The Amplification Obtainable by the Heterodyne Method of Reception

The author contrasts the Cohen theory that heterodyne amplification can be increased indefinitely by increasing the local current (using an ideal detector of unlimited current-carrying capacity) with the Liebowitz theory that the maximum "true heterodyne amplification" is four. It is then shown by several different methods of considering detector and heterodyne action as compared with chopper detection of received energy, that if the detector gives an audibility current proportional to the received current, the maximum amplification of audio power is 2.43, and does not increase indefinitely with the local current. With detectors giving an audibility current proportional to the square of the received current (e.g., ordinary contact detectors thru a considerable range), the amplification may greatly exceed four, and its excess over four cannot be accounted for on the basis of "increased detector efficiency," since a steady polarizing current will not produce the same increase.