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Code No: NR220404

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II B.Tech II Semester Supplimentary Examinations, Apr/May 2009 ANALOG COMMUNICATIONS ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ?????

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1. (a) Draw the cord circuit and explain how a call materialises in a control Battery exchange between two subscribers? (b) Explain with the aid of a neat diagram the subscribers set used in a CB exchange and need for providing antiside tone circuit. [8+8] 2. (a) Explain the balanced modulator using FET amplifiers.

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(b) Compare various methods of SSB generation.

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3. (a) The sinusoidal modulating wave m (t) = Am cos (2πfm t) is applied to a phase modulation with phase sensitivity Kp . The unmodulated carrier wave has frequency fc and amlititude Ac .Determine the spectrum of the resulting phase modulated wave, assuming that the maximum phase deviation βp = Kp Am does not exceed 0.5 radians. (b) A carrier wave of frequency 100 MHz is frequency modulated by sine wave of amplitude 20 volts and frequency 100 KHz. The frequency sensitivity of the modulation is 25 KHz per volt. Determine the approximate bandwidth of FM wave using Carson’s rule. [8+8] 4. (a) Explain the operation of a square law detector and compare it with envelope detector.

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(b) The signal v (t) = (1 + 0.1 cos ω1 t + 0.1 cos 2ω1 t) cos ωc t is detected by a square law detection Vo = 2V2 .Put the amplitude -frequency characteristic of Vo (t). [8+8]

5. (a) Write short notes on the following :-

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i. Harmonic generators. ii. transmitter power supplies.

(b) Explain with suitable block diagram the various stages of a frequency modulated broadcast transmitter. Draw the block schematic of a crystal controlled frequency modulation broadcast station operating on 96.5MHZ.The modulating frequency employed cover the range 60 to 12000 HZ .and a maximum deviation of 75 KHZ is desired. [6+10]

6. (a) Draw the block diagram of AM radio receiver and explain the function of each block.

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Code No: NR220404

(b) Explain what is meant by image frequency. What are the considerations in the choice of IF in a Superheterodyne receiver? [8+8] 7. Write short notes on the following:(a) Receiver measurements.

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(b) Squelch circuits. (c) Noise limiter.

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(b) State the FM threshold effect? (c) What is capture effect?

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8. (a) In FM by what factor does the output SNR improve for each doubling of the transmission bandwidth? Assume small noise. [4x4=16]

(d) For large noise what is the effect of a practical PLL on the threshold region?

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