EC2252 Communication Theory B.E Model Question Paper : aalimec.ac.in

Name of the College : Aalim Muhammed Salegh College of Engineering
University : Anna University
Department : Electronics and Communication Engineering
Subject Code/Name : EC 2252 Communication Theory
Degree : B.E
Year : II
Document Type : Model Question Paper
Website : aalimec.ac.in

Download: https://www.pdfquestion.in/uploads/aa…2-Model-CT.pdf

Aalim Communication Theory Question Paper

Part A

(10 x 2 = 20 marks)
1. What are the advantages of Vestigial Side Band?
2. Compute the bandwidth of the Amplitude modulated signal given by S(t)= 50 [1+0.7 cos (350t)]cos(270000

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3. Distinguish between narrow band FM and wide band FM.
4. What is meant by detection? Name the methods for detecting FM signals.
5. Write the Rayleigh and Rician probability density functions.
6. What is white noise? State its power spectral density.
7. Compare the noise performance of DSBSC receiver using coherent detection with AM receiver using envelope detection.
8. What are the methods to improve FM threshold reduction?
9. Define entropy function.
10. Differentiate between lossless and lossy coding.

11. Compare AM, DSB-SC, SSB and VSB wave?
12. Define modulation index of AM signal..
13. Compare Frequency and Phase modulation.
14. Convert NBFM to WBFM?
15. Define noise figure.
16. Define Thermal noise.
17. Define Figure of merit.
18. Define pre-emphasis and de-emphasis
19. What is channel redundancy?
20. State Shannon’s theorem.

Part B

(5 x 16 = 80 marks)
11. (a) With a help of a neat diagram, explain the operation of an envelope detector. Why does negative peak clipping take place? (16)
(or)
(b) (i) Compare the characteristics of DSBFC, DSBSC, SSBSC, VSB schemes. (4)
(ii) Explain the concept of FDM with a suitable block diagram. (6)
(iii) The antenna current of an AM transmitter is 8 ampere when only the current is sent. The current increases to 8.39 A when carrier is modulated by a signal sine wave. Find the percentage modulation (4)

12 (a) (i) Derive the expression for the single tone frequency modulation and draw its frequency spectrum. (8)
(ii) An angle modulated wave is described by the equation V (t) = 10 cos(2 x106pt + 10 cos 2000pt). Find (1) Power of the modulated signal (2) Maximum frequency deviation (3) Bandwidth. (8)
(or)
(b) (i) A 100 kHz carrier is frequency modulated to produce a peak deviation of 800 Hz. This FM signal is passed through a 3 by 3 by 4 frequency multiplier chain, the output of which is mixed with an oscillator signal and the difference frequency taken as the new output. Determine the frequency taken as the new output. Determine the frequency of the oscillator required to produce a 100 kHz FM output and the peak deviation of the output. (4)
(ii) With necessary diagrams explain the operation of slope detector for demodulating FM signal. (12)

13. (a) State and prove four properties of Gaussian process.
(or)
(b) (i) Derive the expression for shot noise, its mean, autocorrelation & Power density spectrum. (10)
(ii) Consider two amplifiers are connected in cascade. First stage amplifier has gain and noise figure as 10 dB and 2 dB. Second stage has noise figure of 3 dB. Calculate total noise figure. (6)

14. (a) (i) Sketch the block diagram of DSB-SC/AM system and derive the figure of merit. (8)
(ii) Using superheterodyne principle, draw the block diagram of AM radio receiver and briefly explain it. (8)
(or)
(b) (i) Derive the figure of merit of a FM system . (10)
(ii) Compare the performances of AM and FM systems. (6)

15. (a) Using Huffman code I, encode the following symbols. (8)
S = [0.3, 0.2, 0.25, 0.12, 0.05, 0.08,] Calculate (i) Average codeword length , (ii) Entropy of the source
(iii) Code efficiency and (iv) Redundancy (8)
(or)
(b) (i) State and prove the properties of mutual information. (10)
(ii) The channel transition matrix is given by ·
0.9 0.1
0.2 0.8
Draw the channel diagram and determine the probabilities associated with outputs assuming equi probable inputs.