Optimal random-wire lengths (in metres)
I have been experimenting with random wire antennas, and it seems as though it's not completely random. Some
lengths appear to work better than others.
This page contains a table, but it's in
feet, and so I've recalculated it in metres.
| Frequency (MHz) | 1/2 Wave | 2nd multiple | 3rd multiple | 4th multiple |
| 1.9 | 77.4 | 154.7 | 232.1 | 309.5 |
| 3.8 | 38.7 | 77.4 | 116.0 | 154.7 |
| 7.2 | 20.4 | 40.8 | 61.3 | 81.7 |
| 10.1 | 14.6 | 29.1 | 43.7 | 58.2 |
| 14.2 | 10.4 | 20.7 | 31.0 | 41.4 |
| 18.1 | 8.1 | 16.2 | 24.4 | 32.4 |
| 21.3 | 6.9 | 13.8 | 20.7 | 27.6 |
| 24.9 | 5.9 | 11.8 | 17.7 | 23.6 |
| 28.5 | 5.2 | 10.3 | 15.4 | 20.6 |
| 51.0 | 2.9 | 5.8 | 8.6 | 11.5 |
The 1/2 wave was calculated as 150/freq, the 2nd multiple as 300/freq, the 3rd 450/freq, and the 4th as 600/freq, with a velocity factor of 0.98
This means that the following lengths to avoid for a random wire:
2.9, 5.1, 5.8, 5.9, 6.9, 8.1, 8.6, 10.3, 10.4, 11.5, 11.8, 13.8, 14.6, 15.5, 16.2, 17.7, 20.4, 20.6, 20.7,
23.6, 24.4, 27.6, 29.1, 31.1, 32.5, 38.7, 40.8, 41.4, 43.7, 58.2, 61.25, 77.4, 81.7, 116.0, 154.7 232.1, 309.5
This means the following lengths are good choices, as they're far away from problematic lengths:
4.0, 7.5, 9.5, 12.8, 14.6, 17.0, 19.0, 22.2, 26.0, 30.1, 31.8, 35.6, 50.9, 69.3, 98.9, 135.4, 193.4, 270.8
Please note - you may need to adjust the lengths slightly.