The concern about the irrigation pipe should be its breaking strength as
a composite structure. The concrete has low tensile strength and
without reinforcement in addition to the very thin Al tube, I doubt will
survive. Maybe a fiber reinforced concrete will add enough tensile
strength, who knows? Save your pipe for making a vertical on top of the
barn, arena, stable, etc. where you can guy it. With elevated radials
it makes a terrific antenna.
I have 4 telephone poles planted about 4' holding antennas, two for a
360' long dipole across a gulch, another with a A4S beam, another had a
GAP vertical. I did put guys on the A4s pole since I climb that one.
The others haven't moved, dug with a tractor 18" PTO auger and hand
tamped, in the horse pasture. Your tension in the loop shouldn't be
more than about 70# per leg so is not likely to move a pole much. If
they do tilt pull them upright with the tractor and put a diagonal brace
on the inside from a 15' piece of pole. Use some steel brackets or
all-thread to hold them together.
Unfortunately, PG&E now cuts all used poles into dumpster sized pieces
at removal so used ones over 12' long are hard to get .:-(
As to other "inexpensive options", steel pipe or square tube (better)
would work. A 20' 4x4x3/16" plus 20' 3.5x3.5x1/4" welded with about 1'
of overlap might show a little bend but will be strong enough according
to my ranch/experience calibrated guess. YMMV or get some calcs done.
about $400 new per pole, cheaper if from a scrapper.
Grant KZ1W
On 2/5/2011 3:06 PM, J. Dolson wrote:
> Dear Gentlemen,
>
> I've googled and checked the TowerTalk archives but have been unable to find
> and answer to this question.
>
> I would like to put up a square 80m horizontal loop at a height of about 35
> feet.
>
> ENVIRONMENT AROUND THE ANTENNA:
>
> 1. Because of horseback riding on the property, I am unable to use guy
> wires, therefore the four towers supporting the loop must be free-standing.
> 2. There are no trees or other supports in the field.
> 3. The soil is heavy clay.
> 4. Maximum wind gusts during the past ten years have been 65 mph.
> 5. The only times that people are in the field are for horseback riding and
> mowing.
>
> QUESTIONS:
>
> 1. I have several 40 foot lengths of 4" diameter aluminum irrigation pipe.
> If they were to be filled with cement and dropped five feet into the ground
> would it be stiff enough to stay vertical?
>
> 2. If that is not feasible, then could I fill say a 15 foot length of pipe
> with cement, drop it 5 feet into the ground, and attach a guy wire to the
> top of the pipe? That would put the guy wire up ten feet and away from the
> horses. The disadvantage of this is that I now have eight obstacles in the
> field for the horses to avoid instead of four.
>
> 3. If idea of using the 40 foot irrigation pipes is dumb, then are there any
> other inexpensive tower options other than phone poles (phone poles are
> currently Plan B).
>
> Thank you for your consideration.
>
> Jim Dolson, K8DDV
> Grand Rapids, MI
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|