Effects of Power Line Re-Radiation on the Patterns of a Dual-Frequency MF Antennae

A detailed computer simulation of AM broadcast reradiation from a power line is described and the computations compared with measurements. The power line is in the vicinity of the London, England two-frequency directional antenna array of the U.K. Independent Broadcasting Authority. A simplified equivalent computational model is derived for the individual power line towers, and the ground effect due to the tower footings is estimated. The computational model includes the overhead ground wire (skywire) but excludes the power carrying wires. Computations are described for the power line induced currents and for the antenna radiation patterns as modified by the power line currents. The comparison of the computed results with full-scale radiation pattern measurements shows sufficient quantitative agreement to support the utility of computational predictions for power-line re-radiation. The frequency sensitivity of the re-radiation is studied theoretically and found to have a noticeable effect for deviations of ±10 kHz.