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Re: [TenTec] Omni VII: Need Help with a Strange Problem

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Omni VII: Need Help with a Strange Problem
From: Stuart Rohre <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 14 Dec 2010 16:25:40 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
While I have not had the problem you have on an Omni VII, I have had it 
with another Ten Tec rig.  Only it was not the fault of the rig.  It was 
a bad coax jumper cable to an antenna switch.  The shield was making a 
bad connection, and was affected by movement or thermal warm up.

Other causes could be a loose ground lug, loose connector internal to 
the rig, or anything inside that is acting as a RF ground, but is loose 
and affected by rig operating temperature cycles.  I don't think it is a 
"component nearing a failure".  It is something that is thermally 
affected, and those are usually loose connections of some type. It could 
even be a solder joint that was missed, or did not wet completely and 
provide a low impedance ground.  Check in the circuits of the ATU, after 
trying new or known good coax jumpers.  Do you have a grounding lead 
connected to the back of the radio, and is it tight, at both ends?  The 
only components in the ATU are fixed inductors and capacitors, switches 
or relays, things that don't typically gradually fail.  (With the 
exception of relays that in some types acquire permanent magnetism after 
many, many uses.)  Look for things that could move with thermal cycling, 
loose connections, and then look a the solder joints.  A strong light 
and a magnifier can help with those.

Let us know, what you find.  I don't expect a reset to help, so would 
leave that to last after all other options.  As simple a cause as a PL 
259 not completly tight can cause such an RF connection problem as to 
cause feedback.

-Stuart Rohre

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