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Test: Communication System - Electronics and Communication Engineering (ECE) MCQ


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26 Questions MCQ Test GATE ECE (Electronics) Mock Test Series 2025 - Test: Communication System

Test: Communication System for Electronics and Communication Engineering (ECE) 2024 is part of GATE ECE (Electronics) Mock Test Series 2025 preparation. The Test: Communication System questions and answers have been prepared according to the Electronics and Communication Engineering (ECE) exam syllabus.The Test: Communication System MCQs are made for Electronics and Communication Engineering (ECE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Communication System below.
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Test: Communication System - Question 1

The DSB-SC signal recevied at the output of a channel is given as S(t) = 2 cos2π(103 - 0.5). cos2π(106 -
1). Determine the group delay  and phase delay  introduced by the channel.

Detailed Solution for Test: Communication System - Question 1

For an amplitude modulated signal
the delay in carrier frequency
component gives phase delay and
delay in baseband (message)
signal gives the group delay.
{Reference: Page No 98, Simon
Haykin, common system 3rd
edition}

Test: Communication System - Question 2

Which of the following is incorrect about hilbert-transform?

Detailed Solution for Test: Communication System - Question 2

xh (t) is delayed version by -900 of
x(t)

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Test: Communication System - Question 3

An amplitude modulated signal is given as s(t) = 14 cos8000πt + 20 cos10000πt + 14 cos12000πt.
Determine the modulation depth.

Detailed Solution for Test: Communication System - Question 3

Test: Communication System - Question 4

An amplitude modulated signal is given as S(t) = 10 (2 + cos2π x 104t) cos2π x 107t. If the carrier
frequency component is suppresed before transmission, then determine the percentage power
saved.

Detailed Solution for Test: Communication System - Question 4

Test: Communication System - Question 5

Suppose that non linear device (NLD) is available for which the output voltage V0 and input voltage Vi are related by V0(t) = a1   where a1 and a3 are constants. Let Vi = m (t) + cos2πfct and a1 = 1, a2 = 1. To generate a DSB-SC signal having carrier frequency is 5MHz, this NLD is followed by a BPF of appropriate centre frequency and band width. Determine fc

Detailed Solution for Test: Communication System - Question 5

Test: Communication System - Question 6

Consider a square law device having input voltage Vi and output voltage V0 are related as

This SLD is used to generate an standard AM with a carrier frequency of 3MHz, as shown in the circuit below.

Determine the maximum bandwidth of message signal m(t) so that spectrum of s(t) is nonoverlapping.

Detailed Solution for Test: Communication System - Question 6

i.e the maximum bandwidth of
message signal may be 1MHz

 

Test: Communication System - Question 7

A message signal m(t) = 4 cos2πx 104 t is used to generate an FM signal. Determine the minimum
value of (Δf)max so that modulation efficiency is 100%.

Detailed Solution for Test: Communication System - Question 7

M(t) = 4cos2π x 104t
Here Am = 4, fm = 10 KHz,
Modulation efficiency is 100%

when βf = 2.4, 5.5, 8.6-----

Test: Communication System - Question 8

A phase-modulated signal is given as S(t) = 30 cos[2πx108t + 100 cos2πx104t]. Determine the
transmission bandwidth required according to carson’s approximation.

Detailed Solution for Test: Communication System - Question 8

= 2 (100 + 1) x 10
= 20 x 101
= 2020 KHz
= 2.02 MHz

Test: Communication System - Question 9

Consider an FM signal, S(t) = 10 cos[2π x107t + 10 sin2π x103t]. Determine Kp/Kf if the above modulated signal is assumed phase-modulated signal.

Detailed Solution for Test: Communication System - Question 9

Test: Communication System - Question 10

The following message signal m(t) is given to both frequency modulator and phase modulator. If
the maximum phase deviation of both FM and PM is same, determine the Kf/Kp.

Detailed Solution for Test: Communication System - Question 10

and maximum phase-deviation of
FM signal

 

Test: Communication System - Question 11

Consider a sine wave of frequency 2 KHz and peak amplitude AM. This signal is applied to a delta modulator of step-size 0.4 Volt and sampling period 3.18 x 10-6 sec. What is the maximum power that
may be transmitted without slopeoverload distortion?

Detailed Solution for Test: Communication System - Question 11

Test: Communication System - Question 12

A PCM system uses an uniform quantizer followed by a 7-bit binary encoder. The bit rate of the system is equal to 50x106 bits/ second. Determine the output signal to quantization noise ratio when a full-load sinusoidal modulating signal of frequency 1MHz is applied to the input.

Detailed Solution for Test: Communication System - Question 12

(SNR) = (6n + 1.8) dB
= 6 x 7 + 1.8
= 43.5 dB

Test: Communication System - Question 13

An analog signal is sampled, quantized and encoded into a binary PCM system. The specifications of the PCM system include the following: Sampling role = 8 KHz Number of representation levels = 64
Determine the minimum bandwidth required if PCM wave is transmitted over a baseband channel.

Detailed Solution for Test: Communication System - Question 13

Test: Communication System - Question 14

A binary PCM system uses pulse P(t) to transmit symbol 1 and - P(t) to transmit symbol 0. The additive noise at the reciever input is white and Gaussian, with zero mean and power spectral density
10-10 W/Hz. Assuming that symbols 1 and 0 occur with equal probability, determine the probability of error at the reciever output.

Detailed Solution for Test: Communication System - Question 14

For binary polar signal the
probability of error is given as

Test: Communication System - Question 15

A source emits one of four symbols S0, S1, S2 and S3 with probabilities 1/3, 1/6, 1/4 and 1/4 respectively.
The successive symbols emitted by the source are statistically independent. Calculate the entropy
of the source.

Detailed Solution for Test: Communication System - Question 15

Test: Communication System - Question 16

Consider a sinusoidal signal with random phase, defined by X(t) =  where A and fare constants and θ is a random variable that is uniformly distributed over the interval  Determine the autocorelation function of X (t)

Detailed Solution for Test: Communication System - Question 16

The probability function of random
variable is given as,

Now the auto-corelation function
of X(t)

Test: Communication System - Question 17

Probability density function of a random variable X is given below

P (X ≤ 4) is

Detailed Solution for Test: Communication System - Question 17

Test: Communication System - Question 18

A 1W video signal having bandwidth of 200 MHz is transmitted to a reciver through a cable that has 50 dB loss. If the efficitive two sided noise power spectred density at the receiver is 10-20 Watt/Hz, then the signal to noise ratio at the receiver is

Detailed Solution for Test: Communication System - Question 18

PS = 1 W
Since cable loss is 50 dB (105), So
power at the input of reciever
PS = 10-5 Watts
Noise power = 2 x200 x106 x10-20
2, Because of two sided PSD
= 4 x 10-12 Watts
Therefore

Test: Communication System - Question 19

A computer puts out binary data at the rate of 56 kbps. The computer output is transmitted using a
baseband binary PAM system that is designed to have a raised cosine spectrum. Determine band width
required if the roll-off factor is 0.5.

Detailed Solution for Test: Communication System - Question 19

Bit Rate (Rb) = 56 Kbps
Since it is transmitted by 2-array,
so minimum bandwidth without
raised-cosine pattern

and minimum bandwidth with
raised-cosine pattern

Test: Communication System - Question 20

A QPSK system transmits binary data at the rate of 2.5 x 106 bit per second. Determine minimum
bandwidth required for the transmission.

Detailed Solution for Test: Communication System - Question 20

Test: Communication System - Question 21

For attenuation of high frequencies we should use

Detailed Solution for Test: Communication System - Question 21

Since Xc for high frequencies is low, the high frequencies are shunted to ground and are not transmitted.

 

Test: Communication System - Question 22

The pulse shown in the figure, is given as the input of a matched filter. Determine the peak value of
the output of matched filter. 

Detailed Solution for Test: Communication System - Question 22

Test: Communication System - Question 23

A binary random variable X takes the value of 1 with probability 2/3. X is input to a binary symetric
channel with cross-over probability 1/2.

Determine the value of H(Y)

Detailed Solution for Test: Communication System - Question 23

Test: Communication System - Question 24

A voice-grade channel of the telephone network has a bandwidth of 3.4 KHz calculate the information capacity of the telephone channel for a signal to noise ratio of 30 dB.

Detailed Solution for Test: Communication System - Question 24

Capacity of a gaussian channel is
given as,

C = BW log2 (1 + SNR)

Here SNR = 30 dB (1000)
So,

Test: Communication System - Question 25

Determine the minimum sampling frequency of x(2t), where x(t) = sine (1000t)

Detailed Solution for Test: Communication System - Question 25

Minimum sampling frequency of
x(t) is 1000 Hz (1KHz)
So, minimum sampling frequency
of x(2t) is 2KHz

Test: Communication System - Question 26

The probability density function of random variable X is given as

Determine the variance (σ2) of random variable X.

Detailed Solution for Test: Communication System - Question 26

Given

Comparing this equation with the
standard gaussian probability
density function
i.e

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