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[TowerTalk] Tower resonant frequency

To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: [TowerTalk] Tower resonant frequency
From: Bill via TowerTalk <towertalk@contesting.com>
Reply-to: cqtestk4xs@aol.com
Date: Fri, 18 Sep 2020 00:27:06 +0000 (UTC)
List-post: <mailto:towertalk@contesting.com>
Plans are VERY slowly progressing for my new station in Belize.  Plans are for 
a 106 foot tower with lots of goodies on it.
Here's what is planned:106 ft of Rohn 55 guyed with Phillystran.  Three swing 
armed  Skyhawks at 32, 64 and 96.  Two A3WS WARCs at around 76 and 42 ft.  I 
plan on running four ropes to hold a wire 4 square surrounding the tower.  This 
is similar to what I had in KH6 and the 4 square worked well although the F/B 
was down to around 10-12 dB.  
My question is this:  I know the tower will have some effect on the 4 square 
surrounding it.  Obviously I don't want the tower to be anywhere near resonant 
on 80.  My guess is the top loading of the tower will lower the resonant 
frequency quite a bit, and the effective height will be around 145-150 ft, but 
I am not sure.  Obviously if it is in the range of around 130 it would be a big 
issue.
There is not enough room to put up a 4 square by itself so I'm stuck with this 
set up.  I do have some fiberglass poles that I could attach to the tower 
vertically to give it another 13 feet or so by running a wire up the pole and 
attaching it to the tower, but I really don't want to do that if I don't have 
to.
Thoughts on this?
73  Bill K4XS/KH7XS
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