[TowerTalk] Antenna problem?

[Peter Chadwick]

>Plug it into the FT-990 and the swr on the rig was 3:1. Antenna tuner was 
off. Add different lengths of RG-8, the swr varied from 2.5:1 to 5:1.  It 
doesn't seem to be wx related. < 

I'd suspect common mode currents on the coax outer. Some ferrite rings or clip on sleeves, plus a couple on the mains lead would be the first place I'd try. Plus, have you got a good RF ground on the radio? Or still got a good RF ground on the radio? I ask that because I had a ground on my antenna tuner consisting of 6 inch wide aluminium flashing running back to the tower. Checked the continuity last weekend - it was 80 ohms. The aluminium had corroded through just below the sod.

73

Peter G3RZP




========================================
Message Received: Oct 06 2005, 04:46 PM
From: K7LXC at aol.com
To: towertalk at contesting.com
Cc: W7FPChuck at aol.com
Subject: [TowerTalk] Antenna problem?

Howdy, TowerTalkians --

I've got an antenna problem and I'm stumped. An M2 15M monobander 
developed some high swr - 3:1 or more where it used to be 1.1:1.

I took a crane and man-basket up to the feedpoint and measured the swr 
with my MFJ at the balun; it was 1.2:1. I next measured at the jumper to the 
tower - same thing. Then I measured the end of the feedline in the shack - same 
thing. As far as I was concerned, the antenna system was fine.

Plug it into the FT-990 and the swr on the rig was 3:1. Antenna tuner was 
off. Add different lengths of RG-8, the swr varied from 2.5:1 to 5:1. It 
doesn't seem to be wx related. 

Like I said, I'm stumped. Any help out there? Solutions appreciated!

Cheers,
Steve K7LXC
TOWER TECH 
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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