Indian Institute of Technology Madras (IIT-M) 2007 B.Tech Electronics and Communications Engineering COMMUNICATION ENGINEERING - Question Paper

Code: D-12
Time: three Hours
Subject: COMMUNICATION ENGINEERING
Max. Marks: 100


NOTE: There are 11 ques. in all.

ques. one is compulsory and carries 16 marks. ans to Q. 1. must be written in the space given for it in the ans book supplied and nowhere else.
ans any 3 ques. every from Part I and Part II. every of these ques. carries 14 marks.
· Any needed data not explicitly given, may be suitably presumed and said.
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Q.1 select the accurate or best option in the subsequent : (2x8)


a. In a communication system, noise is most likely to affect the signal
(A) at the transmitter.
(C) at the receiver only. (B) in the channel only.
(D) both (B) & (C).
b. The value of resistor creating thermal noise is doubled. The noise power generated is
(A) halved.
(C) doubled. (B) quadrupled.
(D) unchanged.
c. If a carrier in 100% modulated AM wave is suppressed, the percentage power saving will be
(A) 50.
(C) 100. (B) 150.
(D) 66.66.
d. The cladding which surrounds the fibre core
(A) is used to decrease optical interference.
(B) is used to protect the fibre.
(C) acts to help guide the light in the core.
(D) ensures that refractive index remains constant.

e. Quantizing noise occurs in
(A) time division multiplexing.
(C) pulse code modulation.
(B) frequency division multiplexing.
(D) pulse width modulation.

f. The signals sent by TV transmitter to ensure accurate scanning in the receiver are called
(A) sync.
(C) luminance.
(B) chroma.
(D) video.
g. Frequencies in the UHF range normally propagate by means of

(A) ground waves.
(C) surface waves. (B) ) sky waves.
(D) space waves.
h. A pre-emphasis circuit provides extra noise immunity by

(A) boosting the bass frequencies.
(B) pre amplifying the whole audio band.
(C) amplifying higher audio frequencies.
(D) converting the phase modulation to FM.

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PART I
ans any 3 ques.. every ques. carries 14 marks.
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Q.2 elaborate the different forms and sources of noise? discuss.

(7)

The noise output of a resistor is amplified by a noiseless amplifier having a gain of 40 and a bandwidth of 40 KHz. The output of the amplifier is four mV(rms), if the resistor is operated at 27°C. What is its resistance?
(7)

Q.3 Derive the relation ranging from the output power of an AM transmitter and depth of modulation.

(7)
A broadcast transmitter radiates 4.72 KW when the modulation percentage is 60. compute the total power when the modulation has been decreased to 40%.
(7)
Q.4 Draw the block diagram of the Armstrong frequency modulation system. discuss briefly the function of every block.

(14)
Q.5 In connection with space wave propagation, what is radio horizon? discuss how it differs from the optical horizon?
(7)
Briefly define the subsequent terms connected with sky wave propagation
(i) virtual height (ii) critical frequency
(iii) maximum usable frequency.

(7)
Q.6 Draw the block diagram of black and white T.V. Receiver. discuss the function of every block briefly. (14)

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PART II
ans any 3 ques.. every ques. carries 14 marks.
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Q.7 discuss how radiation takes place from an antenna. What is radiation resistance?

(7)

discuss the difference ranging from driven and parasitic elements in an antenna array. What is the difference ranging from Director and Reflector?
(7)

Q.8 discuss the principle of PCM. define a PCM link with the help of a block diagram. discuss how companding improves S/N ratio.

(14)
Q.9 List out the advantages of optical fibre communication.
(7)
Draw and discuss the block diagram of a typical SSB transmitter.
(7)
Q.10 discuss parity and its use in data transmission systems.
(7)
elaborate the various light sources used in fibre optics? define in brief.

(7)
Q.11 discuss the need for satellite communication. State advantages of synchronous satellite communication. discuss multiple access methods. (14)

Earning:   Approval pending.