Scattering from power lines with the skywire insulated from the towers

This paper studies the distortion of a commercial AM radio station´s radiation pattern due to scattering from a power line with steel lattice towers which carry a skywire that is insulated from all the towers. Despite the insulated skywire, the towers couple strongly to the skywire. The resonant behavior of the power line spans is similar to that described in previous papers with the skywire connected to all the towers. However, the resonant frequencies are much higher when the skywire is insulated and the strongest resonance falls above 1000 kHz for typical power line dimensions. This paper models a real site consisting of a directional broadcast array at 1380 kHz and a power line with 29 towers. Although the resonances of the power line fall at much lower frequencies than 1380 kHz, the antenna induces substantial RF current flow on the towers and skywires of the power line. The power line scatters strongly into the minimum in the station´s radiation pattern and the station´s protection requirements are seriously violated. Thus, the towers of the power line will need to be treated with detuning stubs to restore the pattern to its intended values