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Code No: R5220406 R5II B.Tech II Semester(R05) Supplementary Examinations, December 2010

ANALOG COMMUNICATIONS(Electronics & Communication Engineering)

Time: 3 hours Max Marks: 80Answer any FIVE Questions

All Questions carry equal marks

1. (a) Explain operation of square law detector with circuit diagram and waveforms.

(b) An AM transmitter has un-modulated carrier power of 10 KW. It can be modulated by sinusoidalmodulating voltage to a maximum depth of 40%, without overloading. If the maximum modula-tion index is reduced to 30% what is the extent up to which the un modulated carrier power canbe increased to avoid over loading. [8+8]

2. (a) Considering the modulating and carrier waves as sinusoids, Explain the single tone modulationand demodulation of DSB-SC wave with necessary expressions, waveforms and spectrums.

(b) Find the % power saved in DSB-SC system while compared to AM system. [12+4]

3. A synchronous detection of SSB signal shows phase and frequency discrepancy. ConsiderS(t) =N

i=1

cos[(ct)cos(it + i) sin(ct)sin(it + i)]is an SSB signal. The signal is multiplied by the

locally generated carrier cosct and then passed through a low-pass filter.

(a) Prove that the modulating signal can be completely recovered if the cut-off frequency of the filteris fN < fo < 2fc.

(b) Determine the recovered signal when the multiplying signal is cos[c + ].

(c) Determine the recovered signal when the multiplying signal is cos[(ct+)t]. Give