Hi Red,
Were you able to find different pieces of pipe to make the bushings or did
you have to machine them?
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Red
> Sent: Friday, November 03, 2006 7:46 PM
> To: TowerTalk
> Subject: Re: [TowerTalk] Questions about Irrigation Pipe for Verticals
>
> 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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