[TowerTalk] Irrigation pipe vertical

Red Haines redhaines at acegroup.cc
Sat Dec 1 14:10:01 EST 2007

Hi, Dave;

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

WA3GIN wrote:

> Red,
> 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.
> 73,
> dave
> wa3gin

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