On 5/3/2014 6:49 AM, Jim Lux wrote:
With coax, if you find that the shield is picking up RF current and
re-radiating, you can throw a choke on it to stop that.
But ONLY if the SWR at the feedpoint is in the reasonable range (5:1 or
better), and only if it is a serious choke (high choking Z). N6BV has
shown (and I have verified his work) that in extreme cases -- for
example, an 80M dipole loaded on 40M -- high power will very quickly fry
a choke at the feedpoint.
Bottom line -- all band dipoles and OCF antennas are a very bad idea in
today's world where RF trash is everywhere. I view them as an unnatural
act. Yes, you can load a random dipole fed with high Z line and get it
to accept power, but the pattern will vary widely with frequency (lots
of nulls), and because you can't choke the feedline, it will pick up
lots of noise.
There ain't no free lunch. Resonant antennas fed with coax rock. The
others "roll."
73, Jim K9YC
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