K1TTT wrote:
> Ah, but if you have asymmetric guys, which ones do you put the gauge on?
> Here are some things to consider.
>
If they are all the same angle they are *basically* symmetrical for both
vertical and horizontal tension. The tension should be the same
regardless of length.
> The key is that when the tower is vertical the horizontal force from all the
> guy wires HAS to be equal.
If you are referring to one tier, that is true, but again if they are
the same angle the tension in both the vertical and horizontal axis will
be the same for each guy regardless of length.
> 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.
Not necessarily. You can get more than a 20% differential between guys
for tension on a 45G. 25G is less susceptible to this than the 45G as
the 25G is far more flexible.
I've found it necessary to go back and fourth between guys with the
tension gage to get them correct. If you take up too much on one side
you can get a rather strange looking tower when looking up the side.
The legs will not be straight.
> But if the guy wires are at different angles
> to the tower the ones that are closer to the tower will have higher tension
>
The guys will have the tension you put on them which is based on the
working strength of the guy. If the guy is rated at 6000# then it should
have 600# tension. The important thing is to keep the angles the same,
not the lengths when the terrain is uneven or sloping. The lengths can
vary quite a bit, but within reason as you have to be aware of creating
low frequency resonances.
> 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?
All of them.
Particularly on a 25G which is far more flexible than the 45G you can
make it look like a pretzel if the guys are not properly tensioned in
careful order. You slowly approach the desired tension by carefully
going back and fourth between the guys a bit at a time while checking to
make sure the legs of the tower are straight. A 100' 25 G guyed at 3
levels can end up with the mid tier of guys as much as 3 or 4 inches out
of plumb (I've seen them worse than that) with the rest of the tower if
care is not given to the guy tensioning. Unfortunately a flexible tower
like the 25G will allow you to pull all guys for a particular tier tight
(to the proper tension) by actually moving the tier out of plumb when
tightening one guy line. Those in particular require approaching the
proper tension slowly and in small steps. Actually you can carefully set
it equal and THEN using the turn buckles increase the tension on each
one by a specific number of turns such as 2 or 3. This works IF the
tower was straight and the tensions were equal to start. Once a tower
gets out of plumb it can be a real bear to get straight and it becomes
quite easy to put a permanent set in the tower. Once the tower takes a
set it'll never be the same.
> 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.
It should have the same tension as all the other guys on that tier. All
guys of the same size/strength should have the same tension regardless
of length.
> This will result in lower than
> recommended tensions in the other guy wires which will make them look/feel
> loose.
No it won't and don't go by looks such as the catenary. the tension gage
is your guide as is the tower remaining straight.
> 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.
No, it shouldn't have more slack if the tension is properly set. It will
have a definitely deeper catenary though which is entirely different. A
deeper catenary does not necessarily mean the guy does not have enough
tension. For two guys of the same length and angle it would indicate
tension, but a longer guy will have a noticeably deeper catenary for the
same tension.
> 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...
The distance from the base of the tower is to confirm where the guy
would be on level ground when all have the same angle.
> there may be other options, like changing the
> guy wire type,
Guys should be of the same type and at the same angle for any given
tier. If the ground slopes up they will be shorter than shown in the
catalog and if it slopes downward they will be longer.
> elevated anchors,
Elevated anchors are not a good idea unless you have no option. I had to
clear a driveway and an elevated anchor, back guyed was the only option
to keep the angle correct.
> using 4 anchors instead of 3,
With 4 point guying the angles still should be the same.
> or other
> configurations to equalize the anchoring.
>
There are only two things that will equalize the anchoring. The guys at
the same angle for the tier and *each* guy tensioned with a gage unless
you bend the tower.
73
Roger (K8RI)
> David Robbins K1TTT
> e-mail: mailto:k1ttt@arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>
>
>
>> -----Original Message-----
>> From: Roger (K8RI) [mailto:K8RI-on-TowerTalk@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
>>>
>> others
>>
>> 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.
>>
>> 73
>>
>> Roger (K8RI)
>>
>> _______________________________________________
>>
>>
>>
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