Characteristics of demodulated narrowband SSB-FM signals

Bandlimited SSB-FM is analysed in terms of its complex zeros, leading to expressions for the spectral components of both modulated and demodulated signals as a function of the zeros. These confirm that direct distortionless reception is feasible if the modulating signal is sufficiently small. The characteristics of the bandlimited SSB-FM signal and the demodulated signal are analysed, and it is shown that demodu lation distortion caused by overmodulation consists mainly of positive `clicks¿¿. These occur simultaneously with envelope dips, and their frequency may be taken as a measure of distortion noise. Computer simulation provides illustrative examples concerning the use of SSB-FM for speech transmission through a conventional SSB channel, and bounds on the frequency deviation are obtained for this example. The effects of both realistic IF filters and mis-tuning at the receiver are also investigated. The results suggest the potential of narrowband SSB-FM for applications such as mobile radio.