Punjab Technical University 2008 Bachelor of Fisheries Science (B.F.Sc.) SATELLITE
Sunday, 14 April 2013 12:40Web
Page 2 of 2
ans any 5 ques. out of 8 ques..
every ques. carries 16 marks.
Q.2 a. Why satellites are considered as a good place to locate a repeater? Signals reaching a satellite from an earth station and signals received on earth stations from a satellite are always very weak, why is it so? Starting from basic principles, deduce the formula for the period of the satellites orbit, T, if the orbit is circular. (12)
b. A satellite is in an elliptical orbit with a perigee of 1000 km and an apogee of 4000 km. If the mean earth radius is 6378.14 km, obtain the eccentricity of the orbit. (4)
Q.3 a. It is stated that, “ weight is the most critical factor in the design of any satellite”, provide your comments. Which are the other factors that influence the link design? Mention 3 important features of DBS-TV satellites. Derive necessary equations, that demonstrates how the CNR in the home DBS-TV receiver deteriorates when rain is in the path ranging from the satellite and the receiving antenna. (13)
b. A satellite at a distance of 40000 km from a point on earth’s surface radiates a power of 10 W from an antenna with a gain of 17 dB in the direction of the observer. compute the flux density at the receiving point in decibels. (3)
Q.4 a. List the impairments (propagation) introduced, when a signal travelling ranging from an earth station and a satellite pass through the earth’s atmosphere including the ionosphere. Mention also the physical reason for the stated impairment. (14)
b. Illustrate by a sketch the various layers in the earth’s atmosphere. (2)
Q.5 a. What is the kind of modulation used in analog satellite systems? Support your ans with proper reasoning. What is the disadvantage of the method commonly used? What is the meaning of “unweighted S/N improvement” for the modulation method used? (6)
b. Write a note on SCPC FM links. (5)
c. A baseband signal of maximum frequency equal to 3.4 KHz is used in a SCPC-FM satellite link. A subjective improvement in baseband SNR of seven dB is given by de-emphasis. If the CNR of the receiver is 13 dB, compute the baseband SNR ratio for the voice channel. If the FM demodulator has 1 FM threshold at six dB, estimate the link margin for this system. Take the RF channel bandwidth of the link as 45 KHz. (5)
Q.6 a. What is a transponder? Briefly discuss the subsequent units of a transponder:
(i) The wideband receiver.
(ii) The input de-multiplexer.
(iii) Power amplifier.
(iv) Antenna Subsystem. (14)
b. For a typical C-band communications satellite, how many transponders can be accommodated? (2)
Q.7 a. What is ‘Multiple Access’? elaborate the factors influenced by the multiple access technique? Which multiple access technique is widely used as a method of sharing the bandwidth of satellite transponders? What do you mean by pre-assigned access? (7)
b. A C-band transponder has an output spectrum for downlink signals in the frequency range 3705-3741 MHz. If the transponder carries 2 un-modulated carriers at 3718 and 3728 MHz with equal magnitudes at the input to the HPA, calculate the third-order inter-modulation products in the output of the HPA. (4)
c. For what kind of signals, is the TDMA technique best suited? Justify your ans. What is satellite-switched TDMA? (5)
Q.8 a. provide the meaning of the following:
(i) fault control. (ii) Half rate FEC. (4)
b. State Shannon-Hartley legal regulations and illustrate the ratio of plotted against in decibels for the case when H
c. With a neat sketch for illustration, briefly discuss a rate 1/2 convolutional encoder. (6)
Q.9 a. What the acronym VSAT stand for? What is the underlying concept behind most VSAT systems? With a neat schematic, briefly discuss the mode of a satellite in the BSS. (8 )
b. Briefly discuss about the option of the multiple access scheme and Access Control that concerns VSAT systems design. (8 )
| Earning: Approval pending. |
