Re: Antennas guilty of RFI?

Dave Oldridge wrote:
"ZL2DG Dave" <zl2dg@xxxxxxxxxx> wrote in
news:fe68l2$jgf$1@xxxxxxxxxxxxxxx:

I believe antenna feedlines can be a source of rfi.The radiation from
an antenna should be much greater than any feeder radiation_why the
emphasis on feeder radiation? 73 de ZL2DG

Because feeders often pass near consumer electronics.

If the feeder has no antenna currents on it (like my feeder years ago when I had a vertical 250 feet out from the house), then the antenna, while radiating much more than the feedline is far enough away that the inverse square law protects the consumer electronics.

Of course this depends on antenna placement.

The improvement noted by increasing the distance between the radiating conductor and the consumer electronics (or power or other wiring they're connected to) can be much greater than an "inverse square law" would imply.

That's because a lot of the problems with interference occur in the near field of the radiating conductor. In the far field, the field strength is inversely proportional to the distance (the power density follows the "inverse square law"). But in some parts of the near field, the field strength varies as the inverse *cube* of the distance. So even a small increase in distance can often have quite a dramatic effect on interference level.

Roy Lewallen, W7EL
.

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