Something I need to point out here.
Although the math is correct, elevated guys *usually* end up derating the
system, not adding to it's capabilities.
> Think geometry, think triangles....
>
> For space restricted installations, with or without antennas on sidemounts
> or ring rotators,
> if you ELEVATE the guy points above ground, you DECREASE the angle of the
> hypotenuse of the triangle formed between the tower/ground and the guy
wire
> between the elevated guy point and the tower.
>
You also add to the leverage being applied to the guy anchor which is at
ground level, or slightly below. That reduces the stability of the anchor.
In other words, instad of a straight pull, you are now pulling on that point
with a lever.
With my guys anchored at 10 feet, with a side pull -- One guy line at 30
degrees, 400# tension, one at 40 degrees, 400# tension, and one at 50
degrees 600# tension. It's been along time since I calculated the angles
and resultang horizontal pull, but I believe it was on the order of 600#.
That is 600# multiplied by 10 feet, or 6,000 ft lbs of torquue being applied
to the guy anchor center of mass.
In actuality, I have the top guy line tied to the base of the post as it
clears the driveway due to the steep angle while the others had to be
raised. That makes the top guy line cross the others, but they are off set
by 4 inches and do not come close to touching due to the tension.
> What does this mean?
>
> It means that you can either rotate a LONGER BOOM antenna than before at
the
> same tower height and STILL clear the guy wires, OR, you can put the same
> antenna HIGHER on the tower and still clear the guy wires.
>
It's been my experience that due to the less rigid guys (unless the post is
back guyed) the system can not be as large as one tied directly to the
concrete at ground level.
> In my case, at my qth, this would be a SIGNIFICANT advantage as my towers
> are very space challenged and my guy wires are shorter than I would have
> liked to have them for sidemount purposes. (they are still within Rohn
specs
> though!).
In this case it's a definate advantage and the reason I elevated mine. To
clear the driveway and the house roof in one direction.
>
> At other qth's with lots of open space, this is not a serious
consideration.
>
> However, the IBeam installation method, if done right, is far sturdier and
> much more flexible than using standard earth anchors in the ground with
lots
> of concrete.
>
This is not the conclusion the engineers came to with mine.
Although the math does show them to be stronger *until* the leverage on the
base of the guy anchor is taken into account. It's the reason I have some
photos of 5" steel pipe having moved out of line by over 2 feet in about 15
years. Now were those same pipes "back guyed" they'd have never moved and
the elevated anchor popints would have been stronger.
Without back guying I had to rely on the mass of 2 1/2 yards of concrete
about 5 1/2 feet deep.
http://www.rogerhalstead.com/ham_files/tower.htm 4 th line of photos from
the top.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com
> It is probably also cheaper depending on the sources of your materials and
> the level of your skills in basic construction.
>
> 73
> Bob KQ2M
>
>
> ----- Original Message -----
> From: "Jack Berry" <jlberry@direcway.com>
> To: "Dan Levin" <djl@andlev.com>; <towertalk@contesting.com>
> Sent: Wednesday, March 03, 2004 8:34 AM
> Subject: RE: [TowerTalk] Re: Elevated Guy Anchors
>
>
> > Okay, I looked over the digest Dan. I can't think of a reason to spend
all
> > that time, effort & money to get guy anchor points above ground. What
> drives
> > that decision?
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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