A Method for Accurately Measuring the Vertical Electric Field Strength of a Propagating VLF Wave

Ideally, the vertical electric field strength of a propagating VLF wave can be measured by observing the terminal voltage of a short dipole antenna placed in the field; but, in applying this principle a number of practical difficulties are encountered. Methods of overcoming these difficulties have been studied using a working-model field-strength meter of convenient dimensions. Such a device can be calibrated with reference to standards of voltage and length and, hence, offers a fundamental advantage over the use of vertical antennas and ground screens. It also provides an alternative to the common practice of estimating the electric field by measuring the associated magnetic field and applying a conversion factor. Evidence is presented to indicate that this latter method may sometimes be subject to experimental or interpretational difficulties. Error analysis shows the present working model is capable of measuring VLF field strengths to an accuracy of about 5 per cent.