The system gain is part of the link budget and known as Maximum Allowed Path Loss (MAPL).
A practical implementation of a link budget is described in 'How to > Link budget'
The System gain of a radio link is calculated as per the following:
T | Power of the transmitter in dBm |
L1 | Transmitter line loss in dB |
A1 | Transmitter antenna gain relative to an isotropic antenna (dBi) |
A2 | Receiver antenna gain relative to an isotropic antenna (dBi) |
L2 | Receiver line loss in dB |
R | Receiver sensitivity where the voltage is used as provided by a 0 dBd dipole antenna with a impedance of 50 ohm. |
The system gain MAPL is expressed in dB:
MAPL | System gain in dB |
MAPL = (T - L1 + A1 + A2 - L2) - R