SO-239 Antenna
By David White, WA7YFF-
Awhile back, I got to talking with someone in the club about this antenna. Unfortunately, I can't remember who it was, so I thought I would just make these instructions available to everyone. This is, after all, a very nice and easy antenna. I built a 2m version of this about a month after getting my Novice license, KB5QZP (but I had to wait until I upgraded to Technician Plus, KB5RRM before I could use it!). I followed the instructions exactly and I still use the antenna today. It has a beautiful 1:1.2 SWR up and down the voice portion of 2m and 440 bands. Enjoy!
One of the simplest antennas you can build is a quaterwave ground plane antenna. It is small in size and is inexpensive. The only part you will need to buy is an SO-239 panel mount connector. You can use an old wire hanger for the radiator and radials. You will need to use your soldering iron or gun to attach the Radiator to the center post of the SO=239. File any paint or coating from the radiator wire before soldering. Cut the radiator to the proper length before soldering it. If you can find a short copper tube to help secure the radiator to the SO-239, your antenna will stand up to high winds.
The radials may be soldered or attached with screws. Screws are the easier method if you take the time to overlap them as shown in the diagram. Cutting the radials may be done after the construction is complete.
The following charts are in decimal inches.
| FREQ | RADIATOR | RADIAL |
|---|---|---|
| 423.0 | 6.64 | 6.97 |
| 424.0 | 6.62 | 6.95 |
| 425.0 | 6.61 | 6.94 |
| 426.0 | 6.59 | 6.92 |
| 427.0 | 6.58 | 6.90 |
| 428.0 | 6.56 | 6.89 |
| 429.0 | 6.55 | 6.87 |
| 430.0 | 6.53 | 6.86 |
| 431.0 | 6.52 | 6.84 |
| 432.0 | 6.50 | 6.82 |
| 433.0 | 6.48 | 6.81 |
| 434.0 | 6.47 | 6.79 |
| 435.0 | 6.46 | 6.78 |
| 436.0 | 6.44 | 6.76 |
| 437.0 | 6.43 | 6.75 |
| 438.0 | 6.41 | 6.73 |
| 439.0 | 6.40 | 6.72 |
| 440.0 | 6.38 | 6.70 |
| 441.0 | 6.37 | 6.68 |
| 442.0 | 6.35 | 6.67 |
| 443.0 | 6.34 | 6.65 |
| 444.0 | 6.32 | 6.64 |
| 445.0 | 6.31 | 6.62 |
| 446.0 | 6.30 | 6.61 |
| 447.0 | 6.28 | 6.60 |
| 448.0 | 6.27 | 6.58 |
| 449.0 | 6.25 | 6.57 |
| 450.0 | 6.24 | 6.55 |
|
| FREQ | RADIATOR | RADIAL |
|---|---|---|
| 28.1 | 99.93 | 104.91 |
| 28.2 | 99.57 | 104.54 |
| 28.2 | 99.22 | 103.80 |
| 28.4 | 98.87 | 103.80 |
| 28.5 | 98.53 | 103.44 |
| 28.6 | 98.18 | 103.08 |
| 28.7 | 97.84 | 102.72 |
| 28.8 | 97.50 | 102.36 |
| 28.9 | 97.16 | 102.01 |
| 29.0 | 96.83 | 101.66 |
| 29.1 | 96.49 | 101.31 |
| 29.2 | 96.16 | 100.96 |
| 29.3 | 95.84 | 100.61 |
| 29.4 | 95.51 | 100.27 |
| 29.5 | 95.19 | 99.93 |
| 29.6 | 94.86 | 99.59 |
| 29.7 | 94.55 | 99.26 |
| 29.8 | 94.23 | 98.93 |
| 29.9 | 93.91 | 98.60 |