Results of ground-based observations of the field structure in the range of very low frequencies with a strong modification of the ionosphere by a modulated short-wave radiation

The results of ground-based observations of ELF/VLF emissions during heating experiments have been described. It has been shown that the polarization of the horizontal magnetic field is determined by the propagation conditions in the Earth - ionosphere waveguide. The polarization is linear at 1 017 Hz, predominantly linear at 3 017 Hz, and left-handed elliptical at 2 017 Hz. At the frequency of 1 017 Hz waves propagate in the TEM mode only, but at the frequency of 3 017 Hz waves propagate in three modes: TEM, TM01, TE01. A phase velocity at the frequency of 1 017 Hz has been estimated by the measured phase differences of wavefields recorded in spatially separated points