The traps would have been the first thing on my list also. Normally I would
not suspect the balun but you are running out of options. I am assuming
from your posts that you "upgraded" to the BN-4000 and I was curious what is
inside. I found this video which shows a non-terminated piece of coax
inside: https://www.youtube.com/watch?v=6txD51ysz24 . With all of the work
that you have done swapping the feedline and balun should be easy to try.
John KK9A
To: <towertalk@contesting.com>
Subject: [TowerTalk] TH7-DX 15M problem
From: "Radio K0HB" <kzerohb@gmail.com>
Date: Wed, 26 Aug 2015 19:21:49 -0000
I have an odd issue with a TH7-DXS.
A while back I started to see a higher-than normal SWR, just on 15M, and
just
when running some smoke.
While barefoot the problem never arises.
The problem never happens on 20M or 10M under any circumstances. I can put
a
brick on the key at full legal limit on those bands, and the SWR is 1:1
forever.
If I key down full power (actually any power over about 500W) the SWR will
be
fine for about 20-30 seconds, then will rise (not instantly, but "ramps" up)
to
about 2.5:1 across the 15M band. If I unkey, kill the amp, then key up
barefoot the SWR drops back to 1:1 and stays there forever.
It is as if something heats up under power, then changes value. BUT ONLY ON
15M.
I suspected one of the 15 traps, and hunted down a full new set for a very
nice
price.
This morning I replaced all of the 15M traps, and freshened up all the slip
joints in the antenna. It looks like new!
The problem persists.
Suggestions?
73, de Hans, K0HB
--
"Just a boy and his radio"T
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