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[TowerTalk] Crank up tower with a stack?

Subject: [TowerTalk] Crank up tower with a stack?
From: Grant Saviers <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Mon, 29 Mar 2010 21:14:16 -0700
List-post: <">>
As a feasibility check, here is a potential design:

I'd like at least a 2 x tribander stack (10 sq ft ea, e.g. TH7DX or 
SteppIR DB-18) and a 2 el 40m beam (various) on a crank up/tilt over 
tower, height to the top of 80' or so.  This doesn't work per the off 
the shelf tower catalogs but I think can be made to work for 70mph 
ratings and wonder if others have attempted to do so.  I think it takes 
about 25' of separation of the tribanders with the 40m in between, which 
by my calculations is possible with 10' of 2.75" od of 4140 DOM .250" 
wall tube stepped to 20' 2.25" od x .25" wall and a custom made thrust 
bearing, rotator tbd.  So that part seems feasible, obviously so, since 
many stacks already exist on fixed towers.

For the tower, my thoughts are use an 88' crank up HD tower such as the 
US Tower HDX-588 without the top two sections.  The logic is the wind 
load and moments from the top two sections plus its rated top wind load 
are probably larger than the mast and beams.  This is an estimate and 
would need to be calculated.  The masts plus antennas are about 400 lbs 
of dead load which may be on the high side versus the weight of the two 
sections plus rated antenna.

Any one tried this?  Any suggestions on where to find tower data for the 
calculations needed?

As to why this approach - codes here are auto approval to 80', I'm tired 
of climbing, the SteppIR forum recommends easy maintenance, guys are a 
problem in pastures, and my ridge top QTH doesn't need much in the way 
of tower height.


Grant, KZ1W


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