On Thu,9/3/2015 12:33 PM, David Cole wrote:
My only conclusion now is that the two loops are coupled by the 26 foot
aluminum boom.
Hi David,
I've been studying this antenna too, and have built an NEC model. After
reading your email, I added a grounded tower and boom arm to the model,
and it did NOT degrade performance. I've not built one of these
antennas, and am quite interesting in hearing from those who have.
What chokes are you using (complete details -- what core, how many
turns), and exactly where are they located? Are you mounting the coax
close to the boom?
If I were doing it, I would use 16 turns of a transmission line formed
by a pair of #14 THHN around a #31 core. That is, measure out two 5 ft
lengths of 314 THHN, tape them together, and wind 16 turns of that pair
around the core. The Zo of that choke is on the order of 90 ohms.
What matters is to decouple the feedpoint from both the coax and a
conductive boom, so I would locate the chokes at the feedpoint of both
loops, between the feedpoint and the boom.
73, Jim K9YC
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