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Re: [TowerTalk] verticals above beams

Subject: Re: [TowerTalk] verticals above beams
From: jim Jarvis <>
Date: Fri, 23 Oct 2009 10:36:32 -0400
List-post: <">>
This discussion has drifted somewhat, from the original question,  
which was,
"how to I treat the radials?".    And the answer to that is,  you  
don't.   Can't do it
without tangling in the beam.    Can't effectively use the beam as  
radials, either.

THAT said,  I had a Cushcraft R7000 vertical about 5' above my LPDA  
on a 60'
tower, at our old place in VT.    The R7k is "ground independent", in  
that it uses
a choke system to decouple the feedline, and it feeds the vertical as  
if it were
electrically 3/8 wave long... something like a 200 ohm feed point.    
It has several
3' long whips, where you'd expect to see radials.   These are part of  
the decoupling

It worked just fine.   HOWEVER, it had a 3dB f/b ratio on any band  
covered by the LPDA!

What was happening was mutual coupling between the shields of the  
feedlines for each
antenna.   Some serious decoupling work was needed, to eliminate the  
common mode
currents from each feeder.  Once those chokes were in place, the  
"pattern" returned to normal.


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