EC2252 Communication Theory Question banks 2marks and 16 marks

Anna university question banks for fourth (4th) semster ece 2m and 16

Electronics and Communication Engineering

EC2252 Communication Theory Question banks 2marks and 16 marks

EC2252 Communication Theory Question banks 2marks and 16 marks

Fourth Semester Electronics and Communication Engineering

EC2252 Communication Theory

Anna University

B.E./B.Tech.Degree Examinations,Apr/May 2010

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Regulations 2008

Fourth Semester

Electronics and Communication Engineering

EC2252 Communication Theory

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Time: Three Hours

Maximum: 100 Marks

Answer ALL Questions

Part A - (10 x 2 = 20 Marks)

1. How many AM broadcast stations can be accommodated i n a 100 kHz bandwidth if t he highest frequency modulating a carrier i s 5 kHz?

2. What are the causes of linear distortion?

3. Draw t he block diagram of a method for generating a narrowband FM signal.

4. A carrier wave of frequency 100 MHz i s frequency modulated by a signal 20 sin(200π × 103t).

What i s bandwidth of FM signal if the frequency sensitivity of t he modulation is 25kH z/V .

5. When i s a random process called deterministic?

6. A receiver connected to a n antenna of resistance of 50Ω has an equivalent noise resistance of 30Ω. Find the receiver noise figure.

7. What are t he characteristics of super heterodyne receivers?

8. What a re the methods to improve FM threshold reduction?

9. Define entropy function.

10. Define Rate Bandwidth an d Bandwidth efficiency.

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Part B - (5 x 16 = 80 Marks)

11. (a) (i) Draw an envelope detector circuit used for demodulation of AM an d ex- plain its operation. (10)

(ii) How SSB can be generated using Weaver’s method? Illustrate with a neat block diagram. (6)

OR

11. (b) (i) Discuss i n detail about frequency translation and frequency division multiplexing technique with diagrams. (10)

(ii) Compare Amplitude Modulation and Frequency Modulation. (6)

12. (a) (i) Using suitable Mathematical analysis show that FM modulation produces infinite sideband. Also deduce an expression for the frequency modulated output and its frequency spectrum. (10)

(ii) How can you generate an FM from PM and PM from FM? (6)

OR

12. (b) (i) A 20 MHz i s frequency modulated by a sinusoidal signal such that t he maximum frequency deviation is 100 kHz. Determine the modulation index and approximate bandwidth of t he FM signal for t he following modulating signal frequencies,

(1) 1 kHz (2) 100 kHz and (3) 500 kHz. (8)

(ii) Derive the time domain expressions of FM and PM signals. (8)

13. (a) (i) Give a random process, X (t) = A cos(ωt + θ), where A an d ω a re constants and θ i s a uniform random variable. Show that X (t) is ergodic in both mean and autocorrelation. (8)

(ii) Write a short note on shot noise and also explain about power spectral density of shot noise. (8)

OR

13. (b) Write t he details about narrow band noise and t he properties of quadrature components of narrowband noise. (16)

14. (a) Derive a n expression for SNR at input (SNRc ) and output of (SNRo) of a coherent detector. (16)

OR

14. (b) (i) Explain pre-emphasis and De-emphasis i n detail. (10)

(ii) Compare the performances of AM and FM systems. (6)

15. (a) (i) Find the code words for five symbols of t he alphabet of a discrete memory- less source with probability {0.4, 0.2, 0.2, 0.1, 0.1}, using Huffman coding and determine the source entropy and average code word length. (10)

(ii) Discuss the source coding theorem. (6)

OR

15. (b) (i) Derive t he channel capacity of a continuous band limited white Gaussian noise channel. (10)

(ii) Discuss about rate distortion theory. (6)

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Anna University

B.E / B.Tech. DEGREE EXAMINATION, MAY/JUNE 2009.

Fifth Semester

Electronics and Communication Engineering 

EC 1301— COMMUNICATION THEORY 

(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)

Or

(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)

Or

(b) (i) Give the method of Generàtion 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)

Or

(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)

Or

(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)

Or

(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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