This is a 125-foot tower, fed at 90 feet, by a cable 2 feet from a face
of the tower. This makes a loop about 184 feet in perimeter. This
perimeter is less than 0.1 wavelength. Thus, we have almost equal
currents flowing in opposite directions at any two points in the loop
and they are diametrically opposite each other. If there were no
separation between the cable and the tower, there would be no radiation
resistance, As it is there is very little radiation resistance.

Radiation resistance can be increased by lengthening the loop or
widening the loop. As long as the loop`s perimeter is less than
1/2-wavelength, it will have an inductive reactance which may be tuned
out by the vacuum variable capacitor. Were the tower a 1/4-wavelength,
it would be self-resonant and require no tuning. It is much shorter than
that.

To boost radiation, I would suggest extending the feed-cable to the top
of the tower to get current up there and to raise the feed-loop
radiation resistance. 1/4-wave folded unipoles radiate almost the same
as open-circuit unipoles. Shorter antennas will suffer by comparison.

I`ve installed aircraft beacons at my company`s airstrips around the
world but they were series-fed and used the 3-strand top loading
referred to in this thread. They all worked fine on original fire-up.

Best regards, Richard Harrison, KB5WZI