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Re: [TowerTalk] Crank up tower with a stack?

Subject: Re: [TowerTalk] Crank up tower with a stack?
Reply-to: "Tower and HF antenna construction topics." <>
Date: Tue, 30 Mar 2010 13:13:40 EDT
List-post: <">>
In a message dated 3/30/2010 9:30:32 A.M. Pacific Daylight Time, writes:

>  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 
calculations needed?
    All you have to do is order what you want from  UST. They'll build you 
anything you want - all you have to do is pay for it.  What you want is 
something like a HDX-688, 788 or similar  configuration. K0SG did that and has 
MonstIR and a 3L F12 80M beam. It's  very brute. They'll work out all the 
calcs and build it per industry  standards. 

Cheers & GL, 
Steve     K7LXC
Professional tower services for hams


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