I'm trying to figure out why you want a separate 2 el 40M beam when the
SteppIR DB-18 already has 2 el on 40M.
73,
Clay W7CE
----- Original Message -----
From: "Grant Saviers" <grants2@pacbell.net>
To: <towertalk@contesting.com>
Sent: Monday, March 29, 2010 9:14 PM
Subject: [TowerTalk] Crank up tower with a stack?
> 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.
>
> 73's
>
> Grant, KZ1W
>
>
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