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Posted By: ram Member Level: Diamond Posted Date: 03 Sep 2008
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2006 Jawaharlal Nehru Technological University Electronics & computers IV B.Tech. II Semester Regular Examinations, April/May -2006 SATELLITE COMMUNICATIONS Question paper
Code No: RR421901 Set No. 1
IV B.Tech II Semester Regular Examinations, Apr/May 2006
SATELLITE COMMUNICATIONS
(Electronics & Computer Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. List the various advantages and disadvantages of satellite communication. Explain
the various reason for preferring satellites than optical fibers which are providing
very high bandwidth. [16]
2. (a) What is meant by look angles? Explain them with reference to a geostationary
satellite. [8]
(b) Name the orbital aspects which are of importance in synchronous satellite
communication. Explain these aspects. [8]
3. Explain about spacecraft subsystem in detail. [16]
4. Explain the operation of (14/12)GHz communication systems, with a neat block
diagram. [16]
5. (a) What is the implication of G/T being negative. [3]
(b) An earth station antenna has a diameter of 30m, has an overall efficiency
of 68% and is used to receive a signal at 4150 MHZ. At this frequency the
system Noise temperature is 79k when the antenna points at the satellite an
elevation angle of 280 . What is the earth station G/T under these conditions?
If heavy rain causes the sky temperature to increase so that the system noise
temperature noise to 88k, what is the new G/T value? [8]
(c) List the salient details of INTELSAT-IV down link specification. [5]
6. (a) What is meant by communication resource? What are the similarities and
differences between the terms Multiplexing and Multiple Access ? [8]
(b) A TDMA system operates at 100 Mbits/s with a 2 ms frame time. Assume
that all slots are of equal length and that a guard time of 1ยต s is required
between slots. Compute the efficiency of the communications resource (CR)
for the case of 1, 2, 5, 10 slots per frame. [8]
7. (a) A 14/11 GHz antenna has a G/T ratio of 40.3dB at 11.2 GHz. The antenna
gain is 64dB and the system noise temperature at 10 deg elevation angle
in clear air conditions is 234k. The antenna aperture efficiency and noise
temperature are detailed in the list below. During heavy rain, the slant path
attenuation reaches 8dB for 0.01 percent of the year. Calculate G/T ratio
for their fraction of the year and the corresponding reduction in C/N for the
received signal. [10]
Aperture efficiency: 71.3%
Sky noise at 10deg elevation: 30k
LNA noise temperature: 150k
(b) Explain in detail how geostationary satellites are tracked from the earth sta-
tion? [6]
8. Analyse various noises disturbing the received signal from satellite at earth station.
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