AM radio reception

With regard to your comments about AM radio reception in Carsguide on July 19 I would like to offer the following comments as a retired electrical and communications engineer. You correctly pointed out that AM is not getting much air-play these days due to FM, CDs and iPODs. Notwithstanding that, while modern cars have a very high standard of interference suppression much of the interference experienced by Mark Fenton results from "tracking" on high voltage power line insulators. Dirt and dust accumulates on the pole-mounted insulators and in Victoria the main high voltage is 22,000 volts. With even slight conditions of moisture or rain, this causes the formation of small arcing currents across the insulators, often referred to as "tracking". In itself this is not too serious and is normally not visible at least in daylight, but this "tracking/arcing" causes electrical noise that affects AM radios. In fact, AM technology has been used to detect "leaky" insulators. In past times, insulator washing was well practiced, but with the advent of our privatised electrical distribution systems, reduced washing programs are aimed to save maintenance costs. Since there are no real standards to determine what are or are not reasonable levels of AM interference car drivers are expected to tolerate, the reduced washing programs are pushing the boundaries. I live in Geelong and there are "horror" points with my Ford Territory TS, but in other areas of Geelong, AM reception from Melbourne is just fine. Trust this helps.