SCATTERING FROM POWER-LINES WITH THE SKYWIRE INSULATED FROM THE TOWERS

This paper studies the distortion of a commercial AM radio station's r adiation pattern due to scattering from a power line with steel lattic e towers which carry a skywire that is insulated from all the towers. Despite the insulated skywire, the towers couple strongly to the skywi re. The resonant behavior of the power line spans is similar to that d escribed in previous papers with the skywire connected to all the towe rs. However, die resonant frequencies are much higher when the skywire is insulated and the strongest resonance falls above 1000 kHz for typ ical power line dimensions. This paper models a real site consisting o f a directional broadcast array at 1380 kHz and a power line with 29 t owers. Although the resonances of the power line fall at much lower fr equencies than 1380 kHz, the antenna induces substantial RF current fl ow on the towers and skywires of the power line. The power line scatte rs strongly into the minimum in the station's radiation pattern and th e station's protection requirements are seriously violated. Thus, the towers of the power line will need to be treated with detuning stubs t o restore the pattern to its intended values.