Page 415 - Satellite Communications, Fourth Edition

The Space Link 395

12.17. Explain why the LNA of a receiving system is placed at the antenna end
of the feeder cable.

12.18. An antenna having a noise temperature of 35 K is connected through
a feeder having 0.5-dB loss to an LNA. The LNA has a noise temperature of 90
K. Calculate the system noise temperature referred to (a) the feeder input and
(b) the LNA input.

12.19. Explain what is meant by carrier-to-noise ratio. At the input to a receiver
the received carrier power is 400 pW and the system noise temperature is 450 K.
Calculate the carrier-to-noise density ratio in dBHz. Given that the bandwidth
is 36 MHz, calculate the carrier-to-noise ratio in decibels.

12.20. Explain what is meant by the G/T ratio of a satellite receiving system. A
satellite receiving system employs a 5-m parabolic antenna operating at 12 GHz.
The antenna noise temperature is 100 K, and the receiver front-end noise
temperature is 120 K. Calculate [G/T].

12.21. In a satellite link the propagation loss is 200 dB. Margins and other
losses account for another 3 dB. The receiver [G/T] is 11 dB, and the [EIRP] is
45 dBW. Calculate the received [C/N] for a system bandwidth of 36 MHz.

12.22. Acarrier-to-noise density ratio of 90 dBHz is required at a receiver having
a [G/T] ratio of 12 dB. Given that total losses in the link amount to 196 dB,
calculate the [EIRP] required.

12.23. Explain what is meant by saturation flux density. The power received
by a 1.8-m parabolic antenna at 14 GHz is 250 pW. Calculate the power flux
2
2
density (a) in W/m and (b) in dBW/m at the antenna.
12.24. An earth station radiates an [EIRP] of 54 dBW at a frequency of 6 GHz.
Assuming that total losses amount to 200 dB, calculate the power flux density
at the satellite receiver.

12.25. A satellite transponder requires a saturation flux density of 110
2
dBW/m , operating at a frequency of 14 GHz. Calculate the earth station [EIRP]
required if total losses amount to 200 dB.
12.26. Explain what is meant by input BO. An earth station is required to
operate at an [EIRP] of 44 dBW in order to produce saturation of the satellite
transponder. If the transponder has to be operated in a 10 dB input BO mode,
calculate the new value of [EIRP] required.

12.27. Determine the carrier-to-noise density ratio at the satellite input for an
uplink, which has the following parameters: operating frequency 6 GHz,
1
2
saturation flux density 95 dBW/m , input BO 11 dB, satellite [G/T] 7 dBK ,
[RFL] 0.5 dB. (Tabulate the link budget values as shown in the text).