[TowerTalk] HDBX 48 Rohn

[jacobsen_5 at msn.com]

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
K9WN  Jake