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

Roy Lewallen · July 28th 07, 12:21 AM posted to rec.radio.amateur.antenna

wrote:
I am curious as to whether RF exposure concerns are greater for a
small transmitting loop [like the MFJ tuned loop] compared to a dipole
radiating the same power. It would seem that close to the loop, the
RF power density may be greater [than it would be at the same distance
from the dipole apex] since the radiating volume is smaller. Can I
just assume that the power is evenly distributed on the surface of a
sphere having a radius equal to my distance from the loop antenna,
calculate the power density on the sphere surface, and use that number
for evaluation - or are there some near-field considerations not
captured using this approach?

Thanks,

-JJ

The method you describe is valid only in the far field. There are higher
order terms to the field strength (field relative to distance) in the
near field, and they're strongly a function of the distance and the
antenna geometry. Using the method you propose can produce very
erroneous results close to the antenna.

Roy Lewallen, W7EL