Direct conversion s.s.b. receivers: a comparison of possible circuit configurations for speech communication

Direct conversion single sideband receivers are of interest because they are less subject to spurious responses than the conventional superheterodyne, do not entail the use of high-gain narrowband amplifiers with high centre frequency, and lend themselves better to integration in monolithic form. Two approaches to the design of receivers of this kind have been described: (1) the phasing technique, in which the local oscillator is tuned to the nominal signal carrier frequency and the unwanted sideband response eliminated by phase cancellation; (2) Weaver´s `third method¿, in which two oscillators are used, the first tuned to the centre of the incoming s.s.b. spectrum, and the second to the centre of the reconstituted a.f. spectrum. The characteristics of the two types of receiver are compared, and the superiority of the relatively neglected Weaver approach, particularly in a new a.c. coupled variant, is demonstrated, so far as the reception of speech modulated signals is concerned.