[TowerTalk] Questions about Irrigation Pipe for Verticals

[Red]

Hi, Gary;

I machined them from a piece of 3" OD 1/2" wall aluminum I found at a 
scrap yard.  Just got lucky!  I have a small lathe and removed a few 
thousandths from the ID for bushings at the top of the 3" pipe and a few 
from the OD for bushings at the bottom of the 2" pipe.

An alternative is to turn the bushings of wood with four to six pieces 
of thin aluminum, fastened to the appropriate pipe and extending over 
the wood between the pipes.  Make this assembly rather loose so it will 
slide easily.  One of us should calculate the reactance across the space 
between a foot or more of the two pipes; maybe the electrical contact 
isn't very important at HF.

73 de Red

Gary Schafer wrote:

>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 at contesting.com [mailto:towertalk-
>>bounces at 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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