Induced insulator voltage in transmitter antenna guy cables

A method is examined for the analytical determination, with very good accuracy, of the RF voltage that will be developed across insulators in antenna guy cables. The Numerical Electromagnetics Code was used to develop the predictions, which were then compared with measurements conducted on a model antenna. Calculated and measured values of the mutual impedance (the ratio of induced voltage to antenna feedpoint current) were obtained for a scaled configuration containing a vertical radiator and one top-loading guy cable. Eighteen test conditions were examined, with nine insulator location patterns (i.e., one to five insulators) and two insulator capacitances. For those test conditions chosen to represent realistic antennas, the mean and maximum differences between calculated and measured mutual impedance values are 0.12 and 9.93 percent, respectively. The small difference indicates that the method is well suited both to engineering design considerations and to the investigation of the adequacy of insulator withstand voltages at existing transmitter sites.