I built it myself, based on the diagram. For the primary and secondary coils, I wound two turns each, with the secondary coil winding in a clockwise direction for 7 turns and then counter-clockwise for 7 turns. Finally, I set up and adjusted the antenna to approximately 20 meters, which allows operation at 10/15/20 meters. The maximum SWR is 1.6 and the minimum is 1.1. However, the 40-meter harmonic resonance reached 7.5 with a corresponding SWR of 2.8. I later consulted with several teachers, and it seems that factors such as the magnetic loop, antenna setup environment, height, magnetic loop model, matching capacitor, and magnetic loop winding density may be involved. I am currently investigating and making adjustments, so let's learn together!
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