Coherent and non-coherent demodulation of envelope-modulated radio signals. With particular reference to the enhanced-carrier system

The ordinary ¿linear detector¿ and the coherent demodulator are briefly discussed as the two extreme cases of demodulators for envelopemodulated signals, since in the former the rectifier (or modulator) is switched by the complete input signal, while in the latter a pure local reference tone is used. The synchrodyne and enhanced-carrier systems are regarded as intermediate cases in which the switching is effected by an impure carrier derived from the incoming signal. The enhanced-carrier system, using filters to extract the carrier from the incoming signal, appears to have received little attention in the literature; and the distortion caused by tuning errors in the enhanced-carrier path and the interference due to unwanted input signas are here particularly considered.