Measurements of Currents and Voltages down to a Wavelength of 20 Centimeters

The more common circuits in which diode voltmeters are used are discussed in Section I. The properties of these circuits are analyzed on the basis of the diode characteristics, with special reference to the input impedance. In Section II, two devices are described for current measurements, a hot-wire air-expansion device and thermocouples of special construction. Consideration of the requirements in the calibration of these devices in the short-wave range is followed by a layout which is described in detail, and with which calibrations down to a 20-centimeter wavelength could be carried out with an accuracy of within 1 per cent; one type of thermocouple proved exceptionally suitable for absolute current measurements. In Section III, it is shown how a diode voltmeter can be calibrated in the short-wave range with the calibrated current-measuring devices. Of the two arrangements described, one can be used down to approximately 3 meters and the other down to a wavelength of 75 centimeters. Diode voltmeters with diodes of special design exhibit at this wavelength a maximum deviation of 2 per cent from the calibrated values obtained with longer waves.