One point I forgot to make. The two bracket attach points to the house
are usually reinforced on the inside. In a strong wind there is a lot
of stress on these attach points. With 15' of tower and mast above the
top bracket at 30' and the bottom bracket at 15 to 20 feet (what ever
ROHN says) I would think a small 3 element tribander should work, BUT,
I'd ask an engineer about stress on that wall.
I'd have more concern about the wall than the tower. A good strong wind
night crack plaster on the inside...or worse, so be sure to check with
an engineer. Bracketing to a house wall isn't nearly as simple as it
sounds. Many have done it successfully but many also reinforced those
walls. There was an article in QST on this topic a few years ago and it
contained a few cautions as well as to how to reinforce walls to bracket
towers.
73
Roger (K8RI)
On 5/5/2016 Thursday 12:08 PM, Rob Matherly wrote:
A couple weeks ago I asked about self-supporting a 40' Rohn 25 tower.
After input from the list and a no-vote from the Missus on guy wires strung
across the yard, I've gone back to my original plan to house bracket it. I
have a two-story with 10' ceilings, so there's plenty of house to hold it
up. (There is some concern regarding my metal roof, but less than I'd have
to deal with if I were to anchor a guy wire in a flower bed.)
Question #1 - I've read at various sources that I can go 16' above the
bracket. Is this correct? Assuming my rough estimations of the house
height are correct, my top bracket will be at about 30'. I will also have
a bracket in the 15' area. I should be safe with about 45' of total height
including my mast f I understand the Rohn data correctly. Let me know if
this is incorrect, please! I will also be sistering the studs to help
spread the weight out a bit.
Question #2 - I'm going to homebrew the house brackets since I have the
equipment and know-how to build it correctly (and not some hobbled-together
mess of metal.) Does anyone here have dimensions and specs on the
materials used? I believe the angled pieces are 2x2x3/16 galvanized, but I
am not 100% on that. I do not have any information on the thickness of the
flat steel.
Question #3 - It is my understanding that, since it is bracketed to the
house, the concrete base does not need to be as large - 2x2x3 as opposed to
3x3x3. Is this correct? I don't want ground heave to damage my house.
Thanks again, folks!
Rob, w0jrm
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73
Roger (K8RI)
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