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Posted By: Lenin Member Level: Diamond Posted Date: 02 Jun 2008
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2007 Indian Institute of Technology Chennai B.Tech Electronics & Communications Engineering COMMUNICATION ENGINEERING University Question paper
Code: D-12
Time: 3 Hours
Subject: COMMUNICATION ENGINEERING
Max. Marks: 100
NOTE: There are 11 Questions in all.
Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
_____________________________________________________________________
Q.1 Choose the correct or best alternative in the following : (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 reduce 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 correct 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.
___________________________________________________
PART I
Answer any THREE Questions. Each question carries 14 marks.
_____________________________________________________
Q.2 What are the various forms and sources of noise? Explain.
(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 4 mV(rms), if the resistor is operated at 27°C. What is its resistance?
(7)
Q.3 Derive the relation between 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. Calculate the total power when the modulation has been reduced to 40%.
(7)
Q.4 Draw the block diagram of the Armstrong frequency modulation system. Explain briefly the function of each block.
(14)
Q.5 In connection with space wave propagation, what is radio horizon? Explain how it differs from the optical horizon?
(7)
Briefly describe the following 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. Explain the function of each block briefly. (14)
___________________________________________________
PART II
Answer any THREE Questions. Each question carries 14 marks.
_____________________________________________________
Q.7 Explain how radiation takes place from an antenna. What is radiation resistance?
(7)
Explain the difference between driven and parasitic elements in an antenna array. What is the difference between Director and Reflector?
(7)
Q.8 Explain the principle of PCM. Describe a PCM link with the help of a block diagram. Explain how companding improves S/N ratio.
(14)
Q.9 List out the advantages of optical fibre communication.
(7)
Draw and explain the block diagram of a typical SSB transmitter.
(7)
Q.10 Explain parity and its use in data transmission systems.
(7)
What are the different light sources used in fibre optics? Describe in brief.
(7)
Q.11 Explain the need for satellite communication. State advantages of synchronous satellite communication. Explain multiple access methods. (14)
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