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[TowerTalk] An Engineering Question

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Subject: [TowerTalk] An Engineering Question
From: (Paul D. Schrader)
Date: Thu, 29 May 1997 18:02:12 -0400

I once had a Rohn 45 at 115 ft with large beams at 116 and 125 ft.  It had
guy anchors at 25, 30, and 35 ft from the tower; the top guys tied to the
35 ft out anchors.

The key is to have enough guys, strong enough anchors, strong enough
wire, and strong enough tower.  There is nothing magic about how far out
the guy wires are.

I had three qualified people check the calculations.  Me (I'm an E.E. P.E.),
a Mechanical P.E., and the factory guy.

It stayed up through some big winds and ice storms etc. until I took it down in
1973 to move.  There was a picture of of it with the ARRL DX phone contest
results in QST in the sixties with my old call W4BCV.

If it had fallen it would have taken out 3 houses.  A neighbor called the zoning
commission who came out to inspect it.  There was no zoning restriction and he
looked at it carefully and told me it was the finest tower installation he
had ever
seen.  (It was in a subdivision.)

Things can be done different than the norm if you know what you are doing.  If
you don't know, find someone (or hire someone) who does.  Or don't do it!

I hope this has been of some help.

                        73  Paul N4XM

At 16:42 5/27/97 -0400, you wrote:
>        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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