ANALOG COMMUNICATION SYSTEM PAPER 1

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ANALOG COMMUNICATION SYSTEMS/ SYSTEM ANALYSIS & DESIGN (EC 301) 5th Sem. May 2k7
Instructions to Candidates:

• Section A is compulsory.
• Attempt any Four questions from Section B
• Attempt any Two questions from Section C

Section A
( 10 x 2 =20)
1.

• Explain the need of modulation?
• A single tone modulating signal f(f) = Em cos wmt; frequency modulates a carrier A cos wct. Find the frequency deviation.
• Explain capture effect and threshold effect in FM.
• Compare FM and AM from the noise performance point of view.
• What is a limited and why is it used.
• What are the advantages of obtaining AM by method of power conversion?
• Explain how PAM signals are defected using holding circuit.
• Show that coherent FSK is 3 db inferior to coherent PKS system.
• Draw the wave forms for PSK modulated signal for the binary signal 1010.
• What are the advantages of pulse modulation over continuous wave modulation?

Section B
( 4 x 5 =20)

2. Explain with necessary equations and a neat block diagram, the coherent detection of SSB signals.

3. The modulating signal, m(t) = 5 cos p t frequency modulates a carrier, c(t) = 10 cos 108t using a modulator of frequency sensitivity, 10 kHz/ volt. Find the modulation index and approximate bandwidth of the FM signal.

4. Derive the time domain expression of a single tone frequency modulated signal.

5. State and prove sampling theorem for low pass signals.

6. Draw and explain PWM modulator and demodulator circuit.

Section C
( 2 x 10 =20)

7. A narrow band FM has no amplitude variation, inspite of the fact that it has the same frequency components as AM. Justify the statement with phasor diagram.

8. A single tone modulating signal Em cos wmt frequency modulates a carrier A cos wcr. Show that:
(a) The detector output signal to noise ratio is proportional to the square of bandwidth of fM signal.
(b) The figure of merit is given by fm=(3/2) m2f.

9. Write notes on the following:
(a) Single side band BFO receivers
(b) AM detector with AGC
(c) Flat-top PAM.