Originally Posted by Jim in Seattle Is there a formula to determine the length or perhaps the area or the 'best' shape of each bowtie-half, based on its' intended "center" frequency?
John D. Kraus, who is considered the "father" of the corner reflector, in his Antennas 2nd Ed. gives a design chart for the bowtie in a corner reflector on p 558 which says 4/5 of a wavelength for the total length of the bowtie. If you are interested in corner reflectors you really should borrow this book and read the chapter on reflector antennas. The general idea is that fatter elements don't need to be as long for the same resonant frequency.
In the VHf UHf Manual, 4th Ed., by RSGB there is a chart on p 8-15 for elements using tubing that tells how much shorter to make the collinear pair for different length to diameter ratios: Table 7. Resonant lengths of full-wave dipoles. For example: for a wavelength to diameter ratio of 50 the length would be 0.85 and give a feed impedance of 500 ohms.
Since you would be designing for only one channel the tubing would give the 1.6 dB extra gain over a folded dipole and be easier to calculate. If they are made too long you have less gain because the main lobe divides in two. You can see this in the gain vs frequency curve with 12" whisker bowties; the gain drops like a rock at the high end.
Your design calculations could be verfied with computer modeling. I'm not into computer modeling and have made a choice not to do it and let others do it for me. I'm 76 years old, have been doing antenna experiments since I was 8, and would rather spend the rest of my time building, and making empirical tests and measurements.
Your fondness of the folded dipole, corner reflectors, and directors makes me think that you would be happy with a 91XG UHF antenna; it has a lot of gain and is very popular.
WHY? Are they 'blockers from other directions?' How about if I cut them to a calculated length for a reflector for a 31 Yagi? Then they would be resonant. Is this a good or bad plan? - and why ---
The reflector rods of the corner reflector do indeed block signals from the rear and give an excellent F/B ratio, but their primary function is to reflect the incoming wave front to add it to the direct signal that is being picked up by the driven element which is located at the focal point of the reflector for increased gain. The reflector rods do not need to be resonant any more than the planar reflector wires of the 4221 or the dish of an antenna with a parabolic reflector need to be resonant.
Some hams have tried multiple resonant reflectors and found that they weren't worth the trouble. The case of trigonal reflectors giving 0.75dB gain comes to mind.
May I assume adding front directors would be based on the feedpoint of the bow rather than the forward bend of the bows?
Yeah I know, but then comes a new scope and a new...
So, how DO you tell if a new antenna is better, other than observing how your tuner acts at the "cliff"?
I had a private mailing (from a member here) regarding this particular issue and I intend to follow thru with his (bizarre) suggestion presented to me. I know this is a "black-art" and if his idea works I will share it here.
Good luck with the experiments, Jim!
I'm the last person who would tell you not to try something different. Kodachrome film, one of the finest color slide films, was invented by two "outsiders" Mannes and Godowsky who were musicians. The didn't know that it "couldn't be done," so they did it.