Hello Larry and all....... Seems several comments have been made on the wind
loading of the Rohn BX/HBX/HDBX self support towers.::
"Rohn Ham Tower Catalog, and for the BX/HBX/HDBX towers, it says:
"NOTE: ANTENNAS DEVELOPING A LARGE TWISTING MOMENT DUE TO WIND MUST NOT BE USED
ON THIS TOWER. ANTENNAS SHOULD BE LIMITED TO THOSE HAVING A MAXIMUM BOOM LENGTH
OF 10 FT."
It rattled my lazy brain a little so I went and dug thru my files.
#1. The above statement is on the page for the BX 64 tower. Rated for 6 sq. ft
of antenna area.
The HDBX is rated for 18 sq feet of area. Think about it. 18 sq ft on
a 10 ft boom. My thoughts are it would take about a 4" boom and lots of LARGE
size elements to get to 18 sq feet of area on a 10 ft boom.
#2. I had an HDBX 40. Put a KT34A on it. (I know, only 6 sq ft of area) 4 els
on a 16 ft boom. No problems in windy Albuquerque.
#3. AND, b4 the flames start I will back up the above 2 statements by
saying::....... I am looking at WET STAMPED figures done by an engineer for a
ham so he could get a permit for construction of an HDBX40. It was designed
with a Hy-Gain 391S at 3 ft above the top plate. Now those of you old enough,
like myself, know that the 391s is TH7DX...... 7 els on a 24 foot boom. 9.4 sq
ft of area. Engineer had a foot note saying the antenna would fail before the
tower. As such he recommended that the boom be tethered to the mast with a 1/2"
nylon rope, 6000 lb breaking strength. Got his permit and was a happy ham.
As always, YMMV. Don't use the above statement to home-engineer your own
tower. If you're not sure about your own installation, play it safe and pay the
$$$$ for a professional calculation. All standard disclaimers are in order
here. I wasn't the engineer. I'm not an engineer. Heck, I can't even spell
engineer. And no, you can't have a copy of the figures.
73 es GD DX
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