I had some junq lying around and I wanted to build a 2m ground plane antenna for one of our local technicians. I scoured the internet and found a lot of plans but I wasn't satisfied with any of them. Many plans using an SO-239 didn't include any means of fastening to a tower or mast. Others had poor bolt-on designs for the radials by looping the radial around a single bolt to fasten them to the SO-239. It seemed to me that this method would work loose over time. So, I scratched my lumpy head and set out to make a better design.
First, I cut a piece of 1.5" x 1.5" aluminium angle to 1' length and rounded the corners using a quarter as a template for aesthetics and safety.
Second, I marked and drilled holes for a mounting u-bolt that I had in my junq box.
Third, I marked and drilled holes for the SO-239 socket.
Fourth, I cut four radials at 20 5/16" from some stainless steel scrap whips I had been saving. Any number of materials can be used for this such as: welding rod, coat hangers, ground wire or stripped romex. Then I sandwiched the radials between the SO-239 and the aluminum angle as pictured below.
Finally, I cut a vertical radiator at 20" from some scrap heavy gauge ground wire. I filed the end of the ground wire until it fit into the SO-239 center conductor and soldered it in place. (Not shown) Then, I sealed the soldered connection using grey RTV sealant--silicone will also work for weather proofing.
To finish the project, I will use an antenna analyzer to tune the antenna by trimming the radiator and radials 1/8" at a time until my desired resonant frequency of 146.520 is acheived.
This is a cheap, effective and easy homebrew project for 2m. It can be modified for any frequency. I believe this design will prove to be more durable and easier to mount than others that I have seen.
73 de KE5ZRT