Inspired by N1LO shortened mobile vertical: http://www.qsl.net/n1lo/mobilhf.pdf
Learned that very critical for efficiency is loading coil - must be airgap construction in order to reduce stray capacitacne and dielectrical losses. The coil shold not be “narrow and high”in order to maintain high Q.
1. Designing and printing the coil support on 3D printer, material is PET. Consists of top, bottom part and 4x comb sticks. All plastic parts are assembled together and form one piece.
2. Preparing Cu wire, diameter is 1.7mm, wound on plastic pipe of 10cm diameter and taken down from the pipe.
3. Cu spirale is easily wound on coil support. Wire pressed/clicked into openings on perimeter and fixed at both ends. All goes smoothly, I’m missing only a few last windings so now the antenna resonates at 4.3 MHz. After adding missing windings it should be OK also for 80m.
Next version of support will need to be stronger as middle of the coil is now slightly shrinked by pressure caused by windings.
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