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Posted Date: 08 Jun 2012 Posted By:: Niral Patel Member Level: Gold Points: 5 (Rs. 1)
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2009 Rashtrasant Tukadoji Maharaj Nagpur University B.E Electronics & Communication Engineering Winter 2009, Faculty of Engineering and Technology, COMMUNICATION ELECTRONICS Question paper
Section A
1. (a) Discuss the types, causes and effects of various forms of noise which may be created within a receiver.
(b) Explain Noise temperature and explain 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 between low level modulation technique and high level modulation technique. Draw a schematic block diagram of any low level modulation method and explain in brief.
3. (a) Explain SSB modulation.
(b) Explain any SSB modulation technique in detail with its advantages and disadvantages.
(c) A 400 watt carrier is modulated to a depth of 80%. Calculate 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) Discuss the effect of noise on carrier in an FM system.
(c) Derive the expression for sinusoidal carrier voltage which has been frequency modulated by another sinusoidal modulating voltage.
5. (a) Using Carsons Rule estimate the maximum Bandwidth required 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) Explain the principle of Armstrong type of frequency modulator.
Section B
6. (a) Explain in detail the generation, Demodulation, advantages and disadvantages of PCM.
(b) What is companding? Why it is used? Illustrate your answer with a neat sketch of typical companding curve.
7. (a) Draw block diagram for superheterodyne Radio receiver and briefly explain function of each block. What are the advantages of this receiver over TRF receiver?
(b) Calculate 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, explain the operation of the self excited transistor mixer.
(b) Draw the transistorised circuit of an IF amplifier in a superheterodyne receiver and explain its operation. Also explain the necessity of neutralising transistor tuned amplifier.
9. (a) What are the different types of manual exchanges? Why are they so called? Compare the merits and demerits of local battery exchange.
(b) What is line telephony? What are 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.
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