Modern high-efficiency EER transmitters to comply with the standards for electromagnetic compatibility require very precise matching with the load. The antennas used on board are often electrically short and therefore narrow-banded. Traditional LC-matching in some cases can not provide the required level of SWR. A method for matching electrically short narrow-band antennas with the help of RLC-circuits is proposed. It allows providing the required SWR value of the load not more than 1.05 in the band of the OFDM signal of 10 kHz and not more than 1.1 in the band of 20 kHz. A technique for designing a RLC frequency extension circuit is developed. The carried out analysis of the energy efficiency of the frequency extension circuit showed that if the antenna 3-dB bandwidth exceeds 10 kHz, the losses in the FEC do not exceed 1 dB. The developed method for calculating the frequency extension circuit was tested for Digital Radio Mondiale (DRM) LW broadcasting stations. The possibility matching of existing antennas with a height of 257 meters for the DRM mode with 9/10 kHz signal bandwidth over the entire range of LW is shown. Also, the potential for using Simulcast mode with a dual signal bandwidth is shown: for the upper half of the low-frequency range, with antennas 257 meters high and 378 meters for the lower one.