A New Method for the Calibration of Ammeters at Radio Frequencies

This paper describes the construction and operation of a thermionic vacuum tube which is designed for the measurement of radio-frequency currents. The input circuit consists of a filament whose cross section is small enough that the "skin effect" is negligible at thefrequencies used. The filament is heated first by currents of known magnitude (at a low frequency) and again by radio-frequency currents to be measured. Electrons emitted by the heated filament are drawn to an anode sealed into the tube and a comparison of the resulting space currents indicates, if the necessary precautions are taken, the amount of current in the input circuit.