This is the Coaching materials in Satellite Communications Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Satellite Communications Coaching Materials Part 1
1. What are the two types of communications satellite
Passive and active
2. A typical satellite communications operational link consists of a satellite and what other two components?
Earth terminals
3. What areas of the earth are not normally covered by satellites?
Extreme polar regions
4. Satellite orientation in space is important for what two reasons?
To allow maximum solar exposure to the sun and satellite antenna exposure to earth terminals
5. What types of antennas are generally used at earth terminals?
Large, high-gain parabolic antennas
6. Why do earth terminals require highly sensitive receivers?
To overcome satellite transmitter low power and permit extraction of the desired information from the received signal
7. Why is satellite acquisition and tracking important?
To ensure earth terminal antennas are always pointed towards the satellite
8. What are the two limitations to an active satellite communications system?
Satellite down-link transmitter and up-link receiver sensitivity
9. If the line-of-sight distance for an optical beam is 12 km, what would is be, approximately, for a microwave beam?
16 km
10. The power in the downlink signal from a typical communications satellite is in the range of _____ per transponder.
10 to 250 watts
11. The power level for an earth station to transmit to a satellite is in the order of:
10^3 watts
12. Ku-band antennas can be _____ than C-band antennas.
Smaller
13. A geosynchronous orbit is about _____ km above the earth.
35,780
14. A Global Positioning System (GPS) or NAVSTAR is
MEO
15. GPS or NAVSTAR height is
9500 miles
16. An antenna’s angular direction between east and west?
Azimuth
17. An antenna’s vertical angle with respect to the earth’s surface.
Elevation
18. An antenna’s angle by which it is offset from the earth’s axis
Declination
19. In geostationary satellites, “station-keeping” means:
Adjusting the orbits
20. A reduction of TWT power for linearity is called:
Backoff
21. The frequency bands used by Ku-band satellites are:
12 GHz and 14 GHz
22. Satellite operating at 27 – 30 GHz
Ka-band
23. The law that states that a satellite will orbit a primary body following an elliptical path.
1st Law of Kepler
24. Kepler’s 2nd law is known as
Law of areas
25. Kepler’s 3rd law is also known as
Harmonic law
26. Low Earth Orbit (LEO) satellite orbits around the earth at a height of
370 miles
27. Medium Earth Orbit (MEO) satellite orbits around the earth at a height approximately _____.
6000 miles to 12,000 miles
28. Geosynchronous satellites are high-altitude earth-orbit satellites with heights about _____.
22,300 miles or 36,000 km
29. Iridium is a LEOSAT that has a height of approximately
480 miles
30. MEO frequency band is
1.2 -1.66 GHz
31. All satellites rotate around the earth in an orbit that forms a plane that passes through the center of gravity of earth called
Geocenter
32. The point on the surface of the earth directly below the satellite
Subsatellite point (SSP)
33. The minimum acceptance angle of elevation
5 degrees
34. The spatial separation of a satellite is between _____.
3 degrees to 6 degrees
35. Antenna used with a rotating satellite whose main beam is continuously adjusted so that it will illuminate a given area on the earth’s surface
Despun
36. Satellite’s radiation pattern that typically target up to 20% of the Earth’s surface
Hemispherical beams
37. The radiation pattern that has a satellite’s antenna beamwidth of 17 degrees and are capable of covering approximately 42% of the earth’s surface
Earth or global beams
38. Geostats has an earth coverage of approximately
42.5%
39. LNA stands for:
Low-noise amplifier
40. LNA in satellite transponder system commonly used
Tunnel
41. Find the velocity of a satellite in a circular orbit (a) 500 km above the earth’s surface (b) 36,000 km above the earth’s surface (approximately the height of geosynchronous satellite).
(a) 7.6 km/s (b) 3.07 km/s
42. Calculate the angle of declination for an antenna using a polar mount at latitude of 45 degrees.
6.81 degrees
43. Calculate the length of the path to a geosynchronous satellite from an earth station where the angle of elevation is 30 degrees.
39 x 10^3 km
44. A satellite transmitter operates at a 4 GHz with a transmitter power of 7W and an antenna gain of 40 dBi. The receiver has antenna gain of 30 dBi and the path length is 40,000 km. Calculate the signal strength at the receiver.
-88 dBm
45. A receiving antenna with a gain of 40 dBi looks at at a sky with a noise temperature of 15K. The loss between the antenna and the LNA input, due to the feedhorn, is 0.4 dB, and the LNA has a noise temperature of 40K. Calculate G/T (Antenna gain-to-noise-temperature).
20.6 dB
46. A receiver has a noise figure of 1.5 dB. Find its equivalent noise temperature.
119K
47. The receiving installation whose G/T was found to be 20.6 dB is used as a ground terminal to receive a signal from a satellite at a distance of 38,000 km. the satellite has transmitter power of 50 watts and an antenna gain of 30 dBi. Assume losses between the satellite transmitter and its antenna is negligible. The frequency is 12 GHz. Calculate the carrier-to-noise ratio at the receiver, for a bandwidth of 1 MHz.
30.6 dB
48. If a satellite has a total transmitter power (Pt) of 1000 W, determine the energy per bit (Eb) for a transmission rate of 50 Mbps.
-47 dBW/bps or -47 dbJ
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49. For an equivalent noise bandwidth of 10 MHz and a total noise power of 0.00276 pW, determine the noise density and equivalent noise temperature.
276 x 10^-23 W/Hz or -205.6 dBW/Hz
50. A typical TVRO installation for use with C-band satellite (downlink at approximately 4 GHz) has a diameter of about 3 m and an efficiency of about 55%. Calculate its gain and beamwidth.
G = 39 dB, beamwidth = 1.75 degrees
51. For an earth station transmitter with an antenna output power of 40dB (10000 W), a back-off loss of 3dB, a total branching and feeder loss of 3dB, and a transmitter antenna gain of 40dB, determine the EIRP
74 dBW
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