FMX mobile reception

A general overview is presented of the FMX stereo broadcasting system that provides reduction of background and multipath noise without a loss of stereo separation. The FMX system reduces noise in stereo reception by compressing the stereo difference signal before transmission and expanding it to its original dynamic range at the receiver. The system uses the standard FM stereo composite format with the addition of a new subcarrier for the compressed signal. The added subcarrier is in quadrature with the regular stereo subcarrier at 38 kHz. The compression characteristic provides linear operation at a fixed gain of 14 dB over much of the program dynamic range, while at the highest modulation levels FMX program signals are attenuated to permit delivery of full modulation power for the existing broadcast service. Topics discussed include FMX operation under multipath conditions, multipath detection, and the dynamic equalization techniques used in FMX receivers