I'm new to the list, so I hope my first action of posting a question
here will be acceptable. first let me intro. myself a little. I'm
Patrick Jankowiak, KD5OEI, and I mess around with big old tube type HF
AM stuff as well as 6M AM and FM, and wanting to do a little ATV. Not so
mainstream but it keeps me off the streets at night. I've had more fun
really just working on the equipment and SWLing with an end fed 40FT
piece of wire, but it's time to put up a decent antenna and get on the
air for real. To that end I have had a 56FT Rohn BX lying around for a
year or so.
It looks like I cannot economically put up my 56FT tower due to
"caliche" being 1-2FT under the soil. For those that don't know, "The
caliche reserves in the Llano Estacado in Texas can be used in the
manufacture of Portland cement; the caliche meets the chemical
composition requirements and has been used as a principal raw material
in Portland cement production in at least one Texas plant. Where the
calcium carbonate content is over 80 %, caliche can also be fired and
used as a source of lime in areas, which can then be used for soil
stabilization." I suppose this means I am on concrete for ground.
Anyway, you can't dig into it.
I would like to try putting up 40-50FT of Rohn 25 on a sturdy base and
guy it. The space is limited, so a combination of guying and a strong
base should work well, rather than just one or the other
So far, the plan seems to be to dig down 2 FT to the caliche making a
4x4 hole, use a 2" or 3" rock drill to make a pattern of holes 4FT
further deep in this hole, and set pieces of 1/2" or 3/4" rebar in the
holes, then attach them to the cage of rebar in the 4x4x3 foundation
area which will rest on the caliche rock. The foundation will be made 1
FT higher than the ground around it using a form. In the middle of this
will be set the base section of the Rohn 25. The tower+base section will
not be grounded through this rebar, but will later be grounded
separately. This foundation is not quite enough by itself to completely
secure the tower for the long term. Three guy pipes with two sets of guy
cables will be used.
Since this will be done in an enclosed area of yard that is only 40x40
FT, the three guy pipes will be placed so that they are sunk 5 FT into
the ground and extend 5 FT above the ground. We want to use 4" oil well
drill pipe for this. We can find the pipe because any piece with a crack
has to be discarded and they go to scrap. They are made of chrome moly
steel. I am not concerned about anyone wringing their neck on the guys
inside my 8 FT fence. It is only me and my brother here. The closest guy
pipe will be 20FT from the tower base, and the farthest one will be
28FT. This is OK for the tower's first guy at 25FT height, since the
angle of the lowest guys will be about 40-45 degrees. The angle will be
quite smaller as the tower becomes taller. I may have to limit the height.
These are the tenative plans. I don't know how good the plans are, or not.
What experiences do you guys have with odd/compact tower installations,
especially with guys, guy posts, and the angles of guy wires versus the
stresses on them? Obviously I can reduce the angle if I strengthen the
guy, up to a point, but beyond that it is of no further merit and the
tower cannot be made higher safely.
Is there a free downloadable calculator to help with the angles of the
guys and design of the site? All advice will be welcome.
As far as what will go on the tower, I want to put up a stack of simple
and light weight 6M, 2M, 440 beams on the top (no HF beams), and then a
bit lower, have an outrigger for a couple of small VHF and UHF discones
for my FAA gear and the support for the center of a 100FT dipole for HF.
I think that should be more than adequate to have a real nice station.
Thanks in advance for any constructive comments,
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