I built a few telescoping verticals with one section each of 3" and 2"
irrigation pipe. I made aluminum bushings to fit the 2" inside the 3"
and permit them to telescope for transport and to adjust length. One
bushing at the top of the 3" section fits the ID of the 3" and is
fastened with machine screws. The ID of that bushing is slightly larger
than the OD of the 2" pipe. The other bushing, at the bottom of the 2"
pipe, fits the OD of that pipe and is fastened to it. The OD of that
bushing is a sliding fit inside the 3" pipe.
The objective was to telescope the sections, but using the 2" pipe on
top also reduces the wind load on the top portion.
A clamp made of 2" PVC, slit in 4 places with a hacksaw, clamps, with
hose clamps, over the 2" pipe to hold it in the extended position. I
always left 1' to 1.5' minimum overlap of the sections.
To make a 1/4 wavelength on 80 meters, with two 30' lengths of
irrigation pipe, I added a length of 1" aluminum tubing at the top of
the 2' pipe; I just bolted it to the OD of the 2" pipe.
For field day or other portable use, I modified some tripods to clamp
short sections of 3" PVC pipe, with slits for clamping, with hose
clamps, to the 3" pipe. I fastened the tripods to simple frames of
square aluminum tubing. I can raise 41' easily by myself for a 20 meter
5/8. I need one or two persons to hold the base of a 65' mast to the
ground while I walk it upright. For field day or portable use, I put 4
nylon guys at the joint between the 2" and 3" sections.
I have sheets of perforated aluminum about 4' square under the tripods,
with radials bolted to the aluminum sheets with SS hardware to preclude
copper to aluminum contact. The antennas perform well with just the
aluminum sheets, but I usually add 16 or more radials. I put 2 or 3
radials into one crimp-on lug to put then on one bolt quickly.
A 5/8 wavelength 20 meter vertical with radials works well for field
day! It is often necessary to use the attenuator at the rig to prevent
overloading the receiver when bands are crowded.
I never implemented any proper connection between the feedline and the
aluminum mast, because my first hurried approach worked well for FD.
That first year, I ran short of time and just soldered leads to sheets
of copper and clamped those with hose clamps to the aluminum pipe. As
expected, corrosion developed rapidly. Then, I coated the copper with
one of the copper to aluminum contact compounds and corrosion never
developed even when I left them clamped together for many weeks. Still,
it would be better to clamp the copper over a SS shim to prevent copper
to aluminum contact, with appropriate compound in each interface. There
are other, better ways to make the connection, but I didn't pursue them
when this worked well for portable purposes.
I put one of these up at the home shack as an experiment, with 4 guys at
the 30' level. It buckled below the guys in a storm one night. I don't
recall the spacing from the guy anchors to the antenna. It was
moderately generous, but, obviously, not sufficient to prevent a slender
column failure.
The 0.050" wall irrigation pipe is not strong enough to withstand wind
without guys, even calculated with a very generous 30,000 psi yield
strength. Of course, once it yields, it buckles and folds over. 3"
irrigation pipe is available with thicker walls, but it is not high
strength, seamless tubing. I don't recommend it for anything other than
portable antennas at 30 feet or above.
73 de WOØW
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