Paul Schlyter wrote:
In article <PMKdnT8QOMBqfj7fRVn-qw@comcast.com>, mjmahon@aol.com says...Anyone who lives within a couple of blocks of a radio station transmitter will appreciate some shielding on their video cables.Well, that depends on how the radio station is built.... Do you have your radio stations on the rooftops in your city? Here i Stockholm, our major radio station resides in a mast some 1000+ feet high, a bit outcide the city. The mast itself was built in an unpopulated field -- nobody lives "a couple of blocks" from it. A number of people do live within a mile from it though, and since the mast is so high, the signal there is so weak that a low-power local transmitter was built for that area of the city.
In the U.S., large cities often cluster antennas on tall buildings or large masts--but not all. And in many cities, AM and FM transmitters are scattered in the city and the suburbs, so many people are relatively near a transmitter. In addition, most cities have numbers of radio amateurs with up to 1KW transmitters, perhaps next door. The case you cite (a mast with a weak signal at its base) is typical of VHF antennas with nulls above and below the antenna. Most of the transmitted power is directed into a thin disk-shaped lobe for a gain of several dB over a simple dipole. In the suburb I grew up in, there was an AM radio station about a mile away, and its signal would induce 50-100mv in a wire a few feet long. Needless to say, all signal cables required shielding. ;-) It was powerful enough that an unamplified crystal set receiver could drive a speaker and be heard throughout a quiet room! -michael 8-voice music synthesizer using NadaNet networking! Home page: http://members.aol.com/MJMahon/