A Radio-Frequency Potentiometer

A potentiometer has been developed for the measurement of the amplitude and phase of voltages at frequencies up to at least 10⁶Cycles per sec. Two slide wires are used which carry currents whose phases are approximately in quadrature. A method of standardizing the instrument is described, that is, of determining the relative phase and ratio of amplitude of the currents carried by the two slide wires. Due principally to distributed inductance, the constants, especially the phase angles, of the best networks of resistances and capacities which may be built up are uncertain at 10⁶cycles. The method of standardizing is to measure a suitable network and then rotate the phases of the currents in the potentiometer, or in the network, by about 90 deg., leaving their ratio and relative phases constant. The voltages of the network are again measured and a simple calculation gives the constants of the potentiometer and of the network. The ratio of the currents in the two slide wires or dials may be determined to within one per cent, and their phases to 1/2 deg.