…homebrew antenna…

So, What do you do if you have a UHF SO-239 chassis mount coax connector and a bunch of croquet wire hoops sitting around… and you’re bored?

You build a 1/4 wavelength groundplane antenna!

groundplane antenna

First, collect the necessary parts… wire hoops and chassis mount UHF connector.

groundplane antenna

Then, straighten the croquet hoop wires.

groundplane antenna

Next, you’ll want to measure the wires for your frequency. Mine came out at about 19.25-19.26, since my target frequency is 145.800 (ISS).

groundplane antenna

What’s next? Cut the wires. (Note: some sites recommend leaving the radials up to 20% longer than the vertical element. I don’t know a lot about antenna theory, yet, so I split the difference and cut my radials to 19.75).

groundplane antenna

Remove the coating near the end that will mount to the coax connector for the vertical element, and clean up the metal wire with some sandpaper.

groundplane antenna

By pure luck, this is how well the wire fits into the end of the UHF coax connector. Beautiful! Add a touch of solder, and the vertical element is done. Be careful while soldering. The vertical element will carry a lot of heat away from the soldering iron, and I melted the plastic a wee bit. Of course, I’m using a crappy uncared for soldering iron…

Now the hard part… how to fit the radials to the chassis mount? If I had a die that small, I could have cut threads on the end of the radial wire, bent the end into an “L” shape, and mounted it to the coax chassis with a nut on each side of the hole. But, it was not to be that easy for me…

Solder? I was not having much luck doing any kind of soldering on this chassis mount connector. So that was out. After stewing on it for a couple hours and rummaging the garage, I came up with this:

groundplane antenna

Crimp-on wire connectors. These did not easily go on. I had to open up the crimp tube a bit with a nail to get them to slip over the croquet wires. Since there is no “give” in the croquet wires, the crimps don’t exactly work like crimps. So, this is a temporary solution since the wires will slowly work their way out of the crimps with a little jostling here and there over time. But, it allowed me to continue with the build!


Then, you put a little bend in the radials, and attach them to the UHF chassis connector.

groundplane antenna

Then, you cut a hole in the side of your PVC antenna mast base, run your RG-6 antenna cable, and test your radio!

So far, I have great tx/rx with the repeaters I can normally hit with my j-pole. However, I had no luck with the ISS, though it wasn’t a close pass… So, I’ll watch the passes, and try again on a closer one.

End result? I have a VERY inexpensive 1/4 wavelength groundplane antenna for very little effort! Great project.

14 comments so far

  1. Hans PD0AC on

    Nice project! In the past, I used old whip antennas which came from old disassembled portable radios. You could easily change the working frequency by changing the length of the individual elements.

    A ground plane has some interesting ‘angle of attack’ characteristics, especially on bands such as 10 meters. On more than one occasion, I could hear and work stations that were hardly noticeable on horizontal antennas.

  2. Richard 9W2CBL on

    Hey! nice project there!

  3. bloodhound on

    Thanks! Thank you both. I’ve been messing with the antenna, and it’s holding up better than expected. Definitely a fun garage project.


  4. Tim G4VXE on

    Nice project, Jason. Julie & I wondered if croquet is particularly popular in Hawaii, or maybe that’s why you made the antenna out of the hoops πŸ™‚

  5. bloodhound on

    …yeah… we weren’t doing much with the croquet hoops. In fact, I’d already scavenged other “croquet parts” for other projects.

    You can see that I used the bag to hold my portable antenna project for my FT-7800R.

    You can see that I used a couple of the mallet handles as a makeshift bike stand on my other blog, http://back2dabike.wordpress.com. Look for the post on the Giant OCR 3 build.

    Now, what to do with the rest of the mallets and the croquet balls… πŸ™‚

  6. KF6HCD on

    Very nice.

    When I used an SO-239, I gound down around the mount hols and soldered in the radials(wire coat hangers-leave the varnish except for the solder area- file/sand that off) with bit of crimp and a LOT of heat. Then, bend ’em down to the proper angle. I did that before I mounted the vert. Then, just a bit of heat, and the vert is in place. A bit of shrink tubing, and then everything is in place and solidly insulated.
    Your mileage may vary, of course. Smiley…

  7. Todd WH6DWF on

    This looks like a fun project, I was wondering if you bought those wires at City Mill or if you remember where you bought them?
    Did you get a QSO with the ISS with this antenna yet? I am sure that you could hit the Diamond Head repeater at 146.880 Mhz on 2 meters, how well did it do with other bands?
    Mahalo and 73!

  8. Bill on

    A very good first antenna project.
    I would have cut off the blue plastic, crimped and soldered the connectors.
    I use brazing rods to make these ground planes and bend the rods with heat to make loops and use stainless steel 440 nuts + bolts to connect them to the through chassis connector ears. No rust that way.

    • Todd WH6DWF on

      Aloha Bill,
      I totally agree with you on that one. I built two of these last year and they work fantastic! I used steel metal hangers that I bought at Wal-Mart and crimped looped wire connectors and used stainless steel nuts and bolts. Unfortunately, the metal radials I made have started to rust and may have to make news one’s soon unless I can find the same size wire in stainless steel.
      What was real helpful was ARRL’s Antenna Calculator for the UHF frequency that I was going for. I cut my radials at 6.75″ and the vertical at 6.25″ for 1/4 Wave and used two fishing sand spikes to mount them on the rails of my lanai and connected them both with a “T”connector to get some very awesome gain. Together, I get slightly better than a 1:1 ratio on my SWR meter.
      Besides making new radials out of stainless steel, I think I would on liked to use 50 Ohm cable for one side of the “T” and 75 Ohm cable of the other side to make them a lot more capable with each other. I use two instead of one because the 70cm signal has to weave between these buildings here in Waikiki before reaching me on the other side of Waikiki from the repeater on top of the Frank Fasi Building in downtown Honolulu.
      I learned from this project that it is helpful to have a few of these SO-239 connectors ready in your emergency radio go kits if you have to make some antennas in the field on the fly. You divide the frequency that you are going for into 234 for 1/4 Wave and 219 for 1/2 Wave and your answers with come out into feet and then translate that into inches and cut. You can cut your vertical 1/2 inch to 1 full inch and you’re in business.
      This a very simple project that gains fantastic results within 20-30 minutes time during an emergency event or in a pinch. Great first time project to find the antenna builder in all of us. Mahalo and 73!

      • Todd WH6DWF on

        I got the length of the radials and vertical backwards,it should be 6.25″ for the radials and 6.75″ for the vertical. A simple mistake but caught it quickly. Have fun building this very effect antenna. Mahalo!

  9. Bill Hayward on

    I recently made a 2m and a 70 cm ground plane out of Fan Guards. The grill that stops your child from putting their hand near the blades after you told them not to.
    I saw the project somewhere I can’t remember and it was called FanTenna.
    I will bring the 70 cm FanTenna to the mini field day to show it off on a camera tripod.

    Anybody have an SWR meter for 70 cm? The 2 meter Fantenna is nearly 1.1:1.

  10. Donn on

    I’m a fan of copper coated steel welding rod. 3/32″ I believe. They can be had for about 25 cents each. The copper coating facilitates soldering. I bend a little loop in the outside ends to help protect someone from losing an eye. A lady, one of my ham class students, scared the dickens out of me the way she was waving those things around. πŸ™‚

  11. Keith on

    I like it. Looking to make a 2 meter ground plane, was using google, and this blog was on page 3!

    I want to mount something at the house and this style antenna may be the one i use.

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