Copper Cactus Dual Band J-Pole Antenna Plans

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 schematic drawing of the dual band j-pole antenna plans
( Click Here ) Word doc
Dimensions j pole PDF
Print Instructions for this J-Pole

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

Materials

thumb_jpole2

dual band j-pole antenna plans

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″.

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 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

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)

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.

Building Suggestions

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
RG8x coax:

J-Pole Dimensions
J-Pole Dimensions
J-Pole.pdf
29.2 KiB
3016 Downloads
Details

J-pole Instructions
J-pole Instructions
j-pole_Instructions.pdf
167.7 KiB
1633 Downloads
Details

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.

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 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.

14 Responses to Copper Cactus Dual Band J-Pole Antenna Plans

  1. Allen says:

    First Name: Allen
    Country: US
    Web Site:
    Call Sign: n0sck

    Comments: I built the Copper Cactus Dual-Band Super J-Pole in 1992, twice. The first used the dowel, the second I used a PVC 1/2 inch female coupler and two threaded copper male adapters. I shortened the upper and lower elements by the amount the adapters added. I also drilled and tapped one of the flats of each adapter and used 1/4 inch compression to 1/8th inch male pipe adapters for the matching stub, again reducing the length by the appropriate amount. I also fashioned a mount for the SO-239 by splitting a 2 inch length of 1/2 inch copper lengthwise and flattening out 1 half while leaving the other half alone. During tuning I simply clamped this to the pole, after I found the perfect spot I soldered it in place. ( See Picture )

    This antenna has been up and in continuous use since 1992, It has never needed returned (I use a MFJ 269 analyzer to check periodically. The winds in Kansas do blow and this is the only antenna that I have that has not needed repaired!

  2. Matt says:

    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

  3. KD7GQC says:

    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 capacitive 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

  4. KC5DPJ says:

    KC5DPJ Modifications

    I made one of your “J-Pole” antenna’s with some mods. I cut 2 pieces of 1/2 tubing about 11/4″ long and split them. I cut a 1/4′ tab in the center of each, mounted my SO-239 to one and drilled a hole in the other for soldering the wire in. I used #10 solid copper wire for the center of the SO-239 to the short length of the “J”. I used two 7/8″ stainless steel hose clamps to hold each piece in place. I also used a full 3 foot length of 1/2″ dowel rod to join the two longest pieces together. I drilled three holes thru the copper and dowel on each long piece of copper and used 7/8″ 6-32 screws and nuts for each. This seems to add a great deal of support for the two.
    KC5RFL has an antenna analyzer and he checked my SWR’s. Came out 1.1:1 at 146.610mhz. Great.

  5. WB5HDS says:

    Call Sign WB5HDS
    State: NM
    Country: United States

    Comments: I’ve used 10ft sticks of 1/2″ galvanized ‘emt’ conduit to build my j-poles. i drill a 1/4″ hole where the “j” goes on and use a piece of 1/4″ copper and solder it in place, then attach the feed line. less than $6 invested using new parts. if you want a “super j”, then use a piece of 3/4″ pvc as an insulator and add your stub and pole, still very cheap. can’t tell ANY difference in performance. we hams have fun don’t we….Dave

  6. N3TZO says:

    Call Sign N3TZO
    State: MD
    Country: United States

    Comments: The antenna is up, and performing with nice results! All connections are soldered, and I decided to paint mine white (except for the match, which I shined and lacquered because it just looks cool). No more than 1.5:1 SWR at any point, and getting positive feedback on my signal. Thanks for the design info, and help.

    73′

    N3TZO

    http://home.comcast.net/~nutzo488

  7. KE4JOY says:

    I am considering building this dual band jpole

    Instead of the 3/8″ Cu tubing matching loop I am considering using some #8 bare solid Cu conductor I have around.

    I am wondering how that might affect any dimensions of the antenna itself or the matching loop and how it might effect the Q of the antenna.

    I like the jpole as I an simply affix a ring to the top part tie a rope to it and hoist it up a tree. I don’t have a tower or mast to mount it on.

    Thanks in advance!!!

    • Admin says:

      Yes, changing from tubing to wire will require a complete redesign of the antenna. [edit: Additionally, the bandwidth will be significantly narrower.]

      Especially on VHF and above, element diameter is a critical factor. [edit: On VHF even changing from 12AWG to say, 18AWG wire can throw a design out of wack.]

      The first rule of home brewing antennas from plans is to follow the plans exactly. especially with regard to dimensions of radiating and feed elements. Once you get it working then you can tinker with it.

      Failure to follow this rule will most often find you with a misbehaving antenna, and you will flounder in trying to make it work.

      Now, this rule is for those who want to build from plans. If you want to vary the design, then do the math and get the dimensions correct for you needs.

      Have fun! bill

  8. N2UHC says:

    I’ve been using a super J-pole for nearly 15 years now. You really can’t beat it for a good, excellently-performing 2m antenna. And the best part is they’re not hard to build.

    I used a wooden dowel rod between the upper element and the lower element (between the phasing harness) and even though it was coated with epoxy and well-painted, it eventually broke. I solved the problem by splitting a length of PVC pipe and fitting that over the upper & lower elements, with the phasing harness coming out of the split piece. That was held in place by four screws & nuts, though it fit so tight it probably wasn’t necessary. Since at my new QTH my antenna mounted near trees, I painted it with camouflage colors and it’s nearly impossible to see next to the tree.

  9. John Riopko says:

    Call Sign: kc4yha
    Comment: Built the Copper Cactus dual band today. Instead of 239 connector I clamped the insulator and core to the two locations. Once I get a final tune I am going to solder the wires to the antenna. SWR was less than 1.7 / 1 on both bands on initial test. I plan to mount the antenna in it’s final location and then do a final tune.

  10. Frank says:

    thank you worked out great, info was spot on.
    KK4CZT

  11. Etienne says:

    Is this a true dual band antenna, being 144/443 Mhz (VHF/UHF)

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