SUMMARY
Established that, directivity diagram of the system of “basic antenna – fuselage of helicopter” becomes a function of the time due to the presence of the metal main screw, which during rotation, periodically changes geometry of aircraft body. In this case the radio signal, which is received or radiated by helicopter antenna system undergoes undesirable parametric transformations. The mathematical model of parametric transformational system is proposed which is the base for investigation of spectral composition of distorted signals with amplitude and angle modulation. The recieved results are analyzed and summarized