COMMUNICATION THEORY - May / June 2009 Question Paper

Anna University


Fifth Semester

Electronics and Communication Engineering 


(Regulation 2004)

(Common to B.E. (Part-Time) Fourth Semester — Regulation 2005)

Time : Three hours
Maximum: 100 marks

Answer ALL questions.

PART A  -(10 x 2 = 20 marks)

1. Compute the bandwidth of the Amplitude Modulated signal

2. In a Superheterodyne Receiver used for AM demodulation, the If frequency is 455 KHz. If it is required to receive an AM signal centred around 1050 KHz and bandwidth 10 KHz, give the characteristics of the Image rejectionfilter for a suitable choice of Local oscillator frequency.

3. Obtain the bandwidth of the FM signal

4. What do you understand by FM stereo multiplexing? .

5. A white noise has a power spectral density of —170 dBm/Hz. Calculate the
power at the output of a Band Pass Filter of center frequency 120 MHz and
bandwidth 20 KHz if white noise is fed as the input.

6. Give the characteristics of Shol Noise.

7. Compare the noise performance of AM and FM systems.8. What is threshold effect in FM?

9. Calculate the entropy of the source if the symbol set is (s ,s2,s3,s4 J and the corresponding probabilities are (0.2,0.3,0.05,0.45).

10. State Channel coding theorem.

PART B - (5x16=80marks)

11. (a) Give the method for generation of AM, DSBSC and SSB waves. (16)


(b) (i) Discuss the operation of Costas Loop in detail. (8)

(ii) Draw the block diagram for FDM and explain. (8)

12. (a) Discuss on FM demodulation using PLL. (16)


(b) (i) Give the method of GenerĂ tion of FM signal. (6)

(ii) Derive the expression for the spectrum of a FM signal with single
tone modulation. (10)

13. (a) Give the detailed noise analysis of a SSB receiver using coherent
detection. (16)


(b) Define Narrow b
and noise. List the properties of narrow band noise and 
give a brief explanation of each of them. (16)

14. (a) Derive the expression for the Power spectral density at the output of a FM discriminator when the received signai is corrupted by additive white Gaussian Noise. (16)


(b) (i) Discuss Pre-emphasis and De-emphasis in FM. (6)

(ii) Discuss the threshold effect in an envelope detector used in an AM receiver. (10)

15. (a) Discuss the various techniques used for compression of information. (16)


(b) (i) Define Differential entropy. (2)
(ii) Define Mutual Information. (2)
(iii) What is the relation between Mutual Information and Channel
Capacity? - (1)
(iv) Give the (Shannon-Hartley) information capacity theorem and
discuss the implication of the same in detail. (11)

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