I re-measured and cut new wire and added a ground grid (a four-foot square of chicken wire) and it still doesn't work. The way that it appears to not work is interesting, so I'm recording it. The feedpoint impedance is very small. I was expecting about 100 ohms, and it's less than 20 ohms from 24.682 MHz to around 30.508 MHz and at most of the frequencies in the range, it's less than 10 ohms. I also discovered that I needed to disconnect the resonator from the ground plane to get those numbers. The simulations all connected the resonator to the ground plane.
The results of the actual test:
| Frequency (MHz) | Rs (Ohms) | Xs (*i Ohms) | SWR (R0 = 9 ohms) |
|---|---|---|---|
| 24.682000 | 2.000000 | 51.000000 | 149.215521 |
| 24.992000 | 2.000000 | 48.000000 | 132.714687 |
| 25.504000 | 3.000000 | 42.000000 | 68.652100 |
| 25.996000 | 4.000000 | 36.000000 | 38.668584 |
| 26.505000 | 5.000000 | 30.000000 | 22.310734 |
| 27.007000 | 6.000000 | 24.000000 | 12.754932 |
| 27.506000 | 6.000000 | 17.000000 | 7.383074 |
| 27.994000 | 8.000000 | 10.000000 | 3.077879 |
| 28.507000 | 9.000000 | 3.000000 | 1.393487 |
| 29.000000 | 9.000000 | 13.000000 | 3.824981 |
| 29.501000 | 11.000000 | 24.000000 | 7.729206 |
| 30.009000 | 13.000000 | 39.000000 | 15.070397 |
| 30.508000 | 16.000000 | 56.000000 | 24.076521 |
I don't know what I'll try next. I think I'll consider my options.