Towertalk
[Top] [All Lists]

Re: [TowerTalk] Philly installation

To: Cqtestk4xs@aol.com
Subject: Re: [TowerTalk] Philly installation
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
Date: Tue, 01 Sep 2009 00:20:05 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>

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
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>   
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>