Parameters of the developed controlled source radiomagnetotelluric (CSRMT) system are considered. A horizontal electric dipole is used as a source. It ensures measurements at a significant distance (up to 3-4 km) in a wide frequency range 1-1000 kHz. The use of relatively high frequencies is a cause to take into account displacement currents in the air. In comparison with the quasi-stationary case, there are some differences, which should be taken into account at field measurements and data interpretation. At mapping of a paleo-valley the CSRMT application permits deriving the geoelectric section which is confirmed by vertical electric sounding, reflection seismic and borehole data.