Calibrating Ammeters above 100 MC

A survey is made of the progress to date in measuring current above 100 mc. The types of vacuum thermocouples available for ultra-high frequency current measurement are discussed and the several methods of calibration are reviewed. A calorimeter method and a thermistor bridge method are presented. The advantages and limitations of the calibrating methods are brought out. The electrodynamic method is particularly suited to large currents, the calorimeter method to medium currents, and the thermistor bridge method to small currents. The importance of obtaining agreement between methods that do not depend on the same principles is emphasized.