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[TowerTalk] Glen Martin + Cushcraft A3S

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Subject: [TowerTalk] Glen Martin + Cushcraft A3S
From: (
Date: Mon, 21 Jun 1999 11:21:34 EDT
In a message dated 99-06-20 22:18:01 EDT, writes:

> Finances aside when building a tower, I am planning on putting up a 
>  GM Enginnering RT-424 (the 4.5' model -- hope the model # is right)
>  with a Cushcraft A3S on top of it.
>  Both Cushcraft and GM say that this is an acceptable combination 
>  the mechanical specs of the A3S and what the tower is rated for, my 
>  windzone of 70MPH.  The caveat of course is I must meet or exceed their
>  installation reccomendations (which I of course intend to do...)
>  Does anyone feel I'm in left field here....?  I know that one of the big
>  rules is following the manufacturer's specs and they're in agreement with
>  what I'm doing but I'd like some opinions on this....comments?

     Sounds okay to me. I've installed over a half dozen GME roof towers and 
they can be sturdy antenna supports if installed properly. The roof-top tower 
is rated at 6 sq.ft. @ 87 MPH so you're not violating anything I can see. 

      The crux of course is anchoring the tower to the roof. I don't use the 
lag screw method that the GME tower feet are drilled for. Rather I use one 
piece of all thread that goes through the foot and roof and then through a 
backing plate inside the attic. This gives you a roof truss sandwich with big 
washers and nuts on both ends. If you're not sure that the roof structure is 
strong enough, add some more braces and reinforcing. The forces and bending 
moment of your proposed installation is reasonably small so adequate 
engineering should be easy.

      The majority of roof mounted systems I've installed have been the 
9-foot tower and a Force 12 C-3, C-4, C-3SS, etc. This system has the 
potential to perform better than your proposed system so would be worth 

Cheers,    Steve   K7LXC

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