A method is presented for determining long-term reliability curves for received signal levels and combined signal levels due to diversity in a scatter communications link. The incoming signals are assumed to be faded and have a Rayleigh distribution. These reliability calculations may be made for any specific time interval or all hours. The method accounts for various orders of diversity, types of signal combining, nonlinear receiver characteristics below threshold, and median variation of the received signal. A concept and method for determining effective diversity reliability curves is also included. The effective diversity arises from the use of a squelch in a receiver located at threshold for improving SNR's.