Rashtrasant Tukadoji Maharaj Nagpur University 2011 B.E Electronics & Communication Engineering Faculty of Engineering and Technology, COMMUNICATION ELECTRONICS - Question Paper

part A

1. (a) What do you mean by the term noise used in communication system?
F=1+(F2-F1)/A1 +(F3-1)/(A1A2 )+(F4-1)/(A1A2A3 )+?
(b) A receiver is connected to an antenna whose resistance is 60O has an equivalent noise resistance of 30O. compute the receivers noise figure in decibels and its equivalent noise temperature.

2. (a) discuss ground wave propagation in detail.
(b) A taxi company uses a central dispatcher with an antenna at the top of 15m tower, to communicate with taxi cabs. The taxi antennas are on the roofs of the cars, approximately 1.5m above the ground. compute the maximum communication distance:
(i) ranging from the dispatcher and the taxi.
(ii) ranging from 2 taxis.

3. (a) Draw the block diagram of phase shift method of SSB generation and discuss how the carrier and the unwanted sideband are suppressed.
(b) The antenna current of an AM transmitter is 8A IF only the carrier is sent, but it increases to 8.93A, if the carrier is modulated by a single sinusoidal wave. Determine the percentage modulation. Also obtain the antenna current of the percent of modulation modifications to 0.8.

4. (a) discuss the Armstrong method for the generation of wideband FM with suitable diagram.
(b) A carrier wave is amplitude 10V and frequency 100MHz is frequency modulated by a sinusoidal voltage. The modulating voltage has an amplitude of 5V and frequency 20KHz. The frequency deviation constant is 2KHz/volt. Draw the frequency spectrum of FM wave.

5. (a) What is threshold effect in an envelope detector? discuss.
(b) Compare performance of FM and AM systems.

part B

6. (a) elaborate the salient features of Broadcast radio receiver?
(b) For a broadcast super heterodyne AM receiver having no RF amplifier, the loaded quality factor Q of the antenna coupling circuit is 100. Now if the intermediate frequency is 455KHz, then determine the following:
(i) The image frequency and its rejection ratio at an incoming frequency of 1000 KHz.
(ii) The image frequency and its rejection ratio at an incoming frequency of 25 MHz.

7. (a) With the help of neat diagrams discuss the transmitter and receiver of pulse code modulation.
(b) A PCM system uses a uniform quantizer followed by 7bit binary encoder. The bit rate of the system is equal to 50*106 bits/sec.
(i) What is the maximum message signed bandwidth for which the system operates satisfactorily?
(ii) compute the output signal to quantization noise ratio when a full load sinusoidal modulating wave of frequency 1MHz is applied to the input.

8. (a) discuss Delta modulation in detail with suitable diagram. Also, discuss ADM and compare its performance with DM.
(b) Compare PAM, PPM and PWM based on subsequent points:
(i) Waveform generated
(ii) Relation of pulse parameters with modulating signal
(iii) Bandwidth
(iv) Power of transmitter
(v) Noise interference

9. (a) discuss Intersymbol interference in detail.
(b) discuss the working of communication receiver with the help of block diagram.

10. Write tech. notes on any 2 of the following:
(i) Central Battery Exchange
(ii) Nuetralization.
(iii) Time slot interchanging.

Earning:   Approval pending.