RadioBanter - View Single Post - RF Exposure from Small Transmitting Loops

Roy Lewallen · July 28th 07, 08:10 PM posted to rec.radio.amateur.antenna

wrote:
Thanks all.

Roy, I was not implying that I believe one can assume that the power
is from a point source and one can consider the power density passing
through a sphere to determine RF safety. I was looking for some
guidance as to how to determine a "safe" distance from a small tuned
loop assuming a particular frequency and power.

It appears that the simple sphere approach works reasonably well
beyond a wavelength or so, and may be an acceptable first-order
approximation at 1/2 wavelength [from a small loop].

There's no distinct boundary between the near and far field, but at a
wavelength, or even a half wavelength, you're pretty much in the far
field of a small antenna. So far field approximations such as the one
involving power density on the surface of a sphere are quite reasonable
at those distances.

Roy Lewallen, W7EL