Friday, June 20, 2008

Street Car Interference

In America, electric-powered trolleys were debuted at a test service in Richmond, Virginia, in 1888. In 1910 the first regular trolley service began in Laurel Canyon a neighborhood in Hollywood California. Ten years later a similar service began on on Staten Island, New York. Philadelphia followed suit in 1923. (For the record I am defining trolley cars as any light rail car powered by an unshielded overhead wire)It was in this era, often even before consumers had radios, that the RF interference began. The problem begins in the basic design of the street car. The main chassis of the car relies on the rails for their ground connection. This is inconsistent and unreliable so at times it is in fact not grounded. This is not unlike a spark gap transmitter. The noise can be truly incredible. The overhead wires (catenary ) that provide power are also not perfect and at night one can see the arcs between them and the pantograph. these also produce very powerful RF.

The problem persists today despite the fact that "noiseless" electric street cars were in existence in the early 1930s. Noiseless street cars used SC-100 filters between the trolley and the feeder line. A second SC-2 filter was used at the electric motor. These cars were used in Hawaii and New Hampshire but for some reason they did not persist.