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Re: [TowerTalk] HDBX 48 Rohn

To: towertalk@contesting.com
Subject: Re: [TowerTalk] HDBX 48 Rohn
From: "larryjspammenot@teleport.com" <larryj@teleport.com>
Reply-to: "larryjspammenot@teleport.com" <larryj@teleport.com>
Date: Mon, 14 May 2007 17:14:59 -0700 (GMT-07:00)
List-post: <mailto:towertalk@contesting.com>
The HDBX48 that I saw that didn't survive had a 6-element TH6DXX tribander on 
it. After climbing both 80' of Guyed Rohn 25 (with a Telrex 6-element TB6EM on 
it) and the HDBX48, I'll take the guyed tower any day!

YMMV....

LJ



-----Original Message-----
>From: jacobsen_5@msn.com
>Sent: May 14, 2007 4:47 PM
>To: larryj@teleport.com
>Cc: towertalk <towertalk@contesting.com>
>Subject: Re: [TowerTalk] HDBX 48 Rohn
>
>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
>
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