|There are two main sources of noise in a satellite system:
- Noise arising in the satellite and earth-station equipment, and
- Noise collected by the satellite and earth-station antennas
The antenna receives noise from the sky and from the earth.
Sky noise comprises cosmic (galactic) noise and noise resulting from absorption and
re-radiation of energy by water and oxygen molecules in the atmosphere
Noise power radiated by the Earth is collected by the sidelobes of the earth-station
antenna and the main beam of the satellite antenna.
Noise power N is related to an equivalent noise temperature by the expression:
N = k . T . B watts
K is Boltzmann's constant (1.38 x 10-23 J/K)
B is the bandwidth in which the noise is measured (in Hz)