[TowerTalk] FW: Guy article in CQ
K1TTT at ARRL.NET
Fri Jan 15 15:09:44 PST 2010
Ah, but if you have asymmetric guys, which ones do you put the gauge on?
Here are some things to consider.
The key is that when the tower is vertical the horizontal force from all the
guy wires HAS to be equal. If it weren't then the tower would be moving!
So the objectives are 2 things... first, to have the tower vertical.
Second, not to exceed manufacturer specs on tower or guy wire forces.
If all the guy wires are the same it is obvious that you only have to
measure the tension on one set of guy wires and the others have to be the
same if the tower is vertical. But if the guy wires are at different angles
to the tower the ones that are closer to the tower will have higher tension
than the ones farther out(it goes as the cosine of the angle between the guy
and the tower, or the sine of the angle from the ground to the guy wire).
So as you pull a guy wire farther out from the tower the tension in it has
to decrease to keep the tower vertical.
Now the question is, which one do you measure? Personally I would recommend
measuring the tension on the one that is anchored closest to the tower since
this one would have the highest tension. This will result in lower than
recommended tensions in the other guy wires which will make them look/feel
loose. If the farther out ones are much farther out than the others there
may be problems with movement in the wind because it will have more slack to
be taken up. This is one of the reasons that rohn specifies limits on guy
locations, if you go outside their limits you should have the design
evaluated by an engineer... there may be other options, like changing the
guy wire type, elevated anchors, using 4 anchors instead of 3, or other
configurations to equalize the anchoring.
David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: Roger (K8RI) [mailto:K8RI-on-TowerTalk at tm.net]
> Sent: Friday, January 15, 2010 22:46
> To: Tower and HF antenna construction topics.
> Cc: 'N1MM'
> Subject: Re: [TowerTalk] FW: Guy article in CQ
> Rex Lint wrote:
> > Tom, et. al.,
> > A couple of field days ago we put up a tower with one of the anchors
> > reeeeaaaalll far away: they guys on this side were very long.
> > When we tightened all the guys, the long ones were "looser" then the
> I think someone was confusing the catenary (sag) with tension.
> > - they sagged like crazy. But, we cranked away with the come-along, and
> > finally the tower BENT OVER at the lower guy point.
> That is because too much tension was put on the longer guys. With the
> same tension the longer guys will have much greater sag in this case.
> > Out take-away was, "Keep all sets of guys symmetric."
> Although it is a good idea to keep guys symetrical this was not a case
> of asymmetrical guys, but some one assuming the longer guys weren't
> tight enough. In cases like this it should have been obvious that even
> with the extra sag the effort to use the come along would have indicated
> the guys were under plenty of tension. When ever pulling like that use
> a tension gage.
> Roger (K8RI)
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