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Re: [TowerTalk] TH7-DX 15M problem

To: towertalk@contesting.com
Subject: Re: [TowerTalk] TH7-DX 15M problem
From: David Robbins <k1ttt@verizon.net>
Reply-to: k1ttt@arrl.net
Date: Wed, 26 Aug 2015 14:43:33 -0500 (CDT)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
a problem with the amp?


Aug 26, 2015 03:28:05 PM, kzerohb@gmail.com wrote:

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
--
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