Hi all,
I agree with Hank. My first tower was Rohn-25G at 110'. The guys were about 45'
from the base. 6'X8" screw in the ground anchors were used. 5/16 Ga. Power type
guy cable was used with 12" turnbuckles. The tower had 10, 15, and 20M 4el full
size mono-bands in a Christmas tree. The Mast was 2" OD X 3/8" wall thickness.
Many storms and 93mph winds. No problems.
WARNING: The ground here is Ga. red clay and granite. This arrangement will not
work everywhere. Sandy or loose soil might require 90%.
>From a 30 year Ga. Power tower engineer:
Everything matters, but the Guys are the strength of the tower.
If you do not know what you are doing, hire a professional tower man in your
local area.
Many people (HAMS) have died installing towers and pulling them down.
Bill Wall
KC4UZ
Antenna
Mart
"Lonberg, Hank" wrote:
> 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
> >
>
> --
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