The Theory of Heterodyne Receivers

The necessity of viewing the energy relations in the heterodyne receiver from the standpoint of average, not of instantaneous values, is pointed out; and the average energy present due to two currents of different frequencies is studied. A distinction is made between two general types of amplification; (1) by infusion of new energy into the received currents, and (2) by increase of efficiency of the receiving apparatus. Only the first may be regarded as true amplification. As examples typical of the second, the theory of the electro-magnetic and of the electrostatic telephone receivers is sketched. Finally, it is shown that the maximum true heterodyne amplification is four.