[TowerTalk] TH7-DX 15M problem

[john at kk9a.com]

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 at contesting.com>
Subject:	[TowerTalk] TH7-DX 15M problem
From:	"Radio K0HB" <kzerohb at 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