Copper Catus
TREASURE VALLEY RADIO ASSOCIATION

Copper Cactus Dual-Band Super J-Pole Antenna Project

2 meter 70 Cm Home brew antenna

Your going to like this Copper Cactus J-pole , This home brew j-pole is easy to build and sturdy, While looking for an antenna project to build I remembered seeing a Marine antenna called the Super J-Pole in the  which had6 db gain over a quarter wave ground plane. I have had very good results working with copper J-Poles, so I built my refined version of the classic J-Pole. I then added a short insulated section, the extra half wave of vertical length, and the needed half-wave matching stub.

Here is a schematic drawing of the J-pole ( Click Here ) Word doc
Here is a schematic drawing of the J-pole ( Click Here ) PDF

Materials

Bottom of Catus

All the materials except the S0239 fitting can be found at any good hardware store, and the whole antenna can be made in less than an hour.

In my design I use 1/2" copper schedule M tubing and 1/4" soft copper tubing. I had experimented with using Teflon insulator, but have since changed my design to use a 9" length of hardwood dowel with three coats of lacquer as the insulator, for more strength.

Clean all the tubing, and then from the 1/2" tubing cut one piece each of the following lengths: 57-1/2"; 38"; 19"; 2", and a piece about 3" long for a stub to mount the antenna. In addition to the tubing, buy a 1/2" elbow, a 1/2" Tee, two 1/2" end caps a 1/2" threaded fitting, and a cast iron floor flange for mounting. Get a piece of 3/16" or 1/4" soft copper tubing 42" long. Find the center of the 1/4" tubing and bend it around a 1"-to-1-1/4" diameter water pipe or dowel.

Put the Heat to it

Now fire up the torch and start the assembly process from the bottom. See Figure 1. Use flux on all joints, solder the 1/2" threaded fitting to the mounting stub, and solder the 1/2" Tee fitting. Then proceed with the 57-1/2" section, 2" cross piece, and 19" section. Pay close attention to getting the 19" piece parallel to the 57-1/2" piece. After these have cooled, drill through both the 57-1/2" section of the 1/2" tubing and the hardwood dowel about 1/4" from the top end of the 1/2" tubing, and the bottom of the 38" section of the tubing. (See Photo A.) Then insert the 1/4" tubing to the 1/2" tubing and sweat solder the end caps. After these have cooled, clean the entire antenna, bend the half wave matching section to a half circle of about 4" radius around the antenna to help the balance and match.

Middle Section

Simplify the Feed Point of the J-pole

The feed point also needed to be made simpler, so I elongated one of the mounting holes of a panel mount SO-239 fitting and inserted a stainless steel adjustable band clamp. This goes on the 57 1/2" long section of 1/2" tubing. A short 2-3/4" length of # 14 copper stranded wire is soldered to the center terminal to go over to the 19" section. I used another stainless clamp to attach this. (See Photo B.) While experimenting to find the proper feed point, I found that the distance above the crossbar should be about 3".

Part's List

  • 1 -  10-foot section of schedule M 1/2" copper tubing

  • 1  - 1/2" copper elbow

  • 1  - 1/2" copper Tee fitting

  • 2  - 1/2" copper end caps

  • 1  - 1/2" copper threaded fitting (for mounting)

  • 1 -  1/2" cast floor flange (for mounting)

  • 1 -  Piece of 3/16" or 1/4" soft copper tubing 42" long

  • 1  - Piece of 1/2" hardwood dowel of Fiberglas rod

  • 1  - SO-239 panel mount coaxial fitting

  • 1  - Piece of # 14 stranded copper wire

  • 2  - 3/8" by 7/8" stainless band clamps

Tools needed

  • Tape measure

  • Tubing cutter

  • Propane torch

  • Solder and flux

  • Electrical tape

  • Caulking compound

  • Screwdriver

  • A weight to keep parts aligned while soldering

  • Steel wool or a Scotch Brite pad (for cleaning all copper)

  • Spray can of clear exterior lacquer (to finish-coat completed antenna)

Building Suggestions

1. You may use a Fiberglas rod as an insulator, but you will have to be very careful with the torch or you may weaken or burn the rod, or make it brittle.

2. When cutting the 1/2" copper tubing, cut the 57-1/2" piece from one end of the 10" length, and the 38" piece from the other end. By doing this you will have factory-cut edges for inserting the 1/2" dowel.

3. Be sure to keep the flame of the torch away from the insulator to avoid burning it.

4. Use paste flux on all joints when fitting the pieces together. Use enough flux, since you will be cleaning the entire antenna with solvent after assembly.

5. Use a weight to hold the 19", 57-1/2", and 2" pieces, and the Tee and the elbow, flat when they are sweat soldered together.

6. Use a ruler or caliper to check the spacing between the 19" and 57-1/2" pieces, to keep them parallel to each other.

7. When drilling the SO-239 fitting, use the drill press. Be careful not to drill into the threads of the fitting. After the holes are drilled, file the opening flat for a better band clamp fit.

8. After the best match has been found, you may want to solder the SO-239 and the stranded wire end to the 1/2" tubing.

9. When the antenna has been cleaned and matched, spray the entire antenna with a coat or two of clear lacquer to keep it looking nice.

10. After everything else has been done, apply silicon or a butyl rubber compound to the insulating section, then cover the joint with electrician's tape for a weather tight seal.

11. A 1/2" pipe coupling and a length of pipe may be used in place of floor flange for mounting in a roof tripod

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j-pole12.jpg (23828 bytes)
Suggestion by KB9TIO

 An Improved(?) feed arrangement is to use copper couplings, same size as the tubing. Split the coupling lengthwise, bend out @ 1/4" and notch for the so-239 inner ring. attach with sheet metal screws an/or solder so-239 to coupling. repeat with 2nd coupling and solder other end of #14 wire to flat on coupling. this provides a strong joint and very easy tuning by sliding the couplings up or down the tubing as needed. this tip was given to me by Tom-KB9OZZ

Thanks, Matt KB9TIO

Suggestion by KD7GQC

I have also seen variations on the J Pole which omit the insulator section. In the first, the center conductor is soldered directly to the driver element, and the entire antenna is thus at DC ground. The second variation is also an all-copper design, but you capacitively couple the RF to the element, by wrapping several turns of insulated wire from the center conductor around the driver section of the J pole. I can't vouch for the second approach, but the first seems to work great, for installations where a DC short to earth; is not a problem. It seems to me that eliminating the insulator section makes for a simpler, and potentially stronger, design. Kudos on a great antenna! 73s, Brian KD7GQC
One last suggestion:   put a piece of steel about 1/2 or 3/8 of about a foot and a half up the center of it ( from the base ) this will strength the bottom portion of the pole.. put a small curve in it so it touches the inner wall of the pipe.. my parents use this j-pole and live in a windy area.. and this fixed that problem.
In order for these instructions to work great.. Please send me feedback on if you had problems and what can be done to help the next ham.. I don't get much feedback on the J-pole, Guess that's good in a way, but would love to either here Praise or Suggestions about this project.

FAQ's

Is there a specified distance between the top and bottom sections (where the 1/4" soft copper attaches.  ( Answer is No ) About a 1/2 inch
How do you attach the soft copper to the two sections? Drill 1/4 inch holes through pipe and wood and insert 1/4 soft copper through and solder ends.
I was wondering how you mounted the S0239 onto the 53" pole. I was thinking of drilling a hole and get the wire out from the other side to hold it better but then when I read your description closely I saw that you mention that you used the band clamp. ( Answer ---Hard to describe but take your drill and drill a few holes between 2 of the 4 holes on the so232 then try to remove the rest of the material between these two holes, enough to get the band clamp through then attatch to 53 inch pipe and take the 3 inch or so 14 gage wire, solder to center of the so232 and attach to other side with 2nd band clamp)

Suggestion: k6dbg

I just built a copper cactus, tuned for 144.39, based in part on your plans. I found I was able to get a much better match by making a small balun near the feed point - four loose turns of the coax. You might want to try this and mention it if you like it.
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