A Method of Measuring the Amplification of a Radio-frequency Amplifier

Abstract

The audio-frequency oscillations were generated by means of a tuning fork, which was maintained in vibration by a triode valve. The alternating-current voltage from the plate circuit of this valve was applied through a transformer to the plate circuit of a feeble radio-frequency oscillator. The radio-frequency oscillations were in this way separated into alternate semi-period trains of waves. The input energy to amplifier was controlled by a sliding coil inductance. The radiating coil of this was loosely coupled through an auxiliary coil with the oscillating coil of the radio-frequency generator and the receiving coil was connected to the tuned receiving circuit of the amplifier The receiving coil of this inductance was adjusted so that the intensity of the rectified oscillations, as received through the amplifier by the telephone, was the same as that of a standard source of sound of the fork frequency. The latter standard was furnished by applying a small alternating-current voltage from the fork alternator circuit to the receiving telephone. The voltage amplification under these conditions is the ratio of the mutual inductances of the sliding coils (1) without the amplifier and (2) with the amplifier. A method of calibrating the mutual inductance and also methods of eliminating strong radiation are detailed in the Paper.