TRUE/FALSE
1. Communications satellites could be just passive reflectors.
ANS: T
2. A typical communications satellite can cover half of the earth's surface.
ANS: F
3. Most communications satellites are in a geosynchronous orbit.
ANS: T
4. Most communications satellites are in a geostationary orbit.
ANS: T
5. "Geostationary" means the same thing as "geosynchronous".
ANS: F
6. A geosynchronous orbit is about 3,600 km above the equator.
ANS: F
7. Signals from satellites in a geosynchronous orbit suffer a great deal of free-space attenuation.
ANS: T
8. It is easier to reach a geosynchronous satellite from higher northern latitudes.
ANS: F
9. At the frequencies satellites use, the ionosphere has negligible effect.
ANS: T
10. The closer a satellite is to earth, the faster the velocity it needs to stay in orbit.
ANS: T
11. In the Northern Hemisphere, an antenna must face south to reach a satellite.
ANS: T
12. You cannot communicate with a geosynchronous satellite from the Southern Hemisphere.
ANS: F
13. You cannot communicate with a geosynchronous satellite from the South Pole.
ANS: T
14. Typically, ground antennas must be movable to "track" a geosynchronous satellite.
ANS: F
15. The azimuth and elevation needed for an antenna to "see" a certain satellite depend on the location of the antenna on the ground.
ANS: T
16. The power in the uplink signal to a typical communications satellite is in the range of 50 to 240 watts.
ANS: F
17. The power in the downlink signal from a typical communications satellite is in the range of 10 to 250 watts per transponder.
ANS: T
18. The EIRP of a satellite depends on the gain of its antenna.
ANS: T
19. The EIRP of a satellite is the same anywhere reception is possible.
ANS: F
20. It takes over half a second for a signal to go from point A to point B and back again via geostationary satellite.
ANS: T
21. The useful life of a communications satellite is over when it runs out of fuel.
ANS: T
22. The maximum useful life of a communications satellite is about three years.
ANS: F
23. Using the C band for satellites may conflict with terrestrial microwave communications.
ANS: T
24. Ku-band antennas can be smaller than C-band antennas.
ANS: T
25. Conventional analog satellite transponders cannot be used with digital data signals.
ANS: F
26. It is possible to transmit signals from one satellite to another.
ANS: T
27. In practice, the beamwidth of a parabolic reflector is independent of its diameter.
ANS: F
28. Communications satellites are particularly well suited to long-distance telephony.
ANS: F
29. With TDMA, more than one hundred earth stations can use the same satellite transponder.
ANS: T
30. LEO communications satellite systems have been a great commercial success.
ANS: F
MULTIPLE CHOICE
1. The height of the geosynchronous orbit above the equator is about:
| a. | 3,578 km | c. | 357,800 km |
| b. | 35,780 km | d. | depends on satellite velocity |
ANS: B
2. The high and low points of a satellite's orbit are called, respectively,:
| a. | apogee and perigee | c. | uplink and downlink |
| b. | perigee and apogee | d. | downlink and uplink |
ANS: A
3. The area on the earth that is "covered" by a satellite is called its:
| a. | earth station | c. | footprint |
| b. | downlink | d. | plate |
ANS: C
4. The velocity required to stay in orbit:
| a. | is constant |
| b. | is zero (freefall) |
| c. | is lower close to the earth than far from the earth |
| d. | is higher close to the earth than far from the earth |
ANS: D
5. An antenna is aimed by adjusting the two "look angles" called:
| a. | azimuth and elevation | c. | declination and elevation |
| b. | azimuth and declination | d. | apogee and perigee |
ANS: A
6. The power per transponder of a typical Ku-band satellite is in the range:
| a. | 5 to 25 watts | c. | 500 to 2500 watts |
| b. | 50 to 250 watts | d. | depends on its orbit |
ANS: B
7. The power level for an earth station to transmit to a satellite is on the order of:
| a. | 101 watts | c. | 103 watts |
| b. | 102 watts | d. | 104 watts |
ANS: C
8. The "payload" on a communications satellite consists of:
| a. | transponders | c. | solar cells |
| b. | batteries | d. | all of the above |
ANS: A
9. "Station-keeping" refers to:
| a. | antenna maintenance | c. | orbital adjustments |
| b. | power-level adjustments | d. | none of the above |
ANS: C
10. DBS stands for:
| a. | decibels of signal | c. | direct-broadcast system |
| b. | down-beam signal | d. | direct-broadcast satellite |
ANS: D
11. LNA stands for:
| a. | low-noise amplifier | c. | low-noise amplitude |
| b. | low north angle | d. | low-noise array |
ANS: A
12. A reduction in TWT power for linearity is called:
| a. | backdown | c. | power-down |
| b. | backoff | d. | EIRP drop |
ANS: B
13. TVRO stands for:
| a. | television receive only | c. | television remote origin |
| b. | television repeater only | d. | none of the above |
ANS: A
14. TDMA stands for:
| a. | transponder-directed multiple antennas | c. | time-division multiple access |
| b. | television distribution master antenna | d. | transmit delay minimum aperture |
ANS: C
15. VSAT stands for:
| a. | video satellite | c. | very small antenna terminal |
| b. | video signal antenna terminal | d. | very small aperture terminal |
ANS: D
16. On the uplink from a terminal, a VSAT system uses:
| a. | high power to a small antenna | c. | low power to a large antenna |
| b. | low power to a small antenna | d. | LEO satellites |
ANS: B
17. A typical VSAT system is configured as a:
| a. | star | c. | ring |
| b. | mesh | d. | repeater |
ANS: A
18. LEO stands for:
| a. | long elliptic orbit | c. | lateral earth orbit |
| b. | low-earth orbit | d. | longitudinal earth orbit |
ANS: B
19. For real-time communication, LEO systems require:
| a. | a constellation of satellites | c. | very high power |
| b. | tracking dish antennas | d. | all of the above |
ANS: A
20. The frequency bands used by Ku-band satellites are:
| a. | 4 GHz and 6 GHz | c. | 20 GHz and 30 GHz |
| b. | 12 GHz and 14 GHz | d. | none of the above |
ANS: B
COMPLETION
1. A satellite in geosynchronous orbit takes ____________________ hours to complete one orbit.
ANS: 24
2. The ____________________ is the signal path from the earth station to the satellite.
ANS: uplink
3. The ____________________ is the signal path from the satellite to the earth station.
ANS: downlink
4. A satellite in a ____________________ orbit appears to stay directly above one spot on the equator.
ANS: geostationary
5. Non-geostationary satellites are sometimes called ____________________ satellites.
ANS: orbital
6. A geosynchronous orbit is about ____________________ km above the earth.
ANS: 35,780
7. A ____________________ is an outline of the area on the earth's surface that a satellite broadcasts to.
ANS: footprint
8. All satellite orbits are ____________________ in shape.
ANS: elliptical
9. The ____________________ is the distance of a satellite's closest approach to the earth.
ANS: perigee
10. The ____________________ is a satellite's farthest distance from the earth.
ANS: apogee
11. An antenna's ____________________ is its angular direction between east and west.
ANS: azimuth
12. An antenna's ____________________ is its vertical angle with respect to the earth's surface.
ANS: elevation
13. An antenna's ____________________ is the angle by which it is offset from the earth's axis.
ANS: declination
14. Satellites using the ____________________ band operate on 12 GHz.
ANS: Ku
15. The time for a signal to make a round trip via satellite is about ____________________ milliseconds.
ANS: 500
16. A ____________________ is a type of repeater used on communications satellites.
ANS: transponder
17. Both the gain and the beamwidth of a dish antenna depend on its ____________________.
ANS: diameter
18. VSAT systems commonly use a ____________________ network configuration.
ANS: star
19. To date, LEO satellite systems have been a financial ____________________.
ANS: failure
20. C-band antennas are ____________________ than Ku-band antennas.
ANS: larger
SHORT ANSWER
1. A receiving antenna with a gain of 44.4 dBi looks at a sky with a noise temperature of 15 K. The loss between the output of the antenna and the input of the LNA is 0.4 dB, and the LNA has a noise temperature of 40 K. Calculate the G/T.
ANS:
25 dB
2. A receiver has a noise figure of 1.7 dB. Find its equivalent noise temperature.
ANS:
139 K.
3. A receiving antenna with a G/T of 25 dB is used to receive signals from a satellite 38,000 km away. The satellite has a 100-watt transmitter and an antenna with a gain of 30 dBi. The signal has a bandwidth of 1 MHz at a frequency of 12 GHz. Calculate the C/N at the receiver.
ANS:
38 dB
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