# RGPV question paper BE 4th Sem Analog and digital communication Dec 2011

RGPV question paper – BE (fourth semester) -Analog and digital communication -Dec,2011

B.E. (fourth semester) EXAMINATION, Dec, 2011

(New scheme)

(Electronics and Communication Engg. Branch)

Analog and digital communication

EC-405

Note:   Attempt any one question from each unit. All question carry equal marks.

1.(a)    Find the Fourier transform of a radio frequency pulse  shown in fig.

(b)       Explain causal and non causal system in short.

2. (a)   Explain parseval’s theorem for energy signals.

(b)      State and prove the frequency convolution theorem.

3. (a)  Draw and explain the working of envelope detector circuit.

(b)      What is need of modulation in communication system?

OR

4.       Explain the working of DSB-SC with block diagram, modulated signal and its spectrum. What is the

effect of phase and frequency error in synchroun detection, and how we can remove its.

5. (a)  Derive an expression for an FM signal when a carrier A sinωc t is being modulated by a signal :

(i)      Em cos ωmt

(ii)     Em sin ωmt

(b)    Explain capture effect in FM transmission.

6.(a)      Draw and explain the working of PPL detectors.

(b)       A signal tone FM signal is given by :

Efm = 10 sin (6π×106t+20sin2π×103t)

Find modulation index, modulating frequency, carrier frequency and power of FM signal.

7. (a)  Draw the block diagram of super heterodyne receiver and explain its working , with tracking and

alignment process.

OR

8. (a)   What is AVC an AFC ? What is the impact of AVC and AFC in radio transmitter?

(B)    Draw and explain AM transmitter using low level modulating.

9. (a)  Write short notes on two of the following :

9(i)    Noise bandwidth

(ii)      Noise figure

(iii)     Noise temperature

(iv)     Noise in angel modulation system

OR

10 (a) Explain figure of merit for FM.

(b)  Discuss white noise and its power spectrum. Which frequency components does it have?