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Re: [TowerTalk] Horizontal tower movement at the top

To: "Gerald Boutin" <>,<>
Subject: Re: [TowerTalk] Horizontal tower movement at the top
From: "Roger (K8RI)" <>
Date: Tue, 8 May 2007 11:28:53 -0400
List-post: <>

> Clay,
> If you stick a 25G on a pier pin, you can pretty much ignore what typical
> tower movement might be. The tree is going to be holding up the tower.
> I sort of liked the suggestion to put up a ladder instead. So, what would 
> be
> a good ladder? How about 100 feet of 25G?
> If you still want an answer to your initial question, it is relatively 
> easy
> to approximate when you know how much guy wire stretches and use the data
> from the Rohn catalog and the law of cosines equation.
> Law of Cosines Equation
> (
> Guy Wire Stretch
> 6.77 inches of stretch per 100 feet of 3/16" EHS when under a 3000 pound
> load

That only tells the stretch to get to that tension. The figures you need to 
work with are the wind load in pounds at  each attach point added to the 
cable tension vector.

Roger (K8RI)

> --
> Gerald Boutin, VE1DT
> From: "W7CE" <>
> Subject: [TowerTalk] Horizontal tower movement at the top
> To: <>
> Message-ID: <270a01c79024$6357f680$3500000a@claylaptop>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
> Does anyone know how much horizontal movement is considered acceptable at
> the top of 100' tall Rohn 25G, 45G and 65G towers?  I don't see any 
> mention
> of it in the Rohn catalog.  I know that the tops move, I just don't know 
> how
> much is considered normal.
> I'm considering a rather unusual tower installation at my QTH.  Because of
> large trees that occasionally lose branches during wind storms and 
> property
> line constraints, a guyed tower isn't practical.  For years I've had my 3
> element yagi on top of a 95' Doug Fir tree and it has worked well there. 
> I
> watched it during our record setting wind storms last winter and the top 
> of
> the tree was only moving about 6-7" (less than the diameter of my Ham IV
> rotator).  This is a big tree with a 42" diameter base and an 8" diameter
> stump at the 95' level where the antenna is mounted.  The problem with 
> this
> installation is getting up to the antenna to do maintenance, plus I'm
> planning on replacing it with a new SteppIR as soon as I figure out how 
> I'm
> going to mount it.  What I'm thinking about doing is installing 100' of
> tower as close to the tree as practical (less than 3') and attaching it to
> the sides of the tree with angle iron at 20' intervals.  With this 
> approach,
> I don't think the tower could ever come down unless the tree itself did
> also, which is unlikely based on our soil type and the excellent health of
> the tree.  I would then mount the antenna on the top of the tower.  This
> would give me a much easier way to climb up to the top.  I can use 25G, 
> 45G
> or 65G for the installation, whichever would be best.  25G would be the
> easiest to install because of it's weight and I suspect that it is the 
> best
> choice.
> I'm looking for opinions on the viability of this solution.  Will the
> movement of the tree in the wind stress the tower too much or will it 
> about
> the same amount of movement that a guyed tower would normally experience 
> in
> a big wind?  Opinions?  Suggestions?  Am I thinking a little too far 
> outside
> the box?
> 73,
> Clay  W7CE
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