Rashtrasant Tukadoji Maharaj Nagpur University 2009 B.E Electronics & Communication Engineering Winter , Faculty of Engineering and Technology, COMMUNICATION ELECTRONICS - Question Paper

part A

1. (a) explain the types, causes and effects of different forms of noise which may be created within a receiver.
(b) discuss Noise temperature and discuss the method for measuring the Noise figure of receiver or an amplifier.

2. (a) An audio frequency signal 10sin??2p*500t? is used to amplitude a carrier of 50sin??2p*?10?^5 t.? Calculate:
(i) Modulation index
(ii) Total power delivered to the load of 600O
(iii) Transmission efficiency
(iv) Representation of AM wave in frequency Domain.
(b) Distinguish ranging from low level modulation technique and high level modulation technique. Draw a schematic block diagram of any low level modulation method and discuss in brief.

3. (a) discuss SSB modulation.
(b) discuss any SSB modulation technique in detail with its advantages and disadvantages.
(c) A 400 watt carrier is modulated to a depth of 80%. compute the total power in the single side band modulated wave.

4. (a) What is need of employing a Pre-emphasis and de-emphasis in an FM system?
(b) explain the effect of noise on carrier in an FM system.
(c) Derive the expression for sinusoidal carrier voltage which has been frequency modulated by a different sinusoidal modulating voltage.

5. (a) Using Carsons Rule estimate the maximum Bandwidth needed for an FM broadcast system if maximum deviation allowed is 75kHz and maximum modulation frequency allowed is 15kHz.
(b) What is meant by the term significant sideband in FM system?
(c) discuss the principle of Armstrong kind of frequency modulator.

part B

6. (a) discuss in detail the generation, Demodulation, advantages and disadvantages of PCM.
(b) What is companding? Why it is used? Illustrate your ans with a neat sketch of typical companding curve.

7. (a) Draw block diagram for superheterodyne Radio receiver and briefly discuss function of every block. elaborate the advantages of this receiver over TRF receiver?
(b) compute the image rejection ratio of a receiver having RF amplifier and an IF of 450 kHz, Qs of relevant coils are 65 and for incoming frequency:
(i) 1200kHz
(ii) 20MHz.

8. (a) Using circuit diagrams, discuss the operation of the self excited transistor mixer.
(b) Draw the transistorised circuit of an IF amplifier in a superheterodyne receiver and discuss its operation. Also discuss the necessity of neutralising transistor tuned amplifier.

9. (a) elaborate the various kinds of manual exchanges? Why are they so called? Compare the merits and demerits of local battery exchange.
(b) What is line telephony? elaborate its area of applications?

10. Write short notes on any THREE:
(i) Quantizing Noise
(ii) Time Slot Interchanging
(iii) PAM
(iv) Image frequency Signal Rejection
(v) FM Radio Receiver.

Earning:   Approval pending.