A simple, low-cost, trapless short vertical antenna which amazingly works on three HF bands (20, 15 and 10 meters).
The only critical adjustment is the length of the coil, which mainly affects performance on the 20 meter band. 5 meters is a bit too long for the spiral coil wire, so you should find that the antenna is initially resonant somewhat below 14.2 MHz. Carefully lower the antenna repeatedly, shortening the spiral coil to bring the antenna into resonance near 14.2 MHz. I ended up with a 4.75m coil length. If you were able to duplicate my design parameters, you should find the performance on the 15m and 10m band to be as shown in the SWR charts.
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