Corrective Measures for Minimizing the Interaction of Power Lines with MF Broadcast Antennas

New high-voltage power lines are often built in close proximity to MF/AM broadcast antennas. The "skywire" which joins the tops of the power-line towers creates closed loops for RF current on the power line and its image in ground, and these loops can be resonant in the MF band. If the broadcast antenna operates on such a resonant frequency, it induces large currents on the skywires and power-line towers, and "reradiation" from these induced currents can considerably alter the broadcast antenna's radiation patterns. This paper uses computer modeling to systematically examine several techniques for "detuning" the power line, namely: isolating towers from the skywire, series insulators in the skywires, stub detuners on the skywires, and short capacitively terminated stub detuners on the towers. The mechanism which makes each detuner effective is seen from the RF current distribution computed for the power line and detuner. The bandwidth of each detuner is assessed. Consideration is given to the difficulties that can arise in the implementation of each detuner design on a real power line. All of these detuner designs have been tested by scale-model or full-scale measurements. Only when detuning has been made a systematic economical procedure can this special EMC problem be regarded as solved.