High-Frequency Measurement of Electric Fields Using a Telemetering Probe

When image plane construction is impossible, accuracy of field strength measurements is greatly reduced by the presence of connecting cables and apparatus. This problem may be circumvented by telemetering the field information to a distant control station. This paper describes a system designed to measure relative electric field strengths at 26 MHz. The sensing probe employs a voltage comparison technique, and a telemeter whose output drops to a sharp null when a specific electric field is present at the probe. If calibration is desired, the specific field may be measured, or deduced through probe circuit analysis. The system gives better than 0.1 dB accuracy if care is taken in positioning the probe. If a large scattering field obstacle is at least 10 meters from the probe, errors in relative field measurements will be less than 1 percent due to the presence of the probe. Various suggestions are given to decrease the effects of some sources of inaccuracy. The probe system may be applied in almost any medium, providing that temperature excursions are not too drastic.