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[TowerTalk] grounding coax shields

Subject: [TowerTalk] grounding coax shields
From: Jim Jarvis <>
Date: Thu, 04 Jan 2007 12:40:16 -0500
List-post: <>
Actually, Jerry, the real reason for it is
to isolate the antennas from each other...more
than to protect the coax from lightning discharge.

In a direct strike, you can pretty much kiss anything
on the tower goodbye, anyway.

But feedlines run down 60' of tower, whether taped to
the sameleg, or opposing legs, will have some measure
of coupling.  You don't want that.

In VT, I had a beam, and a vertical 10' above it.
The feedlines came down the outsides of separate legs.
There were coil-chokes in both feedlines at the 

The vertical exhibited a 6dB f/b ratio, when I rotated 
the system. 

To eliminate it, I installed ferrite chokes topside, ran both
coaxes adjacent to each other, down the inside of one leg...
but tied shields to ground, top and bottom,  and then had
ferrite chokes again, coming off the tower.  The result was
good isolation, and no more f/b.  



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