B C D

(A) 1 2 3 4

(B) 3 4 1 2

(C) 1 4 3 2

(D) 3 2 1 4

MCQ 58

To overcome slope overload problem, which type of the integrator is used in delta modulation ?

(A) Fixed slope integrator

(B) Variable slope integrator

(C) Linear slope integrator

(D) Bipolar integrator

MCQ 59


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Quantization noise occurs in

(A) Pulse amplitude modulation

(B) Pulse width modulation

(C) Pulse code modulation

(D) Pulse position modulation

Direction : The following item consist of two statements, one labelled as Assertion A and the other labelled as Reason R. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below.


(B) Both A and R are true but R is NOT the correct explanation of A



MCQ 60

Assertion (A) : Vestigial Side Band (VSB) modulation is used for TV broadcasting.

Reason (R) : Video signals have negligible power at low frequencies.

YEAR 2004

MCQ 61

Which one of the following statements is correct ? In PCM, the conditional probability of error is proportional to

(A) noise power ( )N0

(B) Peak signal energy ( )Emax

(C) N0

(D) Emax

MCQ 62

Which one of the following statements is correct ? In TDM, non-


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essential frequency components of the modulating signal are removed by

(A) sampler

(B) attenuator

(C) pre-alias filter

(D) modulator

MCQ 63

Which one of the following statements is correct ? For coherent detection of digital signals, the receiver must be

(A) synchronized in time only

(B) synchronized in phase only

(C) unsynchronized in time and phase

(D) unsynchronized

MCQ 64

For a binary symmetric channel, which one of the following is the correct expression for entropy ? (p =conditional probability of error).(A) ( / ) ( ) { /( )}log logp p p p1 1 1 12 2+

(B) {1/(1 )} (1 ) (1/ )}log logp p p p2 2 +

(C) ( / ) { /( )}log logp p2 1 2 1 12 2+

(D) ( ){ ( / )} { /( )}log logp p p1 1 1 12 2 +

MCQ 65

In amplitude modulation, the modulation envelope has a peak value which is double the unmodulated carrier value. What is the value of the modulation index ?

(A) 25 %

(B) 50 %

(C) 75 %

(D) 100 %

MCQ 66

Si and So denote the signal at input and output of a linear network Ni and No are the corresponding noises. Which one of the following


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is the correct expression for noise figure of the network ?

(A) N NS Si o

i o

(B) S NS No o

i i

(C) S NS No i

i o

(D) S NS Ni i

o o

MCQ 67


One hundred percent modulation of the carrier for the broadcast FM radio band is achieved when

(A) carrier frequency changes by %100!

(B) carrier envelope changes by %100!

(C) carrier frequency changes by 75 kHz!

(D) audio frequency changes by 15 kHz!

MCQ 68

In case of data transmission, which one of the following systems will give the maximum probability of error ?

(A) ASK

(B) FSK

(C) PSK

(D) DPSK

MCQ 69


The type of modulation used generally in TV transmission for video and audio signals, respectively, are

(A) FM and AM

(B) FM and FM

(C) AM and AM

(D) AM and FM


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MCQ 70

Match List I (FM Service Type) with List II (Channel Bandwidth) and select the correct answer using the codes given below :

List I List II

A. Commercial FM radio broadcast 1. 100 kHz

B. Television sound 2. 15 kHz

C. Police, fire, ambulance etc 3. 200 kHz

D Amateur radio 4. 20 kHz

Codes :

A B C D

(A) 4 2 3 1

(B) 4 1 3 2

(C) 3 1 4 2

(D) 3 2 4 1

MCQ 71

Which one of the following statements is correct ? The capacitor charging time in the AM envelope demodulator is based on the time for one

(A) half cycle of the carrier frequency

(B) quarter cycle of the carrier frequency

(C) half cycle of the lowest audio frequency

(D) quarter cycle of the highest audio frequency

MCQ 72


Quantising noise is produced in

(A) all pulse modulation systems

(B) PCM

(C) all modulation systems

(D) FDM


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MCQ 73


The equalizing pulses in television transmission are sent during

(A) vertical blanking

(B) horizontal blanking

(C) horizontal retrace

(D) picture forward trace

MCQ 74

Which one of the following represents the Fourier Transform ( )X j of the signal ( ) ( )x t te u tat= ?

(A) ( )( )

X ja jj = +

(B) ( )( )

X ja jj

2 =+

(C) ( )( )

X j ja j 2

= +

(D) ( )( )

X ja j

12

=+

YEAR 2003

MCQ 75

For an AM signal, the bandwidth is 10 kHz and the highest frequency component present is 705 kHz. The carrier frequency used for this AM signal is

(A) 695 kHz

(B) 700 kHz

(C) 705 kHz

(D) 710 kHz

MCQ 76

If large amount of information is to be transmitted in a small amount of time, we require

(A) Low-frequency signals

(B) Narrow-band signals


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(C) Wide-band signals

(D) High-frequency signals

MCQ 77

Match List I (System) with List II (Application) and select the correct answer :

List I List II

A. Pre-emphasis 1. AM Detector

B. Armstrong Method 2. FM Receiver

C. Envelope Detector 3. FM Generator

D De-Emphasis 4. FM Transmitter

5. AM Transmitter

Codes :

A B C D

(A) 4 3 2 1

(B) 3 5 1 2

(C) 4 3 1 2

(D) 5 3 2 1

MCQ 78

A modulator is a device to

(A) Separate two frequencies

(B) Impress the information on to a radio frequency carrier

(C) Extract information from the carrier

(D) Amplify the audio frequency signal

MCQ 79

A modulation technique in which bandwidth of the modulated signal is extended well beyond the bandwidth of the modulating signal, independent of the modulating signal bandwidth, is called

(A) Wide-band modulation

(B) Extended bandwidth modulation


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(C) Spread spectrum modulation

(D) Narrow-band modulation

MCQ 80

In AM, the percentage of total power in sideband is

(A) 10 %

(B) 16.67 %

(C) 23.34 %

(D) 37.5 %

MCQ 81

Which of the following desirable features are possessed by SSB in comparison to AM ?

1. Less power is required

2. Bandwidth required is less

3. Antenna size can be reduced

4. Lower frequency can be used

Select the correct answer using the codes given below :

(A) 3 and 4

(B) 2, 3 and 4

(C) 1 and 2

(D) 1, 2 and 4

MCQ 82

The detection-gain for coherent DSB demodulator is

(A) 2

(B) 4

(C) 8

(D) 16

MCQ 83

Power spectral density of a signal is

(A) Complex, even and nonnegative

(B) Real, even and nonnegative


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(C) Real, even and negative

(D) Complex, odd and negative

MCQ 84

Which one of the following multiplexing techniques involves signals composed of light beams ?

(A) CDM

(B) FDM

(C) TDM

(D) WDM

MCQ 85

In a communication system, a process for which statistical averages and time-averages are equal, is called

(A) Stationary

(B) Ergodic

(C) Gaussian

(D) BIBO stable

MCQ 86

In which type of the switching given below, entire capacity of a dedicated link is used ?

(A) Circuit switching

(B) Data gram packet switching

(C) Virtual circuit packed switching

(D) Message switching

MCQ 87

In TV transmission, the modulation schemes for Video and Audio are, respectively

(A) FM and AM

(B) FM and FM

(C) AM and FM

(D) AM and AM


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Direction : The following two items consist of two statements, one labelled as Assertion A and the other labelled as Reason R. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below.

Codes :(A) Both A and R are true R is the correct explanation of A




MCQ 88

Assertion (A) : Microwave links are generally preferred to coaxial cable for TV transmission.

Reason (R) : Microwave links have greater bandwidth than coaxial cables.

MCQ 89

Assertion (A) : FM transmission is noise free.

Reason (R) : In FM, information is carried as frequency variation.

YEAR 2002

MCQ 90

Let ( )x t be a real signal with the Fourier transform ( )X f . Let ( )X f) denote the complex conjugate of ( )X f . Then

(A) ( ) ( )X f X f = )

(B) ( ) ( )X f X f =

(C) ( ) ( )X f X f =

(D) ( ) ( )X f X f = )

MCQ 91

Let the transfer function of a network be ( ) ( )H f H f e e2( )j f j f4= = .


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If a signal ( )x t is applied to such a network, the output ( )y t is given by

(A) ( )x t2

(B) ( )x t 2

(C) ( )x t2 2

(D) 2 ( 4 )x t

MCQ 92

The maximum number of quantized amplitude levels, in a 3-digit ternary PCM system can be used to represent is

(A) 8

(B) 9

(C) 27

(D) 81

MCQ 93

The waveform ( )cos cosA t k t1 2 + is(A) amplitude modulated

(B) frequency modulated

(C) phase modulated

(D) frequency as well as phase modulated

MCQ 94

Let ( ) ( )cos sinx t t t5 50 5= + . Its instantaneous frequency (in rad/s) at t 0= has the value(A) 5

(B) 50

(C) 55

(D) 250

MCQ 95

The performance of the DPCM-Coder improves as the

(A) input probability density becomes more and more Gaussian

(B) input power spectral density tends to be white

(C) input dynamic range increases


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(D) sample-to-sample correlation of the input increases

MCQ 96

An FM wave uses a 2-5 V, 500 Hz modulating frequency and has a modulation index of 50. The deviation is

(A) 500 Hz

(B) 100 Hz

(C) 1250 Hz

(D) 2500 Hz

MCQ 97

Match List I (Modulation/reception techniques) with List II (Disadvantages) and select the correct answer :

List I List II

A. Superheterodyne receiver 1. Threshold effect

B. FM 2. Granular noise

C. PCM 3. Image frequency interference

D Delta modulation 4. Quantization noise

Codes :

A B C D

(A) 1 3 4 2

(B) 3 1 4 2

(C) 1 3 2 4

(D) 3 1 2 4

MCQ 98

Consider a binary Hamming code of block length 31 and rate equal to (26/31). Its minimum distance is

(A) 3

(B) 5

(C) 26

(D) 31


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MCQ 99

A satellite channel can be fairly accurately modelled as a

(A) random delay channel

(B) panic button channel

(C) additive white Gaussian noise channel

(D) fading channel

MCQ 100

One disadvantage of adaptive delta modulation over linear delta modulation is that it

(A) requires more bandwidth

(B) is more vulnerable to channel errors

(C) requires a large number of comparators in the encoder

(D) is not suitable for signals with periodic components

MCQ 101

An MTI radar is operating at the wavelength of 5 10 2# m and the pulse repetition frequency (PRF) is 1000. Then the first blind speed (in m/s) occurs at

(A) 25

(B) 50

(C) 500

(D) 1000

MCQ 102

Consider the following statements :

If the maximum range of a radar has to be 4 times,

1. the peak transmitted power may be increased 16 fold

2. the antenna diameter may be doubled

3. the sensitivity of the receiver may be doubled

4. the transmitted pulse width may be doubled

Which of these statements are correct ?

(A) 1 and 2

(B) 2 and 3


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(C) 3 and 4

(D) 1 and 4

MCQ 103

With reference to a pulsed radar, match List I (Problem) with List II (Causes) and select the correct answer :

List I List II

A. Second time around echo 1. Broad transmitted pulse

B. Blind speeds 2. Inadequate detection threshold

C. Inadequate range resolution 3. MTI filter

D False alarms 4. Inadequate Inter Pulse Period

Codes :

A B C D

(A) 4 3 1 2

(B) 1 2 4 3

(C) 4 2 1 3

(D) 1 3 4 2

MCQ 104

Assertion (A) : Slope overload is a problem in D.P.C.M.

Reason (R) : D.P.C.M. makes use of adjacent sample correlations.

MCQ 105

Assertion (A) : Thermal noise in metallic resistors can be characterized by Gaussian probability density function.

Reason (R) : Power spectral density of thermal noise is essentially constant for a very large frequency range.

YEAR 2001

Direction : The following two items consist of two statements, one labelled as Assertion A and the other labelled as Reason R. You are to examine these two statements carefully and decide if the Assertion


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A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below.





MCQ 106

Assertion (A) : Linear AM detector applied with two amplitude-modulated waves simultaneously, one being very weak with respect to the other, detects only the strong signal.

Reason (R) : Detector selectively is increased in the presence of strong signal.

MCQ 107

Assertion (A) : Coherent FSK system is preferred over non-coherent FSK.

Reason (R) : Coherent FSK requires less power than non-coherent FSK.

MCQ 108Slope overload occurs in delta modulation when the

(A) frequency of the clock pulses is too low

(B) rate of change of analog waveform is too large

(C) step size is too small

(D) analog signal varies very slowly with time

MCQ 109

In an AM signal when the modulation index is one, the maximum power Pt , (where Pc is the carrier power) is equal to

(A) Pc

(B) . P1 5 c


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(C) P2 c

(D) . P2 5 c

MCQ 110

In the frequency modulation if fm is modulating frequency, f is maximum frequency deviation and B is bandwidth, then

(A) B f fm= +

(B) B f fm=

(C) ( )B f f2 m= +

(D) ( )B f f2 m=

MCQ 111

A DSB suppressed carrier reception is shown in the above figure. If (SNR)i is the S/N ratio for direct (incoherent) detection and ( )SNR s is that for coherent synchronous detection, then

(A) ( ) 2 )SNR (SNRs i=

(B) ( ) ( )SNR SNRs i=

(C) ( ) ( )4SNR SNRs i=

(D) ( ) / ( )1 2SNR SNRs i=

MCQ 112

An AM superheterodyne receiver with IF of 455 kHz is tuned to the carrier frequency of 1000 kHz. The image frequency is

(A) 545 kHz

(B) 1 MHz

(C) 1455 kHz

(D) 1910 kHz

MCQ 113

A 4 GHz carrier is amplitude-modulated by a low-pass signal of


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maximum cut off frequency 1 MHz. If this signal is to be ideally sampled, the minimum sampling frequency should be nearly

(A) 4 MHz

(B) 4 GHz

(C) 8 MHz

(D) 8 GHz

MCQ 114

If the modulation index of an AM wave is changed from 0 to 1, the transmitted power

(A) increases by 50 %

(B) increases by 75 %

(C) increases by 100 %

(D) remains unaffected

MCQ 115

Which one of the following PCM schemes is depicted in the above figure ?

(A) Adaptive DM

(B) Differential PCM

(C) Companding

(D) Delta Modulation

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IES - Electrical Engineering - Communication System

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