Biconical Antenna Build

Antenna properties

Biconical dipole antennas (wikipedia link) are just two cones with the pointy ends at each other. They are supposed to have fairly good impedance bandwidth and good *pattern* bandwidth over that same wide range. In retrospect I think I should've just cut the frustrum shape out of aluminum flashing sheet for all the tedious soldering work assembling this out of copper coated steel welding rods took. All hooked together the conductive structure stands about 2m tall. Some day I might add curved end caps to the cones but it'd complicate the support structure.

The frequency range should be like a very fat dipole on the low end and limited by construction errors on the high end. I did make the top of the cones out of tin sheet so they're pretty smooth. The join is also a very small gap distance. So the 15 db return loss defined low end might be ~300 MHz and the high end somewhere in the 2-3 GHz range. I'll measure with a VNA sometime.

Support structure

I thought about how I wanted to do the mechanical support in depth and made plans for how to do it for weeks. Then when it came time to build I ignored the square box plans and did something entirely different. So I could only use 3 rods I decided to make a tensegrity prism. As a single person the challenge of holding it all together and upright while running the cord (and fishing line) was daunting. I let it fall off center sloppily while I went in a circle around the triangle progressively tightening all the tension lines between the compression spars. The zip ties holding the spars to the copper ring at the end of each cone helped a lot.

Anyway, here's a progressive series of photos from tin frustrums rolled into cones to a working antenna standing outside.



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