Reg , What is your opinion about the effectiveness of (a) counter
poise(s)
of any length in series with an adjustable series resonance circuit
,adjusted for maximum RF current at the operating frequency ?

Frank GM0CSZ / KN6WH
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Frank, the effectiveness of a counterpoise depends on its input
resistance. The lower this resistance better it is. It is the
'ground' connection for the antenna. (And the transmitter).

But there's no point in making it longer than 1/4-wave. This increases
coupling with the ground, increases loss resistance and also
undesirably increases radiation resistance. The counterpoise then
behaves more like a very low antenna.

When it is 1/2-wavelength long it has a very high input resistance and
is entirely non-effective. It may just as well not be there.

At some lengths the loading coil would have to be replaced with a
loading capacitor.

Remember, the antenna wire plus counterpoise is behaving as an
off-centre fed, bent, dipole with the lower section being very near to
the lossy ground. (Whatever the ground is). We don't want the lower
section to be TOO long. The current into the counterpoise is the same
current as is entering the antenna. If there is an antenna tuning unit
it will tune up the counterpoise simultaneously with the antenna. They
behave together as one thing!

So there is no point in having a separate tuner just for the
counterpoise. Maximum current flows into the counterpoise at the same
time as it flows into the antenna proper.

The purpose of the loading coil in the counterpoise is to provide a
low impedance connection to the braid of the coaxial feedline. If
there is no feedline then it provides an artificial 'ground' for the
transmitter plus tuner.

And all the foregoing arises because it is difficult or impossible for
the station owner to provide a set of buried ground radials.
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Reg, G4FGQ