Cochin University of Science and Techology (CUST) 2005-2nd Year B.Tech Electronics and Communications Engineering communication engineering - Question Paper

UNIVERSITY ques. PAPER
MAY 2005


1. a) Why digital communication is superior to analog communication? discuss. List its
advantages.


b) discuss the terms.

1) Continuous spectra and discrete spectra.
2) Signal to noise ratio and noise figure.

OR

2. a) explain the types, causes and effect of different forms of noise in communication
systems.

b) Write notes on frequency spectra of non-sinusoidal waveforms.

3. a) describe AM modulation. Derive an expression for power contained in an AM signal.

b) A 500 KHz RF signal is amplitude modulated with a 5KHz AF signal. The
modulated carrier voltage is 25V maximum and 15V minimum across a 300n
resistive load. Determine 1. Zero modulation RF carrier voltage
2. Modulation index
3. Carrier power
4. Sideband power
5. Upper side band frequency
6. lower side band frequency

c) What is the advantage of using trapezoidal trend to evaluate AM envelope?

4. a) discuss frequency modulation of a sinusoidal wave form and comment on its side
bands.

b) In an FM system, when the audio frequency is 500Hz and the AF voltage is 2.4V,
the deviation is 4.8KHz. If the AF voltage is now raised to 7.2V, what is the new
deviation? If the AF voltage is now raised to 10V while the AF is dropped to
200Hz, what is the deviation? obtain modulation index in every case?

c) discuss the relation ranging from FM and PM with the help of mathematical
expression.

5. a) Using block diagram discuss the “Third” method of SSB generation.

b) Draw the block diagram of an ISB transmitter operating at 22.275MHz without a
pilot carrier and with 2 3KHz sidebands.

c) describe and define VSB. What is its application?

OR

6.a) With the help of a block diagram discuss indirect method of FM generation.

b) discuss the working of an FM stereo transmitter.

7.a) discuss with circuit schematic a typical Foster-Seeley discriminator.

b) What is meant by pre-emphasis and de-emphasis? discuss with circuit schematic.

OR

8. a) Briefly discuss the double tuned super heterodyne receivers. elaborate the
advantages of super heterodyne receivers over TRF receivers?

b) Write short notes on:
1. Image frequency and its rejection
2. Carrier thresholding
3. Capture effect

9. a) discuss various kinds of signaling.

b) discuss the various kinds of tones used in automatic telephony.

OR

10. a) Briefly define the various telegraphic codes.

b) discuss traffic load and grade of service in a telephone system.


-----------------------------------------

Earning:   Approval pending.