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Code No: V0425/R07 Set No. 1 II B.Tech II Semester Regular Examinations, April 2010 ANALOG COMMUNICATIONS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ? ? ? ? ? 1. (a) Define communication. Explain with block diagram the basic communication system.Write about modern communication system. (b) A carrier wave ofrequency 10 MHz and peak value of 10 V is amplitude modulated by a 5 KHz sine wave of amplitude 6 V. Determine the modulation index and draw the one sided spectrum of modulated wave. [8+8] 2. (a) Explain the DSB-SC generation by balanced modulator using diodes. (b) The modulating signal in an AM-SC system is a multiple-tone signal given by m(t) = A 1 cos ω 1 t + A 2 cos ω 2 t + A 3 cos ω 3 t. The signal m(t) modulates a carrier A c cos ω c t. Plot the single-sided spectrum and find the bandwidth of the modulated signal. Assume that ω 3 > ω 2 > ω 1 and A 1 > A 2 > A 3 . [8+8] 3. A synchronous detection of SSB signalshows phase and frequency discrepancy. ConsiderS(t) = N P i=1 cos [(ω c t) cos(ω i t + Φ i ) − sin(ω c t) sin(ω i t + Φ i )]is an SSB signal. The signalis multiplied by the locally generated carrier cosω c t and then passed through a low-pass filter. (a) Prove that the modulating signal can be completely recovered if the cut-of frequency of the filter is f N < f o < 2f c . (b) Determine the recovered signal when the multiplying signal is cos[ω c + Φ]. (c) Determine the recovered signal when the multiplying signal is cos[(ω c t+∆ω)t]. Give ∆Φ << Φ i where ω c = 2Πf c , ∆ω = 2 Q ∆f. [16] 4. Explain demodulation of FM signal with the help of PLL. [16] 5. It is given the threshold level for AM is equivalent to the input SNR (S/N ) I = 10. Assume this conclusion is also valid for FM. (a) Determine the output SNR at the threshold level for FM (assuming sinusoidal modulation). (b) Determine the modulation index β that produces (S/N)o =30 dB at the thresh- old. [16] 6. (a) Classify radio transmitters in detail. (b) Compare low level modulation and high level modulation of radio transmitters. [16] 1 of 2 Please purchase PDF Split-Merge on .
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Code No: V0425/R07 Set No. 1 7. (a) What are the salient features of broadcast radio receivers ? (b) For a broadcast super heterodyne AM receiver having no RF amplifier, the loaded Quality factor Q of the antenna coupling circuit is 100. Now if the intermediate frequency is 455 kHz, then determine the following : i. the image frequency and its rejection ratio at an incoming frequency of 1000 kHz.
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