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[TowerTalk] SWR shifts with power

Subject: [TowerTalk] SWR shifts with power
From: "Howard Klein" <>
Date: Tue, 24 Jan 2006 21:05:05 +0000
List-post: <>
I had a similar problem with the same symptoms. In my case it seems my shunt 
wire, actually 3/8" cu tubing, got blown close enough to the tower for it to 
arc with high power. Hope your solution is that simple.

I'm having trouble with my shunt-fed 15m tower. I have an L matching
network that is switched between 80 and 160m. A relay selects
different taps on the inductor, and also adds capacitance for 160m.

If I use an MFJ 259 antenna analyzer, I can get a nice match on
either band. And if I transmit with a few watts, I have no problem.
Even the 20 watts that the KAT100 uses isn't a problem.

However, if I transmit about 70 watts or more, the SWR suddenly
shifts to 3:1 or worse. It changes with each transmission.

I thought the caps might be arcing, so I replaced one of them with a
wide-spaced variable, same problem.

Any suggestions?

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