"So in case it's back to inverted Ls (either extended or regular) it
would also be nice to have views on the original question. What
theoretically and practically appears to give the best results, the
extended L or the quarter wavelength L."
The comparison is dwarfed by the ground issues. If the ground/counterpoise is
lossy the higher feed impedance of the extended L will force less current
through the loss and make it more efficicient. If the ground system is 50 or
60 radials, the extended L will have some mild pattern shift to high angle
that may or may not be useful to an given operator.
OUT IN THE OPEN, an extended L long enough to make a simple series capacitor
match to 50 ohms, and over 50 or 60 radials, is a high performing classic
simple omni-directional antenna for both short and long haul.
However, since so many seem to use a tower as a support for an L, performance
predictions get defeated by the unpredictable aspects of a tower, the actual
electrical height of the tower in wavelength, miscellaneous conductors running
off it for miscellaneous lengths on top of the ground or buried, top-loading
by other antennas, tower grounding, radials, or lack of either or both, etc.,
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