GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-V (OLD) EXAMINATION - WINTER 2018
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Subject Code:151004 Date: 11/12/2018
Subject Name: Electronic Communication
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) What is noise? Explain thermal noise. [07]
(b) Explain Communication system with the help of block diagram [07]
Q.2 (a) What is modulation? Explain the need of modulation. [07]
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(b) Two resistors of 20 K and 50 K are at room temperature of 15 degree Celsius. for a given bandwidth of 10MHz, determine the thermal noise voltage generated by:a) two resistors in series
b) two resistors in parallel [07]
OR
Q.2 (b) A mixer circuit has a noise figure of 12 dB. It is preceded by an amplifier that has an equivalent noise temperature of 200K and a power gain of 30 dB. Calculate the equivalent noise temperature of combination referred to amplifier input. [07]
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Q.3 (a) Explain the Superhetrodyne receiver with block diagram. [07]
(b) Explain envelop detector for AM demodulation. [07]
OR
Q.3 (a) What is AGC? Explain simple AGC and delayed AGC with proper diagram. [07]
(b) Explain Adjacent channel selectivity and image frequency rejection. [07]
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Q.4 (a) Compare AM, FM and PM [07]
(b) List all the properties of Fourier transform. State and prove time Shifting property. [07]
OR
Q.4 (a) Find the Fourier transform of the signal: x(t) = e-t sin(?t) [07]
(b) Define Amplitude Modulation. Derive the expression for AM modulated wave. [07]
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Q.5 (a) Give difference between SSB and VSB. Explain filter method with necessary block diagram. [07]
(b) Explain parallel tuned circuit and derive equation for resonant frequency and Q-factor. [07]
OR
Q.5 (a) Explain Series tuned circuit and derive equation for resonant frequency and Q-factor. [07]
(b) Explain phase shift method of SSB generation with necessary block diagram. [07]
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