"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