07 Rr410406 Satellite Communications

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Code No: RR410406 Set No. 1

IV B.Tech I Semester Regular Examinations, November 2007SATELLITE COMMUNICATIONS

( Common to Electronics & Communication Engineering and Electronics &Telematics)

Time: 3 hours Max Marks: 80Answer any FIVE Questions

All Questions carry equal marks⋆ ⋆ ⋆ ⋆ ⋆

1. Explain in detail about India?s participation in other International communicationssatellite systems. [16]

2. (a) What is transfer orbit and how is the orbit correction for the launch of satelliteat latitude other than equator is obtained? [6]

(b) Explain as to how satellite is placed into geostationary orbit from earth. [10]

3. (a) What is spin stabilization? Why is it necessary? Explain various effects thatis to be avoided and its remedial solution. [8]

(b) What is station keeping? Explain various methods of station keeping. [8]

4. Why lens antennas are preferred for satellite communication, explain in detail.Explain the function of lens antenna. [16]

5. (a) What is the necessity of keeping front end of the satellite receiver at theearth station in a helium-coolent: what is the range of temperature of thepreamplifier. [6]

(b) A transponder using the global beam, a typical output back off level of 3dBwith one access to that transponder so the radiated power from the transpon-der is 5dBW giving EIRP of 21dBW. at 40,000kM. The threshold of C/Nis 11dB. Allowing a 7dB system margin. Calculate the diameter of the diskantenna assuming an antenna efficiency of 65% . Assume any data missing.

[10]

6. (a) A 36 MHz satellite transponder is accessed by sequence-synchronous CDMAusers with bit rate 9.6 kbps. Gold sequences with a length of m=10 are used.The link carrier-to-noise plus interference ratio is C/N = - 8 dB. Assume PSKis used as carrier modulation. Find the number of users the transponder canaccommodate at Pe= 10−5. [8]

(b) Consider a fast-hop FSK-FH-CDMA satellite channel where M hops are per-formed per bit. The number of frequency slots in the channel is n. Find theprobability of intercepting k users in one bit interval. [8]

7. (a) What is Faraday rotation? How is it avoided in Satellite communication?

Explain which type of antenna is preferred to avoid it. [8]

(b) How do you select the site for earth station? Explain in detail. [8]

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8. Analyse various noises disturbing the received signal from satellite at earth station.[16]

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1. List the various advantages and disadvantages of satellite communication. Explainthe various reason for preferring satellites than optical fibers which are providingvery high bandwidth. [16]

2. (a) Prove that the smallest value that the inclination angle can have is equal tothe latitude of the launch site in the plane of the orbit. [8]

(b) A satellite is in a circular equatorial orbit at an altitude of 10000 km fromearth’s surface. Determine the maximum eclipse time in a day during the fulleclipse period. [8]



4. Explain in detail about (6/4)GHz communication subsystem. [16]

5. (a) What is the necessity of keeping front end of the satellite receiver at theearth station in a helium-coolent: what is the range of temperature of thepreamplifier. [6]


[10]

6. Explain the Frequency Division Multiple Access of Satellite System with one ex-ample. [16]

7. (a) What are various feed systems employed for large cassegrain antennas. Explainthem clearly. [8]

(b) What are various aspects considered in the design of large antennas? Explainin detail. [8]

8. (a) Explain how the power level of the signal is raised in satellite communication?

Which device is used for power rising? And write its function. [8]

(b) Explain the operation of TWT amplifier? Explain its structure required forreliable operation? [8]

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1. List the various frequency bands being used in satellite communication. Comparethe advantages and disadvantages of different bands considering the effects of prop-agation media. [16]

2. Discuss the phenomena of eclipse as applied to geostationary satellite and solarinterference experienced at an earth station. How do these factors influence thesystem design. [16]



4. Explain about the various effects and their remedies of external satellite environ-ment around satellite antenna. [16]

5. (a) Derive the general link design equation for a satellite and prove that a largeG/T ratio provides better C/N ratio. [10]

(b) A satellite at a distance of 36,000 km from earth radiates a power of 5W froman antenna with a gain of 16dB. Find the power received by an earth stationantenna with a gain of 45dB. Operating frequency is 11GHZ. [6]

6. (a) A 36 MHz satellite transponder is accessed by sequence-synchronous CDMAusers with bit rate 9.6 kbps. Gold sequences with a length of m=10 are used.The link carrier-to-noise plus interference ratio is C/N = - 8 dB. Assume PSKis used as carrier modulation. Find the number of users the transponder can

accommodate at Pe= 10−5

. [8](b) Consider a fast-hop FSK-FH-CDMA satellite channel where M hops are per-

formed per bit. The number of frequency slots in the channel is n. Find theprobability of intercepting k users in one bit interval. [8]

7. (a) What is an orthomode transducer? In which part of the satellite earth stationit is required. Explain clearly. [8]

(b) In what way a satellite earth station is different from a microwave link? Ex-plain clearly? [8]

8. Analyse various noises disturbing the received signal from satellite at earth station.

[16]

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1. Mention some important milestones in the development of satellite communicationand describe its growth. [16]

2. Describe the salient features of Direct Broadcast Satellite system with neat sketches.[16]



4. Why lens antennas are preferred for satellite communication, explain in detail.Explain the function of lens antenna. [16]

5. (a) What is the necessity of keeping front end of the satellite receiver at the

earth station in a helium-coolent: what is the range of temperature of thepreamplifier. [6]


[10]

6. Explain the Frequency Division Multiple Access of Satellite System with one ex-

ample. [16]

7. (a) A 14/11 GHz antenna has a G/T ratio of 40.3dB at 11.2 GHz. The antennagain is 64dB and the system noise temperature at 10 deg elevation anglein clear air conditions is 234k. The antenna aperture efficiency and noisetemperature are detailed in the list below. During heavy rain, the slant pathattenuation reaches 8dB for 0.01 percent of the year. Calculate G/T ratiofor their fraction of the year and the corresponding reduction in C/N for thereceived 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]

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8. (a) Draw the simplified diagram of large Earth station equipment using FDM/FM/FDMAtechnology and explain each block in detail. [10]

(b) Explain the functions of major RF components used in the above Earth stationdesign. [6]

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07 Rr410406 Satellite Communications