I had a huge coax choke at the feedpoint of my 160 m. inverted L (see
http://www.qrz.com/K5UJ for a photo). It was made with 100 feet of 213
wound on a 20 gal. garbage can, which had around a 16 or 18 inch diameter.
The choke gave a lot of inductive reactance (if my calculation was correct)
for common mode rf on 160. The downside was that it also lengthened the
feedline by 100 feet and that together with the feed out from the shack,
added up to a surprising amount of loss, even on 160--probably not enough to
be noticed but more than I expected. I view antennas, feeds, transmatches
etc. as a system. A little loss here; a little loss there, and pretty soon
you're into some big losses, hi hi (to corrupt what some congressman once
said about money). Anyway, with 101 radials on the ground, I eventually
found that the amount of return rf current on the outside of the coax was
insignificant, removed the choke and never noticed a problem with it gone.
so what's the point--the point is that if you have enough radials, the
distribution of return rf is so extensive, there isn't going to be much on
the coax shield and you can probably do without the choke. How many radials
I don't know. probably more than 20 but less than 100.
Rob / K5UJ
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