Hey Jim,
Congratulations on your very good education. I hope it has served you well.
I too have a very good education but what is more important to me about the
current topic is good old experience. I am one of those professional tower
installers but not like the one you hired to do your work. "Too unstable to
climb more than 25 ft above a guy", I don't think so. I have installed 46
ham radio towers in my long career including the five I currently have at my
station. I can only think of 7 of the 46 that we used concrete in the base
and I am very happy to say that only one of those towers has fallen. That
one came down in a tornado and it had concrete in the base.
I am , of course, talking about guyed towers. Rohn 25, 45 and 55 up to 200
feet. Free standing towers must have a concrete foundation.
When I talk to young Hams that are thinking about a tower, the first thing
most say is " I don't have much money for this". I recently installed a 70
foot Rohn 25G with a tri band Yagi, a rotor, rotor cable, feed line and guys
for a young man with a young family. We got the tower just for the cost of
taking it down. Everything else was used and some things came from a
hamfest bone yard. Total cost including my labor for taking the tower down
and back up with two sets of guys, antenna and everything was $555.00. He
is now a happy ham and thrilled at every new DX contact he gets in his log.
I could go on and on about how much of the "published recommendations" you
referred to are written by lawyers and not engineers but I have likely said
too much already. I don't intend to ruffle feathers here. Your big "FALSE"
just got me started.
Cheers,
Dave - K4SSU
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "Tower Talk List" <towertalk@contesting.com>
Sent: Sunday, August 23, 2009 12:49 PM
Subject: Re: [TowerTalk] Amount of concrete in ground for Rohn 45G
> On Sat, 22 Aug 2009 23:19:05 -0400, Dave Johnson wrote:
>
>>In your post you included "guy wires" so that makes me think you are
>>talking
>>about putting up a guyed tower. If so, you don't really need any
>>concrete.
>
> FALSE! This statement is as silly as the 3:1 mass "rule of thumb" that the
> previous poster asked about. I'm an EE, not an ME, but I went through the
> University of Cincinnati at a time when we had to study some fundamental
> ME
> courses as part of my basic EE course.
>
> A tower must remain solidly in place in the presence of some rather
> significant forces imposed by mother nature, as well as the weight of the
> antennas, mast, other hardware, and a climber. Wind at the top of a tower
> gets multiplied by a rather substantial bending moment at the bottom of a
> tower, and forces applied at various heights create other forces at other
> parts of the tower. Anchoring the tower base rigidly in place, and
> anchoring
> multiple points along the tower with guy wires, minimizes these bending
> moments and makes it more likely that the tower (and the climber) survive
> those forces.
>
> Having a tower fall is not good. Depending on what it is, what it holds,
> and
> where it is, it can break things on the ground, hurt people on the ground,
> even kill them. And at the very least, it will probably break your antenna
> and the tower itself. Any one of these things can significantly lighten
> your
> bank account, threaten your retirement, even make you homeless.
>
> My tower is in 1 cu yd of concrete. I'm far too old and out of shape to
> climb
> it, so I hired an experienced climber to help me build it and put the
> antenna
> on it. We guyed it as we built it, at intervals of 30 ft (recommended by
> Rohn
> for the 120 ft ht we built). He reported that the tower felt too unstable
> to
> climb more than about 25 ft above the highest attached guy wires, and
> would
> not climb above them until the next higher set was attached. And this was
> with virtually no wind, the only forces on the tower being his weight on
> one
> side of it.
>
> I recall the calculations to assess the relative safety of a tower as
> being
> rather complex. (In case you haven't noticed, Mother Nature causes winds
> to
> do some rather interesting things at times, and in some parts of the
> world,
> the earth occasionally shakes.) If you're not equipped to perform them,
> you
> should either accept the published recommendations of the tower
> manufacturer
> or hire a competent ME to do them for you. Some of the standards for which
> these computations are done are based on local building codes, and carry
> the
> force of law.
>
> BTW -- someone recently asked about the cost of a tower. Since I just
> finished my installation, I totalled the costs. I figure that buying a
> 3-el
> SteppIR, securely installing it at 120 ft, feeding it, running control
> lines
> for the antenna and rotor, and properly building the tower cost me just
> over
> $9,000. I bought all of the Rohn 25 pieces used, as well as the hard line.
> Most of the rest of it had to be bought new -- guy wire, turnbuckles, guy
> hardware, guy anchors, rotor, control cable, rated coupling hardware for
> the
> guys, etc. That cost includes $1,700 for labor to do the climbing and help
> me
> mix and pour the concrete. Roughly $500 of that cost is the additional
> costs
> because the tower is about 280 ft from my shack. Cost was reduced because
> I
> did not have to pour concrete for guy anchors -- instead I used big lag
> screws into the bases of giant redwoods that surround the antenna on all
> sides, one screw for each guy wire (that is, 12 screws).
>
> 73,
>
> Jim K9YC
>
>
> _______________________________________________
>
>
>
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