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[Towertalk] Rohn 25G foundation requirements

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Subject: [Towertalk] Rohn 25G foundation requirements
From: (Bill Coleman)
Date: Tue, 30 Jul 2002 20:12:46 -0400
On 7/29/02 8:20 AM, Mike Morrell at wrote:

>I am going to install an unguyed, free-standing 30' high Rohn 25G tower 
>and wish some information about various foundation requirements.  
>Some info I gleaned from the Rohn website state that I should imbed a 
>short section of 25G in a  4' X 4' X 4' deep block of concrete reinforced 
>with # 7 rebar on a 12" pitch/grid pattern.

Yup. Rohn drawing B870725.

>Others at the local club suggest using the Rohn 25G self supporting  1/2" 
>thick plate that is anchored at  it's  corners with 5/8 " anchor bolts 
>imbedded to a concrete block.

What sort of concrete block?

I'd point out that Rohn 25 really isn't intended to be self-supporting, 
so you are probably better off installing it according to the 
manufacturer's suggestions, rather than improvising.

One point -- if you embed part of a section, you won't get to 30 feet. It 
would be less than that, depending on the type of top section you used. 

>My plans for the tower are as follow:  1) the lightest HAZER system, 2) a 
>CDII rotor and 3) a Mosley Mini 33 triband. 
>The Mosley published loading is 2.5 sq. ft.

I'm not sure what type of sq ft Mosley is using here. Is that flat plate 
equivalent, or is that projected area?

Assuming it is (round) projected area, Rohn rates Rohn 25G a follows in 
self-supporting service:

70 mph - 6.4
80 mph - 3.7
90 mph - 1.7

1/2" Radial ICE
70 mph - 2.5 

So, on the surface, such an installation might be possible, so long as 
your rated wind speed is 70 mph or less, or 80 mph or less, and you don't 
have to contend with ice.

>Any comments about the various foundations and suggestions are appreciated!

One consideration on self-supporting towers -- remember you have to climb 
them. If nothing else, one has to climb them to install the Hazer, no? 
Unsupported Rohn 25 gets uncomfortably wiggly above about 20 feet, in my 

One other thing to consider is to bracket the tower to a structure -- if 
you have a structure close and tall enough to help. Although such a 
structure might interfere with your plan to use a Hazer.


Mike, no offense to you, but I'm really annoyed at these Adelphia guys 
right now. They may cost me a job.

Bill Coleman, AA4LR, PP-ASEL        Mail:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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