Low Band Coil for Glass Fiber Mast Vertical Antenna

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This is a compact low band coil similar to those from Buddipole, designed to operate on 80 and 160 meters using a wire mounted on an 8 or 10 meter fiberglass mast (fishing pole). Different rings are available for various mast diameters. Initially, it was engineered for 0.8mm wire but I used standard 1.5mm² electric wire with the insulation removed. I employed 3.5x16mm wood screws to secure the posts and M5 screws with wingnuts to connect the radiator and the elevated 20 meter radial. The connection is made using a SO239 connector. As this antenna is asymmetrical, it's advisable to use a 1:1 balun or choke, or add a few windings to form a coil right after the antenna connection. I cannot recommend a specific radiator length since I simply attached a random wire that fit my 8 meter mast, tuned it and it worked. However, there is room for improvement by performing proper calculations and radiating pattern analysis using XNEC2 or MMANA, so feel free to experiment with this. Since this is a shortened antenna, its bandwidth will be significantly narrower than that of a standard half-wave antenna. For lower frequencies, I provided a stackable soil spool that can be mounted on top of the low band coil and connected using an M5 screw. The radiator will then be connected to the additional coil. This extra coil was not necessary for 80 meters, so it wasn't wound in this instance. I recommend using an antenna analyzer or VNA to determine the best clip position on the coil. As always, I have included the FreeCAD files for you to play with and experiment with.