Implementation of amplitude modulation companding in the BBC MF national networks

The design and development of a modulation-controlled system known as amplitude modulation companding (AMC) is described. In this method both carrier and sideband levels are progressively reduced as the modulation level is increased, this effect being compensated in the receiver by the normal action of the automatic gain control circuit. Extensive trials of a fully developed system for 50-kW MW transmitters have achieved input power savings of between 20% and 40%, depending on program content. This is achieved with imperceptible loss of coverage, and further savings may be possible