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![]() "Bob Miller" wrote in message ... On Sat, 28 Jan 2006 07:25:58 -0500, "Lenny" wrote: Great pix, thanks Weatherall. Does the Ferrite Rod only aid in AM broadcast reception, or does it also aid SW reception? Lenny In most AM/FM radios, the ferrite bar antenna is for AM reception only. A separate whip antenna for FM is reasonably close to a quarter wavelength on the FM frequencies; a 1/4 wave whip antenna on the AM band, 530 to 1700 Khz, would be hundreds of feet long, hence the shortened AM antenna using the ferrite rod. But a SW whip antenna is usually much less than 1/4 wave, as well. The whips can be resonated with additional components, but they usually aren't. It isn't necessary. On little radios, the rod is a couple of inches long, on others such as the C.Crane CCRadio or the GE SuperRadio the rod is bigger, about 8 inches long, hence their supposed "DXing" capabilities for AM. On shortwave radios, I'm not sure which frequencies the ferrite bar would be used for, certainly the American AM broadcast band, not sure about others. Radios with a longwave band would also use the ferrite rod antenna for that band. I've seen radios, such as the Realistic DX-100 which use a ferrite antenna for each of the SW bands. In the case of the DX-100, the antenna is used mostly as the inductance of the input tuned circuit. Nearly all the signal power on SW comes in through a whip or external antenna. Moving the radio has practically no effect on the signal or interference. One disadvantage to the whip antenna, it is vertical, and vertical polarization picks up more manmade interference. Horizontal antennas such as the ferrite bar are a little more immune. Bob k5qwg On most radios, the whip doesn't have to be vertical. Sometimes interference can be minimized by moving the whip, although it often doesn't make much difference. The horizontal ferrite bar radio antenna is magnetically horizontal, but electrically vertical, just like the whip antenna. However, the ferrite antenna is much less prone to capacitive noise pickup from whatever electronic stuff is running. Frank Dresser |
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