Dave Johnson wrote:
> 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've never used a dirt base on any thing that tall, but I have one 25G
(guyed) going to 60 feet with a dirt base.
As I've posted previously I've put up a good many towers using dirt bases.
> 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.
>
BTW even for free standing, I've seen 60 footers without concrete.
They were *some* of the old wind mill towers. They were pretty wide at
the base compared to the height of modern free standing towers, but they
are quite capable of holding a large tribander, or even the Big Mosley
30 through 10 or is it 20-10 with the WARC bands. They used steel
pilings for the bases of the legs. I have no idea as to how deep they
went or whether they were driven in or set in a bored hole. OTOH I've
not seen one in years. I will add that most of the windmill towers I've
seen were set on concrete pilings.
73
Roger (K8RI)
>
> 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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