PTU B.Tech ECE 6th Semester May 2019 71546 COMMUNICATION SYSTEM Question Papers

PTU Punjab Technical University B-Tech May 2019 Question Papers 6th Semester Electronic and Communication Engineering (ECE)

Roll No.
Total No. of Pages : 02
Total No. of Questions : 09
B.Tech.(Electronics & Computer Engg.) (2011 Onwards E-I) (Sem.?6)
Subject Code : BTEL-904
M.Code : 71546
Time : 3 Hrs. Max. Marks : 60
SECTION-A is COMPULSORY consisting of TEN questions carrying T WO marks
SECTION-B contains FIVE questions carrying FIVE marks each and students
have to attempt any FOUR questions.
SECTION-C contains T HREE questions carrying T EN marks each and students
have to attempt any T WO questions.

Answer briefly :

a) List three basic types of analog pulse modulation techniques. Which one is used as an
intermediate step in PCM?

b) What is the purpose of sample and hold circuit?

c) What happens if the multiple massages are transmitted simultaneously without

frequency translation?

d) State the basic requirement of analog communication system that can be met with the

process of modulation.

e) Describe the term over-modulation with the help of diagram.

f) Why is modern communication systems equipped with AGC circuit?

g) What do you understand by coherent and non coherent detection of digital signal?

h) Define the terms selectivity, sensitivity, fidelity and image frequency with suitable


i) Draw block diagram of TRF AM radio receiver. Also state three disadvantages of the
TRF AM radio receiver.

j) How constant frequency is achieved in the super-heterodyne receiver?

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Derive the relationship between the output power of AM transmitter and depth of
modulation and plot it for various values of modulation index from zero to maximum.
How frequency modulation (FM) can be generated from phase modulation (PM)? Also
draw and discuss the narrow band FM and PM generator/modulators.
Discuss the significance of noise triangle. How pre-emphasis and de-emphasis is used to
avoid the effect of noise?
Explain how image frequency signals are received in super-heterodyne receiver. How can
these signals be rejected?
Explain the generation and detection of pulse width modulation and pulse position

In an Armstrong FM transmitter, the narrowband carrier frequency fc1 = 0.1 MHz and
second carrier frequency fc2 =8.5 MHz and output carrier frequency is 100MHz and
f = 75KHz. Calculate multiplying factors n1 and n2 if narrowband frequency deviation is
How sampling takes place in digital communication? Derive mathematical expression to
elaborate the working of sampling. Describe Pulse code modulation.
An FM modulator operates at carrier frequency of 500 KHz with frequency deviation
sensitivity of 1.5 KHz/V. A PM modulator operates at a carrier frequency of 500 KHZ
with phase deviation sensitivity of 0.75 rad/v. both FM and PM modulators are
modulated by the same modulating signal having peak amplitude of 4 V and modulating
frequency of 2 KHz :

a) Is it possible to distinguish the FM spectrum from the PM spectrum?

b) If the modulating frequency is changed to 1 KHz, is it now possible to distinguish the

FM spectrum from the PM spectrum?

NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 04 November 2019