Deemed University 2009 A.M.I.E.T.E Electronics

Q.3 a. Distinguish ranging from atmospheric attenuation and atmospheric absorption and write a brief note on atmospheric absorption loss. (6)

b. In the study of an earth station receiver, to determine its performance, which is the important volume that the designer is needed to evaluate? Briefly comment on the above volume. Write the block diagram of an earth station receiver with single frequency conversion. (7)

c. An LNA is connected to a receiver which has a noise figure of 12 dB. The gain of the LNA is 40 dB, and its noise temperature is 120K. What is the overall noise temperature referred to the LNA input? (3)

Q.4 a. elaborate the objectives in the design of any satellite communication? What do you mean by a link budget? How does it help the designer? (7)

b. A DBS-TV system has the following:
(i) Noise temperature of LNA=110 K
(ii) Antenna noise temperature in clear sky condition = 12 K
(iii) Clear sky system noise temperature = 145 K
(iv) Down-link (C/N) ratio in clear sky conditions = 14.3
(v) Sky noise temperature in rain = 147 K.

compute the increase in noise power, caused by the increase in the sky noise temperature due to rain and the resulting value, when rain intersects the down link. Take the rain attenuation in the downlink as 3-dB. (9)

Q.5 a. Why PSK is preferred in satellite links that FSK? Write the general expression for the baseband S-N-R of a satellite system that uses FM. describe the term deviation ratio for FM. (6)

b. Distinguish ranging from TDM and FDM. Write 6 important points that 1 should know of a TDM system in general. Illustrate the slot organisation of 1 T1 frame for the US.T1 TDM system (10)

Q.6 a. What is a transponder? What is the typical bandwidth of a transponder and how many transponders can be accommodated in the bandwidth allocated for C-band service? (7)

b. What is the function of antennas carried aboard a satellite? Write the equations for the gain and the –3 dB beamwidth for a paraboloidal reflector and comment on the key factor in the above equations. (9)

Q.7 a. Distinguish ranging from multiple access and multiplexing. What do you mean by a TDM-TDMA signal? With necessary illustrations, briefly define a typical fixed assignment FDMA plan for 2 C-band transponders. (6)

b. 3 identical large earth stations with 500 W saturated output power transmitters access a 36 MHz bandwidth transponder using FDMA. The saturated output power of the transponder is 40 W and it is operated with 3-dB output backoff when FDMA is used. The bandwidths of the earth station signals are : Station one = 15MHz, Station two = 10MHz, Station three = 5MHz. obtain the transponder output power allocated to every earth stations signal. (10)

Q.8 a. What is the function of the CDMA chip sequence? CDMA is also known as spread spectrum, why is it so? What do you mean by low probability of intercept? Is CDMA widely adopted by satellite communication systems? Support your ans with relevant reasoning. (7)

b. What is the underlying concept behind most VSAT systems? What is spoofing? elaborate the major elements that concern VSAT systems design? elaborate the factors that often determine the option ranging from FDMA, TDMA & CDMA for VSAT networks? describe outbound or outroute channel for an FDMA VSAT system. (9)

Q.9 a. Write the formula that defines the upper limit on the info capacity of the channel for any digital communication system that operates with a noisy channel. (4)

b. Write the general form of a linear block codeword. What does fault control perform? Why are cyclic codes widely used in satellite transmission? Write a note on Golay codes. (9)

c. How are convolutional codes generated? describe the term state of a convolution encoder. (3)

Earning:   Approval pending.