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Author Topic: Suddenly SWR  (Read 1277 times)
AA1ZH
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Posts: 8




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« on: September 13, 2005, 12:00:40 PM »


I have an Icom 706IIG that I'm running mobile, with a High Sierra Sidekick.  Suddenly, my SWR is high (off the chart), on all HF bands.

What I don't understand is that if it were a grounding issue, why was it tuning before?  I've taken a close look at connections and cables, but nothing's jumping out at me.

If anyone has some specific suggestions on what to check, or what it could be, I'd appreciate it.

FWIW, I noticed there's similar (but not identical) issues posted here:

http://www.eham.net/forums/MobileHam/7327

Thanks.
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K0BG
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« Reply #1 on: September 13, 2005, 06:46:27 PM »

First, everyone seems to jump to the conclusion that problems like this are grounding issues. They're typically not. If you are sure that the coax feed is not the problem, then most likely, it is the finger stock or a poor connection at or near the top of the coil.

Unfortunately, all screwdriver type antennas (except the HiQ) change length as you adjust the frequency. The sleeve over the moving parts may indeed be well sealed, but sooner or later, dirt and grime take their toll. Further, because of their innate construction, they flex a lot particularly when set on the lower frequencies. This also adds to the finger stock woes.

The best way to run down the problem is to use an antenna analyzer. Connect it at the base of the antenna, not at the radio end of the coax. The coax should be checked by itself.

Alan, KØBG
www.k0bg.com
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N3ZKP
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Posts: 2008




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« Reply #2 on: September 14, 2005, 11:56:50 AM »

Alan,

FYI ...

The Hi Sierra antennas do not use finger stock for the very reason you mention. Jim Heath uses a torrus(sp?) shaped spring that fits in a grove in the outer cover of the coil.

I do agress this is one place I would look, however.

If the SWR is equally bad everywhere, I'm betting on a feedline problem, especially where it connected to the antenna mount itself. If not properly sealed, water WILL get in and cauee problems.

I have my connection double-wrapped with Scotch 33 and then covered with Plasti-Dip.

Lon
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WB2WIK
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« Reply #3 on: September 14, 2005, 04:25:52 PM »

"Suddenly SWR" might make a good name for a new TV sitcom.

I did some work on the "Suddenly Susan" set when the Brooke Shields sitcom was active.  Your title here reminded me of that.

"Suddenly SWR stars a mobile ham radio operator who finds his antenna out of whack.  He goes nuts, asking all his friends, and even strangers, to see if they can help.  In the process he dismantles his entire vehicle down to the rocker arms, and then can't get it back together again!  You'll scream in delight watching this fabulous new show, coming to CBS on October 6th."

Just a thought.

WB2WIK/6
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K0BG
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« Reply #4 on: September 14, 2005, 06:58:52 PM »

Brian, you'll have to excuse Steve. He's one of those guys who stays up at night. I know this as I hear him occasionally when I first get out of bed of a morning and turn the radio on. Just don't get him started on roving.

Alan, KØBG
www.k0bg.com
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KE4SKY
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« Reply #5 on: September 19, 2005, 05:54:05 AM »

Disassemble all connections in the antenna mount, and clean parts thoroughly to remove any and all corrosion.  Coat all connecting parts and assemblies with Penetrox or similar anti-sieze/anti-oxidizing compound and reassemble to factory specs.  Road salt, moisture, dirt, etc. all get in there and cause problems.  This should be a part of your annual spring maintenance after the winter season on all of your mobile antenna mounts.  
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KL7IPV
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Posts: 984




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« Reply #6 on: September 19, 2005, 07:34:38 PM »

Check the coax where it rounds any corners. Maybe the insulation has crushed around the center conductor and is shorted or a very low resistance to the RF when you fire it up. Try using a different piece of coax from the radio to the antenna and see if that corrects the trouble. If so, the coax is the problem. Good luck.
73,
Frank
KL7IPV
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