This page has various ITU-R SG3 model implementations
The P.619 Model is used to predict loss between ground and satellite stations which includes the basic transmission loss as well as the beam spreading and atmospheric gas loss.
Basic transmission loss for single-entry interference
P.619 - Section 3.3
The clear-air basic transmission loss not exceeded for 𝑝% time for a single unwanted transmitter and victim receiver over an Earth-space path..
Prediction of beam Spreading and Atmospheric Gas Losses
P.619 - Section x.2
The clear-air basic transmission loss not exceeded for 𝑝% time for a single unwanted transmitter and victim receiver over an Earth-space path..
