[TowerTalk] tower specs/not wind loads

[Robert Chudek]

I will confirm what Gene is saying about the BX towers who's cross members are riveted, not welded. In my youthful radio career, I put up 104 ft of HDBX tower. It was 4-way guyed at several levels. I installed a 6 foot torque bar at the top guy point to help reduce the twisting movement in the wind. Periodic inspection revealed rivets that had popped on this tower. As these were discovered I would install 1/4-20 bolts in their place. This tower survived 4 or 5 seasons with a 6-element 15m homebrew yagi on top. Oh, the boom was 2" OD irrigation tubing and was 40' long. (Did I mention I did this installation in my youthful radio career?)

As an aside, our local radio community was fortunate to have a ham operator (WA0MGY - sk) who was our source for inexpensive undisturbed earth anchors. These were really slick... you auger an 8" hole at the proper angle about 8 feet deep, drop the anchor into the hole, use a special tool to expand the head of the anchor into undisturbed earth, and backfill the hole. Later when I removed the tower, I simply unscrewed the above ground head of the anchor and pulled the rod out. You would never know there had been an anchor in that location. I wanted to install elevated guy posts but was (fortunately) elmered away from this type of installation.

Trylon towers are also riveted and I have found rivets that have popped on these towers as well.

I conclude these mechanical failures are a consequence of torsion forces created by the long booms on the antennas we use today.

73 de Bob - K0RC


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Message: 1
Date: Tue, 24 Jan 2006 14:27:12 +0000
From: ersmar at comcast.net
Subject: Re: [TowerTalk] tower specs/not wind loads
To: 
Message-ID:

Mike:

     You're correct - the BX-series of antennas has a torque limit on them.  This is because they are assembled with rivets, not welds, between the cross pieces and between the cross pieces and the legs.  The rule of thumb with these towers is that a ten-foot long boom would impart just about the maximum safe wind-induced torque on the tower.  A longer boom might twist the thing apart.

     Caveat Amateur.

73 de
Gene Smar  AD3F