The Link-Power Budget Equation:
Now that the losses for the link have been identified, the power at the receiver, which is the power output of the link, may be calculated simply as [EIRP] [LOSSES] [GR], where the last quantity is the receiver antenna gain.
Note carefully that decibel addition must be used.
The major source of loss in any ground-satellite link is the free-space spreading loss [FSL], the basic link-power budget equation taking into account this loss only. However, the other losses also must be taken into account, and these are simply added to [FSL]. The losses for clear-sky conditions are
[LOSSES] = [FSL] + [RFL] + [AML] + [AA] - [PL] equation for the received power is then
[PR] = [EIRP] x [GR] - [LOSSES]
where [PR] received power, dBW
[EIRP] --> equivalent isotropic radiated power, dBW [FSL] free-space spreading loss, dB
[RFL] --> receiver feeder loss, dB
[AML] --> antenna misalignment loss, dB
[AA] --> atmospheric absorption loss, dB [PL] polarization mismatch loss, dB