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Posted Date: 30 Oct 2008 Posted By: satish Member Level: Diamond
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2008 Jawaharlal Nehru Technological University, Hyderabad II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 ANALOG COMMUNICATIONS (Electronics & Telematics) Question paper
Code No: RR221702 Set No. 3
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
ANALOG COMMUNICATIONS
(Electronics & Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) Define the terms and explain x
i. Busy hour
ii. Traffic units
iii. Full availability
iv. Grade of service
(b) What is the difference between
i. Grading and Trunking and
ii. Smooth and pure chance traffic [8+8]
2. (a) Explain filter method of suppressing unwanted sideband.
(b) A SSB-SC transmitter operating at a 16MHz has frequency stability of 1 part
per million. If its transmission is reproduced by a receiver whose stability is
8 part per million, what is the maximum frequency error at the output of the
receiver could have in reproducing the transmission. [16]
3. (a) With a neat circuit diagram explain the principle of operation of reactance
modulator. Derive the expression for equivalent reactance offered by the cir-
cuit. Discuss how it can be used for generating FM wave. [3+5+2]
(b) Explain why heterodyning does not vary the frequency deviation ratio of a
FM signal but frequency multiplication does. [6]
4. (a) Distinguish between negative peak clipping and diagonal peak clipping in an
envelope detector. The output of a diode envelope detector is fed through a
DC blocking capacitor to an amplifying stage, which has an input resistance
of 10 kilo-ohms. If the diode load resister is 5k-ohm, determine the maximum
depth of sinusoidal modulation the detector can handle with out negative peak
clipping.
(b) Consider a composite wave obtained by adding a non coherent carrier Ac cos (2 p fc t + f)
to DSB-SC waveX (t) cos (2 p fc t) whereX (t) is the message waveform. This
composite waveform is applied to ideal envelope detector. Find the resulting
detector out put. Evaluate this for .
i. f = 0 and
ii. f 6= 0 and |X (t)| << Ac [8+8]
5. (a) Explain how frequency stability is achieved in modern transmitter.
(b) Describe with aid of suitable diagram, the principal method of SSB power
generation.
(c) Describe the advantages of a SSB system for high frequency point to point
communication and explain why it is unsuitable for broadcasting. [4+6+6]
6. Write short notes on the following:-
(a) Automatic Gain Control
(b) Diode Detector.
(c) Mixers. [4+5+7]
7. (a) Explain the phenomena of fading in detail.
(b) Describe different diversity reception techniques including the MUSA system
to combat fading. [8+8]
8. Draw the schematic diagram of the modulator-demodulator for FM and prove the
signal to noise power ratio at the demodulator output (SNR)o, fm= 3Ac2kf2p/2NoW3.
fm = 3A2
c Kf2P/2NoW3.
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