I had the chance to attend a pretty neat presentation at a ham club in Mesa earlier today on building “flying saucer antennas” for the HF bands. (I took both my Technician and General tests at this club in 2019, and they are a terrific bunch of mostly retired folks with the amateur radio bug.)
These antennas are pretty cool little things because they seem to work pretty well, yet are very compressed in space requirements.
They are sort of like the capacitive hats you can get for the upper part of your vertical antennas, and are another type of loading coil, but being placed at the top of an antenna instead of in the middle like most coils, don’t reduce the circulating current above the coil.
One other problem this particular design solves is the issue of interturn capacitance, which in a completely flat planar coil setup can be quite severe. This design avoids that excessive capacitance by “basket-weaving” the coils over and under a series of spokes. (They remind me of the “star” Christmas ornaments we used to make with colored string woven onto popsicle sticks when I was a kid.)
The presentation included some live examples the presenter had built for different HF bands. The longer wave-length bands were, of course, larger in total diameter, and had more windings on the spokes, but compared to a huge half-wave dipole were quite compact.
The presenter uses a vertical shaft of just 14″, and a mag-mount with the flying saucer “hat” on his car to work HF bands from 6m to 160m (Depending on the hat used.)
Now I was thinking they would also be a terrific apartment antenna. (I like my hamsticks, but 30m is the longest wavelength I’ve worked so far. I use a Wolf-River Coil mounted at the window for 40m.)
Here are a couple of links to articles I found online about this type of antenna “resonator”.
- http://play.fallows.ca/wp/radio/ham-radio/flying-saucer-resonator-build/ This fellow 3D-printed his hub pieces instead of cutting them out of some stiffer plastic. Sounds like my kind’a thing!
- http://marac.org/roadrunner/1006rr.pdf (Start reading on page 12 of the PDF)