GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER-V (NEW) EXAMINATION - WINTER 2020
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Subject Code:2151004 Date:05/02/2021Subject Name:Electronic and Communication
Time:10:30 AM TO 12:30 PM Total Marks: 56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.
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2. Make suitable assumptions wherever necessary.3. Figures to the right indicate full marks.
Q.1 (a) Define terms modulation and demodulation with respect to the 03
communication process.
(b) Differentiate passive and active components used to design 04
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communication circuits. Also describe mutual inductance effect. (c) With help of neat diagram describe the working principle of diode 07
envelope detector circuit used for amplitude demodulation process.
Also determine the total power radiated by an antenna, given that
with modulation index 30% a transmitter supplies 8 KW carrier
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signal power to it. Q.2 (a) Comment on bandwidth requirement of a sinusoidal AM and FM 03
wave during its propagation in channel medium.
(b) A sinusoidal carrier signal having amplitude 10 V and frequency 04
1000 KHz is amplitude modulated with sinusoidal information
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signal having amplitude 5 V and frequency. 100 KHz. Calculate (1)power in side bands (2) total power in AM wave.(Assume R=1 ohm)
(c) Explain the trapezoidal method for monitoring the A.M waveform 07
using oscilloscope in detail. Also define term Skin effect.
Q.3 (a) Compare DSB-FC and SSB-SC modulation schemes and prove that 03
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use of SSB technology is preferable as compared to use of DSBtechnology.
(b) Compare FM and AM methods. Also describe the Armstrong method 04
for generating FM waves with help of neat diagram.
(c) An FM wave is described as, e(t) = 10 sin (5 x 103 t + 4 sin 1250 t) 07
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Determine the values of (i) The carrier frequency (ii) Modulatingfrequency (iii) The modulation index and (iv) Carrier frequency
deviation for the same.
Q.4 (a) Describe the significance of synchronous product detector in SSB 03
demodulation process.
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(b) Explain the basic working principle of FM detector. Also describe 04
working of foster seeley discriminator circuit with neat diagram.
(c) Enlist all SSB modulation schemes. Explain the Phasing method for 07
the same.
Q.5 (a) List out basic functions of communication receiver circuit. 03
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(b) Define term tracking with respect to a superhetrodyne receiver. Also 04
explain the three points tracking process used in radio receiver.
(c) Explain briefly about AGC with circuit details.
Q.6 (a) Describe the equations of resonance frequency, Q factor and the -3 dB 03
bandwidth of the series tuned circuits.
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(b) Derive the general Friis’s formula to define noise factor of cascaded 04
amplifiers.
(c) With help of neat general diagram describe the working of a super 07
heterodyne receiver.
Q.7 (a) Mention the significance of series tuned circuit in the communication 03
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process.(b) Describe briefly about the HAM radio 04
(c) State and prove properties of Fourier transform. 07
Q.8 (a) Mention the significance of parallel tuned circuit in the communication 03
process.
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(b) Describe utilization of HAM radio in natural calamities. 04
(c) State the Parseval’s theorem. Also define terms ESD and PSD. 07
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