Both the reduction of spectrum width of a s.s,b. transmission and its lower spectrum pollution, due to the absence or diminution of a carrier component, make this mode of modulation attractive for future use in land mobile radio. Outstanding problems are frequency stabilityand a.g.c. The latter cannot be of the ‘hang’ type used at h.f. In the Wolfson system a low amplitude audio tone transmitted at the centre of the audio pass-band is used for both a.g.c. and a.f.c. A hierarchy of receivers, from simple, manually clarified to sophisticated, fully automatic types, is described, to meet the needs of varied users. The proposed systemappears to have several advantages over other contenders