List readers:
Actually you can put the guys where you want within reason. You just have to
account for the increased force developed in the guy as you move the anchor
point closer to the tower base. If you increase the distance from the 80%
point the force developed in the guy gets smaller. In each case the vertical
component either gets larger or smaller since the horizontal component
equals the horizontal force acting on the guy. (See the attached *.gif from
my Wind Load presentation).
In the case of going from 80% to 50% the force in the guy increases by a
factor of 1.4 over the 80% force and the vertical component in the tower
from the guy increases by a factor of 1.6 over the 80% force. So if you
account for these load increases in the tower and its foundation for
allowable compression load and in the guy for the increased tension load
then you should be ok.
Remember when straying from the manufacturer's recommendations you are on
your own or get professional help.
73 Hank
Hank Lonberg, P.E. / KR7X
Beaverton, OR USA
Kr7x@arrl.net <mailto:Kr7x@arrl.net>
Hank.Lonberg@harrisgrp.com <mailto:Hank.Lonberg@harrisgrp.com>
Team Pantelleria - IH9P - African Italy - CQWW DX SSB
http://www.qsl.net/ih9p/
<http://www.fortunecity.com/skyscraper/eudora/126/ih9p.html>
-----Original Message-----
From: David Gilbert [SMTP:davidg@primenet.com]
Sent: Thursday, November 18, 1999 5:07 AM
To: K7LXC@aol.com; zippy@sunsetd.com; towertalk@contesting.com
Subject: Re: [TowerTalk] Rohn 25 guy radius oddness.. 80% vs
50%?
Hi, Steve.
For the same guy tension, a 50% radius will put a greater downward
force on
the tower (equivalent to a heavier antenna if you neglect wind
loading) and
it will provide less lateral force along the length of the tower to
keep it
from deflecting in the wind. The 80% radius makes for longer guys,
though,
so any effect of stretching in the guys would be a bit greater, I
suppose.
I'm not saying 50% isn't sufficient in any specific case, but I
think
geometry favors the 80% radius overall.
73,
Dave AB7E
At 07:11 AM 11/18/99 EST, K7LXC@aol.com wrote:
>
> 50% anchor radius or 80% anchor radius - they're just
different
>scenarios. You could have 30% or 120% too or anything inbetween. I
don't
know
>the engineering reason for the difference but as you pointed out,
the 50%
>distance is for another application and not typical antenna
installation
that
>we're used to seeing.
>
>Cheers, Steve K7LXC
>Tower Tech
>
--
FAQ on WWW:
http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|