Subject and Purpose. Considerable attention has traditionally been given to the interaction of high-power radio-frequency emissions with the ionosphere. The great many physical effects taking place within the limits of a powerful (heating) facility’s antenna pattern are subjected here to a thorough and detailed analysis. Also, the application of high-power radio emissions provides a convenient means for studying subsystem coupling in the Earth-atmosphere-ionosphere-magnetosphere system, as well as of generation and propagation of disturbances well beyond the antenna pattern of the transmitter. The present paper has been aimed at analyzing the features revealed by the large-scale ionospheric disturbances as these are generated under the impact of either monopulse or periodic radio-frequency emissions from an HF heating facility. Methods and Methodology. In the course of the experiments, the ionosphere was affected with high power radio frequency emission from the heating facility Sura. The disturbances were diagnosed at a distance of 960 km from the heater, with the aid of a vertical incidence Doppler radar. Results. It has been found that through the period of minimal solar activity the ionospheric disturbances observable at a range about 103 km from the heater did arise as the effective radiated power of the latter approached to 25 MW. The duration of the ionospheric response to the impact of an incident monopulse was equal to the length of that latter, while the quasi-periodic variations shown by the Doppler frequency shift just started to appear. The apparent horizontal speed of the propagating disturbances was found to vary from about 300 m/s to 420 m/s. Note that speed to increase at higher altitudes. The periodic mode of heater operation was accompanied by generation of quasi-periodic disturbances in the electron density, of relative amplitudes about 1% and periods close to the Brunt–Väisälä period. Conclusions. The basic features of Doppler spectrum variations, contained in the signals from a diagnostic radar, have been identified in connection with high-power HF radiation incident on the ionosphere
