Do you live in an area that requires a building permit for such things?
If it falls down, will anything get hurt (other than the tower and antenna)?
If the answer to both questions is NO, then you can do pretty much what you
want.
If the answer to either is yes, then you have some figuring to do.
Among the questions you need to ask yourself are:
1) How much wind do you want it to take? (you can look up your county on
several websites and get the required "wind rating")
2) There's some excel spreadsheets around to "rough and ready" calculate the
general level of forces. You could also probably go by "similarity" to
Rohn's data sheets, but see #4 below.
3) Will your concrete base take the forces? (again, you could probably use
similarity to published configurations)
4) Will your tower take the forces (probably... it's short, not too big,
etc.) but, since it's of unknown origin, you'd want to really compare the
sizes and spacings of the structural members against something for which
there is a)published data or b)lots of experience. For instance, there is
some horrible trussing made for mobile DJs that looks a lot like sort of 3/4
sized Rohn 25, but is much thinner members, with longer spans, crummy metal,
and so forth. It's a LOT weaker than it would seem. Fine for holding some
spotlights and a disco ball 10 feet off the ground on a 10 foot span
(and,hey, you'd have a hard time suing the mfr in China anyway) On the other
hand, if the dimensions of your tower sections (the vertical tubes, the
cross members, etc.) are pretty close to the Rohn stuff, and you're not
loading it to within a gnat's eyelash of failure, you're probably good to
go.
If you've gone through the above exercises, you'll know what sort of pullout
forces will be on your anchors, and then you can make a decision about
whether they're strong enough.
Figure it this way... you're going to spend 40-50 hours on the project
(either directly with your own strong back, or earning the money to pay
someone else to do the work). Spending 4-5 hours to make sure it won't
fall down and hurt someone is probably worthwhile.
There's a website (which escapes my mind right now) which has a nice FAQ on
all this stuff around. A huge text file with strengths of guys, types of
towers, etc.
Here's an extremely interesting site:
http://k7nv.com/notebook/towerstudy/towerstudy1.html which does some
interesting modeling looking at the differences in stresses when you use
steel and plastic(Phillystran,aramid, Kevlar, etc.) guys. they may be
strong, but they stretch a lot more, and if the base is rigidly fixed, you
might be in trouble.
----- Original Message -----
From: "Joe Barr" <k1gpl@ham4linux.org>
To: <towertalk@contesting.com>
Sent: Wednesday, April 20, 2005 4:51 PM
Subject: Re: [TowerTalk] Earth Anchors
> On Wed, 2005-04-20 at 12:23 -0700, GALE STEWARD wrote:
> > Ran across this on the web. Thought it might be of
> > interest. Looks like just the thing for FD guying FD
> > antennas.
> >
> > http://www.americanea.com/sanchor.html
> >
> > 73, Stew K3ND
>
> I am in the process of putting together a baby tower. It's four sections,
> 40 feet tall. Each section weighs about 40 lbs. It closely resembles a
> Rohn 25. But it's not a Rohn. I don't know who the manufacturer is. I
> bought it from a gentlemen who bought it in an estate sale.
>
> The top plate includes eye-rings for guy lines. Based on my reading of
> the list the past week or two, I am planning on using Phillystran for
> the guy lines, with the last 10 feet of each being wire cable, including
> a turnbuckle. I'll have PVC pipe covering most of that 10 feet for
> visibility.
>
> A welder is fabricating a foldover hinged base for me, more similar to
> what I've seen US Tower foldover drawings than in the Rohn hinged
> baseplate. The baseplate will be set atop a 4x3x3 concrete base. I'll
> add a worm-gear winch for raising and lowering the tower later.
>
> I'm getting a 14 foot 2" steel mast and a Ham IV rotar. My plans call
> for a single beam to sit on top of it all, a Force 12 C4S.
>
> After I mentioned that the earth anchors looked good for my little
> tower, I got a couple of notes saying that might not be a good idea. So
> I decided to describe as completely as possible what I am planning, and
> ask the list for advice not just on the anchors, but for any part of the
> plan.
>
> I'm a newbie. I got my ticket early in March. As I mentioned on my
> blog recently, I'm not stupid, but I am often under-Elmered. So if you
> have input, please let me hear it.
>
> Thanks,
> Joe Barr
>
>
>
>
> --
> K1GPL / FISTS #11407
> Free software and Amateur Radio
> http://www.ham4linux.org
>
> _______________________________________________
>
> 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.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
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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