(a)[2]
State two reasons why frequencies in the gigahertz (GHz) range are used for satellite communication.
(b)[2]
In one satellite communication system, the frequency of the signal sent from Earth to the satellite (the up-link) is $6\,\text{GHz}$. The frequency of the signal sent back to Earth from the satellite (the down-link) is $4\,\text{GHz}$. Explain why the two signals are transmitted at different frequencies.
(c)[3]
A signal sent from Earth has a power of $3.1\,\text{kW}$. By the time it is received by a satellite, this signal has suffered an attenuation of $185\,\text{dB}$. Calculate the power of the signal received by the satellite.