> 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.
Like many things, it depends on what you use for materials and how solid the
structure is
and how well anchored in the ground it is.
> > 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.
It has been a long time since I did physics calculations so I will pass on
doing the math.
One of the more learned towertalk readers can do the calcs.
The crux of the matter is that with ONE galvanized steel guy anchor, prone
to rusting, everything depends on the state of that one piece of steel
pointing into the cement.
With a set of heavy Ibeams, many feet long, many feet high and many feet
into the ground into concrete, and with a vastly heavier mass, if it is
built correctly and bolted together correctly, you have a far sturdier
structure for guying. Please understand that I am NOT talking about using
ONE Ibeam mounted vertically, I am talking about using SEVERAL Ibeams bolted
together to form an Inverted TEE, mounted about 3'-5' deep into the cement
in a trench about 8'-10' wide. There is NO comparison to a single
galvanized steel anchor.
You can ask W3EA for details on his installation which is as sturdy as it is
visually pleasing to look at!
> 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.
Totally unnecessary with the installation that I described.
> > 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.
Again, you have to do the math with the materials actually being used in the
configuration actually used.
>
> 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
73
Bob KQ2M
_______________________________________________
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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