Electrical Measurements at Wave Lengths Less than Two Meters

In this paper the measurement of power and voltage at ultra-short waves is considered. A signal generator delivering adequate power output with satisfactory stability over the wave-length range from twenty to 200 centimeters is described. The requirements of thermocouples satisfactory for the measurement of power are considered and a set of thermocouples covering the power range from 0.1 milliwatt to fifty watts is described. A study of vacuum tube voltmeters has shown that diode voltmeters have very small loading (of the order of 10
⁵
ohms) on the circuits to which they are connected, whereas conventional triode voltmeters using RCA-955's have an input impedance of about 10
⁴
ohms at a wave length of one meter. The errors of diode voltmeters at ultra-short wave lengths have been studied and found to be of two kinds: 1. An error due to partial series resonance between the lead inductances and the interelectrode capacity. 2. An error due to a transit time effect. This has been called "premature cutoff." These errors have been studied experimentally and theoretically, the results being in qualitative agreement. In the course of the experimental work very small diodes have been built, the smallest diode having an anode diameter of only 0.0065 inch. Calibrations for these diode voltmeters have been obtained.