[TowerTalk] Stacking Beams

[Timothy Coker]

I have the exact same setup that you have with the exception that I
converted my XM240 into a D40 (just used driven element) due to the fact
that my mast is an unknown steel of 2"OD and .125" walls ten feet in length.
Everything is working fine at my qth on 29' of Rohn 25G, using a 30 year old
T2X that my elmer and I rebuilt. As you probably know the Rohn 25G antenna
top has no thrust bearing. I would have put up the XM240 had I had a thicker
mast of atleast DOM 1026 quality.

Antenna  Height above top of Rohn 25G (mast extends down 3' from top of
Rohn)

TH7DXX 0.5'
A3WS w/30m 3.5'
D40 7'

My antenna is mounted parralell with my TH7DX... SWR is under 2:1 where it's
supposed to be as per the manufacturers specifications. As my budget allows
I will be placing the above antennas with the XM240 fully installed on the
top of an LM 354HD using a 22' Cromolly mast 2"OD x .250" walls spaced with
the TH7 at 0.5', A3WS w/30m at 8.5', and the XM240 at 17'.

A look at WinMARC shows that you will have a mast with a yield moment of
16748 in-lb at 70mph winds. Typical disclaimers apply here... I have no idea
of the parameters used in developing the software, but it's a starting
point.

The reason I'd put the XM240 at the top is due to the fact that it's
windload rating is only 5.5sq ft vs the TH7's 9.4 sq ft. I'd keep the A3WS
in the middle in order to gain as much seperation, vertically, as possible
between my 15/40m elements.

Droop is not an issue for me using my 7' of mast above the tower.

Send me an email direct if you'd like pictures of my install, etc.

Tim, N6WIN.



On Wed, Apr 14, 2010 at 4:57 PM, Don Tucker <w7wll at arrl.net> wrote:

> Looking for feasibility advice.
>
> Have one tower, a HyGain HG-70HD.
>
> Currently have a 7 el TH7DX tribander right at the tower top with a  3 el
> A3WS duobander 8 feet above it. No noticable interactions.
>
> Have acquired a Cushcraft XM240 2 el shorty forty. Would like to put in on
> the same mast as the latter two.
>
> What is the best placement of the these (bottom, middle and top) and what
> is
> the minimum separation I can get away with between them? E.G., 40 on the
> bottom, the TH7 middle and  12/17 top, or????  Or will this all be too much
> for a single HD mast/TX2 rotator?
>
> Don W7WLL
>
>
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