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!
>Sent: May 14, 2007 4:47 PM
>Cc: towertalk <email@example.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
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