2 meter 70 Cm Copper Cactus J-Pole Antenna
Home Brew Dual Band J-Pole Antenna Plans
How to Build a Dual-Band Antenna for 2M/70cm? Your going to like this 2/70 Dual Band J-pole Antenna Plans known as the Copper Cactus Dual Band J-Pole, This home-brew j-pole antenna 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 had 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 nice calculator as well showing the proper lengths for a given frequency. I strongly recommend using this to do the design: Super J-Pole Calculator
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.
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″.
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 fiberglass rod
1 – SO-239 panel mount coaxial fitting
1 – Piece of # 14 stranded copper wire
2 – 3/8″ by 7/8″ stainless band clamps
- Tape measure
- Tubing cutter
- Propane torch
- Solder and flux
- Electrical tape
- Caulking compound
- 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)
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.
You may use a fiberglass 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.
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.
Be sure to keep the flame of the torch away from the insulator to avoid burning it.
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.
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.
Use a ruler or caliper to check the spacing between the 19″ and 57-1/2″ pieces, to keep them parallel to each other.
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.
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.
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.
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.
A 1/2″ pipe coupling and a length of pipe may be used in place of floor flange for mounting in a roof tripod
Attaching coax to the radio
Here are a couple of youtube videos that
show you how to attach a pl-259 connector to both the thicker RG213 and thinner
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.
- 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 attach 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)
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 copper cactus J-pole, Guess that’s good in a way, but would love to either way Praise or Suggestions about this project.