I have made some bushings by cutting hacksaw slots lengthwise on short
pieces of tubing and squeezing it together to insert. I picked up a beam
from the estate of W7BUD which had a piece of 3 inch irrigation tubing about
4 feet long, slit lengthwise and inserted into a longer piece of the same
tubing to strengthen it. This also works well for splicing 2 pieces of
identical tubing together. BUD put some grease on the slotted piece to help
shoving it into place. I suspect he used a piece of wood and a hammer to
drive it into place. He used a sheet metal screw or 2 to keep it in
73, Dan, N5AR
[mailto:firstname.lastname@example.org]On Behalf Of Red Haines
Sent: Saturday, December 01, 2007 11:10 AM
To: WA3GIN; TowerTalk
Subject: Re: [TowerTalk] Irrigation pipe vertical
I make the bushings from a piece of 3" aluminum tubing with 1/2" wall
thickness. I cut off about a 1" length for each bushing. I turn one
bushing for a sliding fit outside the 2" pipe. That bushing is fastened
with screws to the inside of a 3" pipe at the top, after inserting the
2" pipe with a bushing on its bottom. The bushing for the bottom of the
2" pipe is turned for a sliding fit inside the 3" pipe and is fastened
with screws to the 2" pipe.
Sorry, I don't have any photos. I built all these before I'd even heard
of digital cameras.
By the way, I don't recommend anything longer than a 30' 3" aluminum
pipe for a permanent antenna; it may fail in the wind. A better
combination is a shorter length of 3" pipe supporting a section of 2"
pipe supporting a section of 1" pipe.
Guying the thin irrigation pipe will impose downward force and may lead
to a slender column mode of failure. The guys must be attached to
minimize bowing in a wind.
The aluminum irrigation pipe is not seamless; it is welded. The
material is of modest strength, not up to the standards of material used
in many commercial antennas. Though I've used these as base antennas, I
must recommend caution regarding their susceptibility to failure in
strong wind. Place then where no harm is done if they fail.
At one time, I calculated the permissible wind and the optimum guy
points for such antennas, but I don't have those figures readily
available. Perhaps someone will look up the material specs and repeat
the appropriate calculations for the group. I might do that if I get a
round tuit someday.
73 de Red, WOØW
> I'd love to see some pics of your antennas. I'm thinking of building
> a 4 square for a salt march on my property. I'm particularly
> interested in the bushing as that would be very slick.
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