Cqtestk4xs@aol.com wrote:
>
> In a message dated 8/31/2009 10:17:31 PM Greenwich Standard Time,
> jimlux@earthlink.net writes:
>
> Nothing says you have to tension the cable to a particular fraction of
> it's breaking strength.
Except both the tower makers and the guy makers. Both say to tension
them to 10% of breaking strength. They do that for a reason. If you do
not follow the manufacturer's specifications you open up for a number of
side effects such as resonances and a tower not as "firm" when you are
up there. Will the "Big Grip" ends establish as good a grip at less
initial pull? ROHN specifies 3/16" tensioned to 400#, so the equivalent
Phillystran would be the 4000# test cable.
Yes it's true you do not have a weight of EHS or the massive catenary.
There is so little catenary in the 4000 and 6000# test Phillystran you
really have to look to see it when sighting down the cable. However that
means the guys are less likely to be able to cushion shock. I was once
at 90 feet on a small tower guyed at 3 levels with 3/16" EHS. Someone
ran into the guy anchor with a small tractor. I was hooked on, but I
ended up with both arms and legs wrapped right around that sucker. I had
been up that tower on some pretty windy days and it was rick solid, but
that rock solid tower suddenly took on a life who's sole purpose seemed
to be trying to throw me as far as it could. It's not a weaving, but
rather a series of abrupt movements from side to side based on the
resonance of the catenary. With a lighter guy such as Phillystran the
initial shock would have been immediate and the frequency much higher
(period much shorter), but I don't know about the amplitude. Based on
the physics I would expect the initial shock would have been worse, but
would have rapidly dampened out. Which is safer? I don't know and I do
not want to repeat the experience with either type of guy.
If you are putting up a little 40 footer with a small tribander of
vertical on top, you can get away with ignoring a lot of the rules and
quite often without problems, but the larger the antenna, the taller the
tower, and the more expense that *might* be required of your insurance
company the less you can ignore the manufacturers specs.
On top of this is liability which I suppose I should put in all caps, but
When I purchased the guys for my tower (100' 45G) I used the 5/16, or
6600# test, the 6600 at a 60 degree angle with the top three guys (10%
tension = 660# each) presents a downward force of just over 1700#. IOW
just over 80% of the tension shows up as a downward force. The middle
guys are at 45 degrees and 4400# test with the bottom set also being
4400 . Once before I posted the angles and tension with the resulting
down force for the system, but don't have the ambition to do it again at
the moment.
> It's more a matter of the desired tension for
> appropriate stability for the structure. You could tension million
> pound breaking strength cable to the same few hundred pounds as the the
> regular non-EHS cable.
>
>
Probably not as the tower most likely couldn't support it hanging
straight down.
> I've found that unless you tighten to specs, the tower is "sloppier" and
> has more play.
As have I.
> The sloppiness allows wind gusts to have more of an effect
> on the tower.
>
Amen.
My preference is Phillystran, but you still should be installing EHS (or
wire rope) at the guy anchors to protect the Phillystran from cuts,
kids, tractors, and brush fires.
I prefer the Phillystran because I hang many wire antennas on the side
that would be affected by using conductive guys.
73
Roger (K8RI)
>
>
And cause more wear/fatigue.
> Again, the prime directive is in effect here. I believe the Rohn book
> calls for specified tensioning.
>
> Bill KH7XS
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