We present the results of first studies of the modification of the ionosphere by high-power HF radiation, which were obtained using signals of high-orbit GPS/GLONASS navigation satellites. Enhancement of the ionospheric modification in the magnetic-field direction was observed for the first time. This leads to a total decrease in electron number density and the formation of electron density irregularities near the magnetic-zenith direction. The efficiency of using GSP/GLONASS satellite signals for the studies of the ionosphere modified by HF radiation is demonstrated. Prospects for further studies in this field are discussed.

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