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!
First, collect the necessary parts… wire hoops and chassis mount UHF connector.
Then, straighten the croquet hoop wires.
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).
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).
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.
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:
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.
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.