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
--
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