Tuesday, December 8, 2009

Eigth Semester
(Regulation 2004)
Electronics and Communication Engineering
(Common to VII Semester B.Tech. Information Technology and VII Semester Part-Time B.E. (ECE))
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 degrees 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 6 W and an antenna gain of 48.2 dB. Calculate the EIRP in dBW.

6. What is intermodulation noise?

7. What is a SPADE system?

8. What is CDMA?

9. What is the orbital spacing of satellites?

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. [Marks 8]

(ii) Define Universal time and sidereal time. [Marks 4]

(iii) The cosmos 1675 satellite has an apogee height of 39342 Km and a Perigee height of 613 Km. Determine the semimajor axis and the eccentricity of its orbit. Assume a mean earth radius of 6371 Km. [Marks 4]


11.(b)(i) Discuss about frequency allocations for satellite services. [Marks 8]

(ii) What are the effects of a nonspherical earth on the orbital mechanics of a satellite? [Marks 4]

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

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

(ii) Determine the limits of visibility for an earth station situated at mean sea level, at latitude 48.42 degrees north and longitude 89.26 degrees West. Assume a minimum angle of elevation of 5 degrees. [Marks 6]

(iii) Discuss about sun transit outage. [Marks 4]


12.(b)(i) Discuss in detail about attitude control of a satellite. [Marks 8]

(ii) What is the chief advantage of the TWTA used aboard satellites compared to other types of high power amplifiers? What are the main disadvantages of TWTA? [Marks 4]

(iii) What is thermal control? Why is it required? [Marks 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 home reception. [Marks 8]

(ii) In most satellites TV receivers, the first IF band is converted to a second, fixed IF. Why is this second frequency conversion required? [Marks 2]

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


13.(b)(i) An antenna has a noise temperature of 35 K and is matched into a receiver which has a noise temperature of 100 K. Calculate the noise power density and the noise power for a bandwidth of 36 MHz. [Marks 4]

(ii) What is input backoff? Describe it. Also substantiate the reason behind employing it. [Marks 6]

(iii) Derive the link power budget equation. [Marks 6]

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

(ii) In a TDMA network the reference burst and the preamble each requires 560 bits and the nominal guard interval between burats is equivalent to 120 bits.Given that there are eight traffic bursts and one reference burst per frame and the total frame length is equivalent to 40800 bits, Calculate the frame efficiency. [Marks 4]

(iii) Distinguish between preassigned and demand assigned trffic in relation to a satellite communications network. [Marks 4]


14.(b)(i) Discuss in detail about satellite links and TCP. [Marks 10]

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

15.(a)(i) For a 24 MHz bandwidth transponder and allowing for a roll off factor of 0.2, what is symbol rate? [Marks 2]

(ii) Discuss in detail about MPEG compression standards. [Marks 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 be the new EIRP, given the same antenna is used? [Marks 4]


15.(b)(i) Discuss in detail about Global Positioning satellite System. [Marks 10]

(ii) Write brief notes on the advantages and disadvantages of using satellites in LEOs, MEOs and GEOs for mobile satellite communications. [Marks 6]

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