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[TowerTalk] 6m halo capacitor

To: Towertalk Reflector <towertalk@contesting.com>
Subject: [TowerTalk] 6m halo capacitor
From: Jim Hoge <knowkode@verizon.net>
Reply-to: Jim Hoge <knowkode@verizon.net>
Date: Fri, 4 Dec 2015 17:22:16 +0000 (UTC)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I have an old 6m halo of unknown manufacture. (Think Rohn 40 vintage.) It is 
about 37" in diameter and made from 3/4" aluminum tubing. The mounting bracket 
is cast aluminum in a tee shape. The gamma rod is fixed at 11". The capacitor, 
mounted on the halo and connecting to the gamma rod, is made like a small 
aluminum cup with what appears to have been a paper or cardboard like material 
as a dielectric between the cup and the inner, movable electrode (adjusted via 
a leadscrew.) With an MFJ-269 and leads less than 2", the cap reads 70pF at 
50.120mHz. 

Given the condition of the capacitor with the dielectric hanging out about half 
an inch, dried out, curling, and brittle, I am reluctant to use the antenna 
with any more than 10 watts at which it has not presented any problems. I would 
like to rebuild or replace the cap. If rebuilding the cap, what effect will a 
different dielectric material have on its value? I am guessing it would not be 
severe enough that the cap could not still be tuned back to a value of 70pF. 
Also, any ideas on the power handling capability of this unknown antenna?
Tnx es 73,Jim, W5QM

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