Rashtrasant Tukadoji Maharaj Nagpur University 2009 B.E Electronics %26amp%3B Communication Engineering Summer %2C Faculty of Engineering and Technology%2C COMMUNICATION ELECTRONICS - Question Paper

part A

1. (a) What is noise? elaborate different forms and sources of noise?
(b) The noise figure of an IF amplifier is 15dbs. The amplifier is preceded by a pre-amplifier with a gain of 10dbs and noise figure of 6dbs. obtain the overall noise figure.

2. (a) discuss ionospheric communication depend on the time of the day and the season? Are there any other periodic effects? Mention them.
(b) The antenna of a TV transmitter is located at a height of 500feet above ground level. compute the distance over which direct ray coverage is possible if the height of a receiving antenna is to be 30 feet.
(c) Draw basic block diagram of communication system

3. (a) discuss Armstrongs system of generating FM waves.
(b) A certain AM transmitter is coupled to an antenna. The input power to the antenna is measured through monitoring the antenna current. With no modulation the current is 10.8A. With modulation, the current rises to 12.15A. Determine the depth of modulation explaining the significance of the formula used.

4. (a) Draw the circuit of a Ratio Detector and discuss its principle of operation in detail.
(b) Derive an expression for the figure of merit of an AM system of envelope detector. elaborate the drawbacks of such a detector?

5. (a) define Weavers method of sideband suppression in SSB system.
(b) What is pre-emphasis? Why is pre-emphasis needed in a radio transmitter.

part B

6. (a) discuss how quantisation noise and channel bandwidth are related in PCM?
(b) discuss the principle of PCM. define a PCM link with the help of block diagram. discuss how compounding improves S/N ratio? elaborate the advantages of Delta modulation over conventional PCM?

7. (a) elaborate the important characteristics of a radio receiver? How are they measured and expressed?
(b) What is the purpose of AVC in a radio receiver? discuss a typical circuit to give AVC in a receiver.

8. (a) When a superheterodyne receiver is tuned to 555kHz, its local oscillator provides the mixer of an input at 1010kHz.What is the image frequency? The antenna of this receiver is connected to the mixer via a tuned circuit whose loaded Q is 40. What will be the rejection ratio of the computed image frequency?
(b) discuss the subsequent terms:
(i) Sensitivity
(ii) Selectivity
(iii) Fidelity.

9. (a) discuss time division multiplexing used in telephony.
(b) Draw the block diagram of communication receiver and discuss the working of squelch system block in detail.

10. (a) Write short notes on any 2 of the following:
(a) ISB transmission
(b) Neutralization
(c) Central switching system.

Earning:   Approval pending.