Purpose: To analyze the cause of quality deterioration or total lack of train hectometre-wave (HMW) radio communication (TRC) on 25 kV AC railway sections using reactive-power compensation semiconductors having pulse-modulated output parameters with changing pulse time parameters. Methods: The analysis was carried out based on the replacement circuit of the compensation device output filter where distributed elements including parasitic ones were replaced by concentrated ones, which made it possible to predict a change in the nature of the element’s reaction in the frequency domain and, consequently a change in the filter transfer characteristics. In particular, the filter characteristics changes were studied when it was connected to a railway section represented as a homogeneous artificial line. The filter’s main parasitic parameters were approximately determined according to the engineering techniques based on the geometric dimensions of the elements as such and their connections. In compliance with the requirements of regulatory standards, the filter transmission coefficient for the hectometer range frequency has been determined analytically. A set of computer models was developed in the LTSpice package that helped to study the filter frequency characteristics and their change depending on the magnitude of the elements’ parasitic parameters, as well as the filter compliance with the requirements. In particular, an analytical calculation of the filter characteristics by the method of complex amplitudes was carried out taking into account the alternating magnetization loss of the high-frequency filter choke material applied. Results: Based on the calculations carried out, the optimal filter configuration has been selected starting from a frequency of 100 kHz providing interference suppression at a level not lower than 45 dB (178 times). The filter transfer characteristics have been considered for both common-mode and differential components of the interference. The filter parameters have been selected, among other things, in such a way that there would be no good side resonances that could lead to self-excitation of the compensation device that would generate its own harmonics. Practical significance: A solution has been found to provide and possibly refine reactive-power compensation devices with smooth control based on semiconductor converters to ensure their electromagnetic compatibility in the radio frequency band.