blake_ch20.pdf

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Chapter 20: Satellite Communications

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. footprintb. 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 wattsb. 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


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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


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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.


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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


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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. Thesatellite 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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