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Re: [TowerTalk] TH7-DX 15M problem

To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] TH7-DX 15M problem
From: "Radio K0HB" <kzerohb@gmail.com>
Date: Wed, 26 Aug 2015 20:38:45 -0000
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Responding to Dave --- the amp works fine on a different antenna on 15M, and good as gold on all other bands on any antenna. Hard to suspect the amp.

Responding to Matt --- the SWR meter is external, downstream from the amp.

The balun is the 4K version, not the BN86 with the bad reputation. Hard to envision a balun weird on a single band.





-----Original Message----- From: David Robbins
Sent: Wednesday, August 26, 2015 7:43 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] TH7-DX 15M problem

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
--
"Just a boy and his radio"™
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