A model of a satellite communication system based on wideband signals with relative diphase encoding is developed in the paper. A system of four signals with binary phase shift keying is used. Spectra of the signals are spread by the direct sequence technique. The developed system operation under conditions of impulse electromagnetic interference and under the influence of fluctuation interference is simulated. The dependences of bit error rate on signal-to-interference ratio are evaluated in the cases of impulse interference with Johnson distribution and white Gaussian noise affecting the signal.