On Optimum Heterodyne Reception

Abstract

The use of the triode for anode rectification and cumulative grid rectification in heterodyne reception is investigated theoretically, and it is shown that:- (a) The amplitude of the combination tone produced in a radio receiver telephone reaches an optimum value for a certain value of the local oscillation amplitude. In anode rectification this phenomenon is due to the non-linear nature of the grid potential/anode current relation, while in grid condenser action the phenomenon may be due either to the non-uniform grid conductance or to the combined non-linearity of the relations between grid potential and grid and anode currents. (b) The optimum value of the local oscillation amplitude is independent of the received signal magnitude when the latter is small. (c) The magnitude of the combination tone is directly proportional to the strength of the signal oscillation when the local oscillation has been adjusted for optimum heterodyne. (d) The ratio of the optimum value of the combination tone to that produced with equal heterodyne is inversely proportional to the strength of the received signal. (e) The differential equation representative of grid condenser action is shown to be of a generalized Riccati type. dv/dt + f(v) = ϕ(t). Approximate solutions of this are obtained for practical cases. The optimum grid condenser value obtained theoretically in this way is in good agreement with the practical value.