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W4ZT
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Union
City, Georgia
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Copper
Plumbing Pipe Dipole Antenna
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During the late 1980's I worked up the design for these dipoles during a vacation week at home. I was looking for an antenna design for a repeater antenna. The design I wanted was something that was grounded to help prevent static buildup problems, was easy to build and could be duplicated over and over without redesign. These dipoles are the result of that effort and do a good job. One of these dipoles works fine for a basic, slightly off center, omni-directional antenna. The angle of radiation is lower than that of a ground plane so it does tend to work better (by about 3db in the favored direction). You can use more than one by stacking them vertically and feeding them in phase. Each time you double the number of dipoles you increase the gain in the favored direction by about 3 db but the amount of work that goes into the phasing harness and the losses might make it undesirable to stack more than 2 or 4. Stacking distance is just under 39 inches tip to tip so a pair of dipoles will be about 12 feet long. I built 8 dipoles and did put all 8 up in phase. They worked great but were VERY long and the phasing harness was a bear to build and install. If you want to go that far I might be able to give you hints but you're on your own after that. ;-) If you build one of these antennas I'd love to hear from you and see pictures of your work. 73, Tony - W4ZT |
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(Click
on the small pictures to view a larger picture in a new browser window.)
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Currently,
6 of the 8 copper pipe dipoles I built, are on the tower. These 4 near
the top (top of the dipoles is at about 95 feet) are fed in phase (using
a home made coax phasing harness). The feedline goes to the lab.
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The
other two are much lower (at about 35 feet), also fed in phase, and
are connected to the 2 meter radio in the dining room.
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This
is one of the old dipoles laying on the ground. You can see the nice
patina of the copper on the old dipoles.
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The
gamma match is a piece of 1/4 inch copper tubing which is soldered into
a hole drilled in the appropriate place along the 1/2 inch pipe.
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The
connection between the gamma match and the connector (I used BNC but
use what you like. See the other pictures showing the use of a UHF SO239
connector below. Note that the silicone sealant keeps moisture out of
the connections.
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| These drawings may help you understand the construction. They are not to scale and the gamma match is offset to provide better detail. These dimensions worked for me. You should make sure ONE dipole works properly for you before you build more. In mine, each side of the dipole was made using an 18 7/32 inch piece of pipe and the support arm was a 17 inch piece of pipe. That worked out for the fittings I had. You will need to double check yours before soldering. | |||||||||
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The chassis mount BNC connector is soldered into a "U" shaped piece of copper wire which is soldered into holes drilled into the copper pipe. The SO239 connector works well in this application as the photos below show. See the detailed photos and note the slot which the corner of the connector is soldered into. The gamma match is 1/4 inch copper tubing. At the end near the connector, a piece of RG59 coax center conductor is slipped inside a piece of brass tubing which telescopes into the 1/4 inch copper tube. It is then soldered to the connector. Sliding the brass tube in and out over the small exposed piece of the coax center tunes the gamma match. Note that the RG-59 center is just used as the gamma match. Feed the dipole with 50 ohm coax unless you are building a phasing harness for multiple dipoles (detail of the harness is not given here but it is a common "odd quarter wave" matching harness). |
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The
gamma section inside detail: New and Old.
The center is a piece of RG59 coax center conductor cut to 4 1/8". Strip 3/8" of the insulation away and make a right angle bend. NOTE: The insulation will come right to the bend. The insulation has come away from the end of the old wire during disassembly. The center conductor is telescoped inside of a 1 1/2" length of 3/16" brass tubing which will telescope inside the 1/4" inch tubing of the gamma. |
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The
SO239 connector makes a good choice for the dipole. I cut a slot in
the "T" connector as seen above with a die grinder and cutting
wheel. The slot is sized so that the corner of the connector will fit
snugly into it.
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The
SO239 fits just right in a slot cut with a cutting wheel on a die grinder.
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The
connector ready for soldering.
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You
can see the slot here with the connector in place.
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The
connector and gamma match are assembled and the antenna is ready for
adjustment.
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Another
view of the connector and gamma adjustment.
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Last update was on March 27, 2005 11:15
