# Analog communication Dec 2010

(Electronics and Communication Engineering Branch)

Note: Attempt any one question from each unit.

All question carry equal marks.

1. (a)   Prove that following properties of Fourier transform-

(i)        Frequency differentiation theorem.

(ii)      Time integration theorem.

(b)      A signal e-3tu(t) is passed through an ideal low pass filter with cut-off

frequency of one rad per second

(i)       Test wheatear the input is an energy signal

(ii)       Find the output energy

2. (a)   Find the Fourier transform of the following-

(i) cos ωct

(ii) f(t) = { ejt        |t|<1

0        otherwise

(b)        State and prove parseval’s theorem for energy signals.

3. (a)    A signal tone modulating signal em = Emcosωmt amplitude modulates a carrier ec = Eccosωmt.

(i)  Derive an expression for the AM wave e(t).

(ii) Derive an expression for modulation index.

(iii) Draw the AM waveform and its spectrum.

(b)        Explain the synchronous detection method for detection of SSB-SC signal. Also discuss thr effect

of phase and frequency error in synchronous detection.

4. (a)    What are the various method for AM generation ? Explain balanced modulator method in detail.

(b)     Explain envelope detector method for demodulator of AM waves Discuss the choice of time

constant RC. Derive the relation for obtaining optimum value of time constant RC.

5. (a)   A carrier  A cosωmt. is frequency modulated by a single tone modulating signal f(t) = Emcosωmt.

Find the expression for the following:

(i) The FM wave (ii) Expression for narrowband FM.

(B)       Explain with block diagram Armstrong method for FM generation.

6. (a)   Define and diffentiate in detail the following:

(i)  Frequency and phase modulation

(ii)  NBFM and WBFM

(b)        Explain slope detection method for FM detection.

7. (a)   What is difference between AM transmitter employing low level modulation and high level

Modulation? Explain both type of AM transmitter with block diagram.

(b)      Define and explain the receiver characterics of the following:

(i) Selectivity

(ii) Fidelity

(iii) Sensitivity in detail

Also discuss the intermediate frequency selection.

OR

8.       Explain the block diagram the working of FM transmitters. Also discuss the multiplication applied

to FM signal