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[TowerTalk] An Engineering Question

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Subject: [TowerTalk] An Engineering Question
From: (David Clemons)
Date: Tue, 27 May 1997 16:42:43 -0400 (EDT)

        I have a question concerning guy wire anchor placement.  I have
two towers (one is 83 feet of Rohn 25 with a Hygain 155BA and 105BA, the
other is 99 feet of Rohn 45 with Cushcraft 204-CD and 402-CD.)  A recent
edition of the ARRL handbook says that the anchor distance should be
between 60% and 80% of the tower height.  I have two anchors on each leg,
with the lower two sets of guys on the inside anchor and the highest guy
alone on the outside anchor.

        Now the problem - the 13 acres of property behind me was bought
last year and the new owners are putting up horse corrals for their
boarding/training business.  We recently discovered that four of my guy
anchors (both anchors on one leg of each tower) are actually on their
property.  They have been nice enough to tell me it's ok, but two of them
actually fall inside one of the corrals and I think it best to get them
out of there.  I am not going to move the towers, so that means I have to
put the anchors closer (the outer ones by 12 feet or so) and also
probably shorten the towers somewhat.

        The underlying question really is "how much can I cheat on the
angle of the guy wires?".  Now there are those among you who will
correctly tell me that any cheating is dangerous, and I understand that
concept.  However, I am also aware that there is a different amount of
danger associated with the anchor at 59% of the tower height than at 39%
or 29%.  Also, my use of two anchors takes some strain off the anchor for
the top guys - thus making the issue of the strain on the wire and tower
legs more likely to be the critical problem.  The guy wire is 1/4 EHS,
which I believe is rated for 6600 pounds.  The wires are broken up with
insulators, and some of the wires are fastened with deadends while other
connections are made using 3 cable clamps on each side.  (If it mattered,
I could replace all cable clamps with deadends.)

        Does anyone have any experience or idea of the reliability of an
installation with the top anchor at 50% of the tower height?  How about
as little as 40% (about 68% angle to the ground)?

73, Dave Clemons K1VUT

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