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Re: [TowerTalk] Antenna problem?

To: <g3rzp@g3rzp.wanadoo.co.uk>
Subject: Re: [TowerTalk] Antenna problem?
From: "John Wagner" <jwagner@dxengineering.com>
Reply-to: jwagner@dxengineering.com
Date: Fri, 7 Oct 2005 08:37:00 -0400
List-post: <mailto:towertalk@contesting.com>
If the SWR or the resonance of the antenna changes with feedline changes,
you have common-mode current on the feedline. Ground are important as well.

73 John
> 
> >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@aol.com
> To: towertalk@contesting.com
> Cc: W7FPChuck@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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