Theoretical estimate of average power of narrowband intersystem interferences in a free space

The paper describes calculated ratios to determine a power of intersystem interference from located in a random way narrowband sources in a specified zone of a free space. Theoretical calculation results differ from results of modelling by statistical tests by less than 2%. It has been shown that total power of intersystem interferences from in-phase sources in the low frequency range varies directly as quantity of the sources by square law.