Antenna-Measuring Equipment

A self-contained equipment (with exception of batteries), of portable design, for measurement of apparent capacity, apparent resistance and natural frequency of antenna-ground systems, within specified limits, is described. A substitution method is employed, adjustment of the calibrated phantom antenna being made to maintain constant frequency and constant amplitude of oscillation in the driving oscillator circuit, as the oscillator is switched from the physical to the phantom antenna. In measurement of the natural frequency of the antenna, the antenna frequencies corresponding to various amounts of loading inductance are determined. A curve is then plotted and extrapolated to the zero loading ordinate. A very close approximation is obtained if the inductance of the small coupling coil is neglected, the antenna frequency with the coil in circuit being taken as the natural frequency. The sensitivity and accuracy of the apparatus is discussed with attention to the imperfections of the phantom condenser and resistance. The results of measurements on a calibrated dummy antenna, as well as on a ship's antenna, are given in graphic form. The effect of interfering signal voltages picked up by the antenna from nearby transmitters is considered.