Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Summer 5th Sem Old 151004 Electronic Communication Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V(OLD) EXAMINATION ? SUMMER 2019
Subject Code:151004 Date:20/06/2019
Subject Name:Electronic Communication
Time:02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Draw the block diagram of a communication system and briefly
describe the function of each block.
07
(b)
List different types of noises in communication systems. Derive and
expression for noise factor for amplifiers in cascade.
07
Q.2 (a) List any five properties of Fourier Transform. Prove any two of them. 07
(b) Draw neat block diagram of a super heterodyne radio receiver and
explain the function of each block.
07
OR
(b) Define the following terms with reference to radio receivers:
Selectivity, Sensitivity, Fidelity, AGC, Tracking, Tuning range and
Spurious responses.
07
Q.3 (a) Define resonance. Draw the circuit of a series resonance circuit. Write
expression for frequency of resonance. Define its Q factor. Express its
impedance in terms of Q. Draw the magnitude of impedance vs. freq.
graph for this circuit. Also, define 3-dB bandwidth.
07
(b) Two resistors of 20 ? and 50k ? are at room temperature. For a
bandwidth of 100 kHz, calculate the thermal noise voltage generated
by (i) each resistor (ii) two resistors in series (iii) the two resistors in
parallel.
07
OR
Q.3 (a) Define mutual inductance. State the use of dot conventions in
inductive circuits. Write expressions for total series inductance, total
parallel inductance, minimum inductance, maximum inductance and
coupling factor for a circuit with mutual inductance.
07
(b) Explain Parseval?s theorem for signal energy. Verify this theorem for
a signal g(t) = e
-at
u(t) (a>0). Also, find Energy spectral density of this
signal.
07
Q.4 (a) A signal m(t) = 3 cos (2 ? 1000 t) is amplitude modulated by carrier
c(t) = 10 cos (2 ? 30,000 t). Find modulation index. Draw spectrum of
modulated signal. Determine the bandwidth of the modulated signal.
Find upper side frequency and lower side frequency. Also, find total
average power of the modulated signal, assuming the power is
delivered to a ohm load resistor.
07
(b) Derive an expression for DSBSC signal for a single balanced FET
modulator circuit.
07
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Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V(OLD) EXAMINATION ? SUMMER 2019
Subject Code:151004 Date:20/06/2019
Subject Name:Electronic Communication
Time:02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Draw the block diagram of a communication system and briefly
describe the function of each block.
07
(b)
List different types of noises in communication systems. Derive and
expression for noise factor for amplifiers in cascade.
07
Q.2 (a) List any five properties of Fourier Transform. Prove any two of them. 07
(b) Draw neat block diagram of a super heterodyne radio receiver and
explain the function of each block.
07
OR
(b) Define the following terms with reference to radio receivers:
Selectivity, Sensitivity, Fidelity, AGC, Tracking, Tuning range and
Spurious responses.
07
Q.3 (a) Define resonance. Draw the circuit of a series resonance circuit. Write
expression for frequency of resonance. Define its Q factor. Express its
impedance in terms of Q. Draw the magnitude of impedance vs. freq.
graph for this circuit. Also, define 3-dB bandwidth.
07
(b) Two resistors of 20 ? and 50k ? are at room temperature. For a
bandwidth of 100 kHz, calculate the thermal noise voltage generated
by (i) each resistor (ii) two resistors in series (iii) the two resistors in
parallel.
07
OR
Q.3 (a) Define mutual inductance. State the use of dot conventions in
inductive circuits. Write expressions for total series inductance, total
parallel inductance, minimum inductance, maximum inductance and
coupling factor for a circuit with mutual inductance.
07
(b) Explain Parseval?s theorem for signal energy. Verify this theorem for
a signal g(t) = e
-at
u(t) (a>0). Also, find Energy spectral density of this
signal.
07
Q.4 (a) A signal m(t) = 3 cos (2 ? 1000 t) is amplitude modulated by carrier
c(t) = 10 cos (2 ? 30,000 t). Find modulation index. Draw spectrum of
modulated signal. Determine the bandwidth of the modulated signal.
Find upper side frequency and lower side frequency. Also, find total
average power of the modulated signal, assuming the power is
delivered to a ohm load resistor.
07
(b) Derive an expression for DSBSC signal for a single balanced FET
modulator circuit.
07
2
OR
Q.4 (a) Draw the block diagram and derive the expression for SSBSC signal
generation using phasing method.
07
(b) Explain the working of envelope detector circuit with neat circuit and
waveforms. Also, list the distortions observed in envelope detector and
the conditions to avoid those distortions.
07
Q.5 (a) Sketch angle ?(t) as a function of time for a 100MHz carrier wave
which is modulated by a 1kHz square wave that has zero DC
component and Vpp = 20 V. The frequency deviation constant is 9
kHz/V. Also, plot instantaneous freq. vs. time and graph and
modulated signal.
07
(b) Draw the block diagram of Armstrong method of FM generation and
explain its working.
07
OR
Q.5 (a) Draw the block diagram of Phase Lock Loop FM- demodulator and
explain its working with relevant equations.
07
(b) Compare AM, FM and PM signals in terms of its power, bandwidth,
time domain waveforms, frequency domain waveforms, number of
sidebands, modulation indexes and equation of modulated signal
considering sinusoidal modulating signal.
07
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This post was last modified on 20 February 2020