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Satellite Communications Exam 2017

This document is an exam paper for a satellite communications course. It contains two parts: Part A has 10 short answer questions worth a total of 25 marks. The questions cover topics like elevation angle, satellite frequency bands, noise figure, antenna size calculations, multiple access techniques, and GPS signals. Part B has 5 units with 2 questions each worth a total of 50 marks. The questions require longer explanations and calculations on topics like satellite orbits, tracking and control systems, link budgets, modulation techniques, and multiple access protocols.

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66 views2 pages

Satellite Communications Exam 2017

This document is an exam paper for a satellite communications course. It contains two parts: Part A has 10 short answer questions worth a total of 25 marks. The questions cover topics like elevation angle, satellite frequency bands, noise figure, antenna size calculations, multiple access techniques, and GPS signals. Part B has 5 units with 2 questions each worth a total of 50 marks. The questions require longer explanations and calculations on topics like satellite orbits, tracking and control systems, link budgets, modulation techniques, and multiple access protocols.

Uploaded by

Murthy
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Code No: 118EK

R13
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
B. Tech IV Year II Semester Examinations, May - 2017
SATELLITE COMMUNICATIONS
(Electronics and Communication Engineering)
Time: 3 hours Max. Marks: 75
Note: This question paper contains two parts A and B.
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B
consists of 5 Units. Answer any one full question from each unit. Each question carries
10 marks and may have a, b, c as sub questions.

PART - A
(25 Marks)
1.a) Define Elevation angle and write an expression for it. [2]
b) List different bands along with frequency range for satellite communications. [3]
c) An amplifier has a quoted noise figure of 2.5 dB. What is its equivalent noise
temperature. [2]
0 0
d) A geographic area subtends an angle of approximately 6 ×3 , when viewed from
geostationary orbit. What dimension must a reflector antenna have to illuminate half of
this area with a circular beam 3o in diameter at 11 GHz. [3]
e) What is mean by multiple access? [2]
f) Compare TDMA and FDMA [3]
g) What are the different signals transmitted by GPS satellites? [2]
h) What are the features of GPS? [3]
i) List the features of pure ALOHA. [2]
j) List the features of slotted ALOHA. [3]

PART - B
(50 Marks)
2.a) Discuss the effects of sun and moon on satellite communication.
b) Illustrate geostationary transfer orbit and AKM approach to geostationary orbit using a
neat diagram. [5+5]
OR
3.a) A low earth orbit satellite is at an altitude of 250km above the earth’s surface. Assuming
earth’s diameter is approximately 12,756.28km, calculate the period of when the orbit is
circular. Also find the linear velocity of the satellite along its orbit.
b) Write short notes on solar eclipse. [5+5]

4.a) Explain the operation of a TT&C system using relevant block diagram.
b) An earth station has a diameter of 30m, has an overall efficiency of 69% and is used to
receive a signal at 4150MHz. At this frequency the system noise temperature is 79K
when the antenna points at the satellite at an elevation angle of 28o. What is the G/T
under these conditions? If heavy rain causes the rise in system noise temperature to 88K,
what is the new G/T value? [5+5]
OR

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5.a) Explain the role of a transponder in satellite communication. Also draw the simplified
diagram of a double conversion transponder for 14/11 GHz band.
b) Briefly discuss the link budget. [5+5]

6. Explain the principle of CDMA and spread spectrum transmission and reception. [10]
OR
7.a) Assume that a TDMA system uses a 125μs frame time. Find the number of channels that
each earth station can send within the TDMA frame when i) No time is lost in overheads,
preambles ii) A 5μs preamble is added at the beginning of each earth stations
transmission. iii) A 5μs delay preamble is added to each earth stations transmission and
2 μs guard band is allowed between every transmission.
b) Explain the principle of FDMA. [5+5]

8.a) Draw the block diagram of a typical earth station transmitter and explain.
b) Explain different power test methods. [5+5]
OR
9. Discuss in detail different GPS. [10]

10. Explain how message is transmitted by TDMA. [5+5]


OR
11.a) Briefly discuss the satellite packet switches.
b) Elaborate packet reservation. [5+5]

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