Gujarat Technological University 2011-6th Sem B.E , 160802 - Electronic Communication on - Question Paper
GUJARAT TECHNOLOGICAL UNIVERSITY
B E Sem-VI exam May 2011
Subject code: 160802
Subject Name: Electronic Communication
Date:17/05/2011 Time: 10.30 am – 01.00 pm
Total Marks: 70
Seat No. Enrolment No.
GUJARAT TECHNOLOGICAL UNIVERSITY
B E Sem-VI Examination May 2011
Subject Name: Electronic Communication Date:17/05/2011 Time: 10.30 am - 01.00 pm
Total Marks: 70
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) With neat schematic diagram explain the operation of the basic communication 07 system.
(b) Explain briefly what is meant by skin effect and why it is undesirable. What steps 07 must be taken to reduce skin effect in inductors?
Q.2 (a) Explain (with neat diagram) equivalent input noise generators and comparison of 07 BJTs and FETs.
(b) The frequency span to be received by a receiver is from 525KHz to1650KHz.If 07 Cmin of tuning circuit is limited to 50pF by a trimmer of 25pF,calculate the value of padder capacitor, if the maximum value of the variable capacitor is 450pF. The IF used is 465KHz.
OR
(b) A mixer stage has a noise figure of 20dB,and this is preceded by an amplifier that 07 has a noise figure of 9dB and an available power gain of 15dB.Calculate the overall noise figure referred to the input.
Q.3 (a) State and prove following properties of Fourier Transform 07
1. Time Shifting 2.Frequency Shifting 3.Convolution in time domain.
(b) Find the Fourier transform of the periodic signal: x(t)=Cos (2nfot).u(t) 07
OR
Q.3 (a) State and prove the following properties of Fourier Transform: 07
1. Scaling 2.Differentiation in time domain
Also explain the significance of these properties in communication systems.
(b) Explain with block diagram frequency multiplier using PLL and Frequency 07 Synthesizer using PLL.
Q.4 (a) Sketch the waveforms for : 07
1.AM wave 2.DSB-SC wave 3.SSB-SC wave
Compare DSB and VSB techniques.
(b) A coil has a series resistance of 5 ohm, a self capacitance of 7pF,and an inductor 07 of 1 micro Henry. Determine the effective inductance and effective Q-factor when the coil forms part of a series tuned circuit resonant at 25 MHz.
OR
Q.4 (a) Explain waveforms at various points of a super heterodyne Receiver. 07
(b) Explain generation of AM(amplitude modulation) wave using nonlinear 07 property(with neat sketch)
Q.5 (a) State and explain Keplers law in relation to artificial satellites orbiting the earth.
07
07
Explain what is meant by the geostationary orbit and why there is only one such orbit.
(b) Noise immunity of digital messages is better than that of analog messages. Justify .Explain:Bandpass limiter
OR
Q.5 (a) Explain block diagram of double conversion used in communication receivers. 07
(b) Explain capacitive tap with circuit diagram and find transfer impedance. Explain 07 what is meant by polar mount antenna.
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