chapter  17
8 Pages

Frequency modulation

The problems of using AM on the medium waveband led to a different form of modulation being adopted for high-quality broadcasting. The limited bandwidth available in the medium-wave band means that it would be impractical to increase the bandwidth of the signals there. Even if one accepted the poor interference performance, a channel spacing of 30 kHz or more would be required, giving around 30 channels in the medium-wave band, compared with the 114 available at 9 kHz spacing. This would be a diffi cult solution because medium-wave propagation characteristics mean that stations can cover very large geographical areas with relatively low transmitter powers, thus increasing the risk of co-channel and adjacent channel interference.