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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