25483999 Ec 1015 Satellite Communication r2004 May June 09 Be t

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B.E/B.Tech. DEGREE EXAMINATION, MAY/JUNE 2009

Eighth Semester

Electronics and Communication Engineering

EC 1015 --- SATELLITE COMMUNICATION

(Common to VII Semester B.Tech. Information Technology and

VII Semester Part-Time B.E (ECE))

(Regulation 2004)

Time : Three hours Maximum: 100 Marks

Answer ALL questions

PART A (10 x 2=20 Marks)

1. A satellite is orbiting in the equatorial plane with a period from perigee to perigee of

12 hours. Given that the eccentricity is 0.002, calculate the semi-major axis. The

earth's equatorial radius is 6378.1414 km.

2. What are polar orbiting satellites?

3. Determine the angle of tilt required for a polar mount used with an earth station at

latitude 49° north. Assume a spherical earth of mean radius 6371 km and ignore

earth station altitude.

4. What is a transponder?

5. A satellite downlink at 12 Ghz operates with a transmit power of 6W and an antenna

gain of 48.2 dB. Calclulate the ERIP in dBW.

6. What is intermodulation noise?

7. What is a SPADE system?

8. What is CDMA?

9. What is the orbital spacing of a satellite?

10.What are VSATs?



PART B – (5 x 16 = 80 Marks)

11. (a) (i) State Kepler's three laws of planetary motion. Explain their relevance to

artificial satellites orbiting the earth. (8)

(ii) Define Universal time and sideral time. (4)

(iii) The cosmos 1675 satellite has an apogee height of 39342 km and a perigee

hight of 613 km. Determine the semimajor axis and the eccentricity of its

orbit. Assume a mean earth radius of 6371 km. (4)

OR

(b) (i) Discuss about frequency allocations for satellite services. (8)

(ii) What are the effects of a non spherical earth on the orbital mechanics of

a satellite? (4)

(iii) Calculate the radius of a circular orbit for which the period is 1 day. (4)

12. (a) (i) Discuss about near Geostationary orbits. (6)

(ii) Determine the limits of visibility for an earth station situated at mean sealevel, at latitude 48.42° north and longitude 89.26° west. Assume a minimum

angle of elevation of 5°. (6)

(iii) Discuss abou sun transit outage. (4)

OR

(b) (i) Discuss in detail about attitude control of a satellite. (8)

(ii) What is the chief advantage of TWTA used aboard satellites compared to

other types of high power amplifiers? What are the main disadvantages of

TWTA? (4)

(iii) What is thermal control? Why is it required? (4)

13. (a) (i) With the aid of a block diagram, describe the functioning of the indoor

receiving unit of a satellite TV/FM receiving system intended for homereception. (8)



(ii) In most satllite TV receivers, the first IF band is converted to a second, fixed

IF. Why is this second frequency conversion required? (2)

(iii) Discuss about antenna misalignment losses with relevant figures. (6)

OR

(b) (i) An antenna has a noise temperature of 35 K and is matched into a receiver

which has a noise temperatur eof 100 K. Calculate the noise power density

and the noise power bandwidth of 36 MHz. (4)

(ii) What is input backoff? Describe it. Also substantiate the reason behind

employing it. (6)

(iii) Derieve the link power budget equation. (6)

14. (a) (i) Discuss in detail about direct sequence spread spectrum. (8)

(ii) In a TDMA network the reference burst and the preamble each requires 560

bits and the nominal guard interval between bursts is equivalent to 120 bits.

Given that there are eight trafffic bursts and one reference burst per frame and

the total frame length is equivalent to 40800 bits, calculate the frame

efficiency. (4)

(iii) Distinguish between preassigned and demand assigned traffic in relation to a

satellite communication network. (4)

OR

(b) (i) Discuss in detail about satellite links and TCP. (10)

(ii) Explain what is meant by asymmetric channels. Describe how asymmetricchannels may be incorporated in internet connections via satellites. (6)

15. (a) (i) For a 24 Mhz bandwidth transponder and allowing for a roll off factor of 0.2,

what is the symbol rate? (2)

(ii) Discuss in detail about MPEG compression standards. (10)

(iii) The EIRP of a 240 W transponder is 57 dBW. Calculate the approximate gain

of the antenna. Suppose if this transponder is switched to 120 W. What will bethe new EIRP, given the same antenna is used? (4)



OR

(b) (i) Discuss in detail about Global Positioning satellite system. (10)

(ii) Write brief notes on the advantages and disadvantages of using satellites in

LEOs, MEOs and GEOs for mobile satellite communications. (6)

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25483999 Ec 1015 Satellite Communication r2004 May June 09 Be t