But these harmonic currents will upset your readings somewhat - where on a
scope trace is the RMS value of
a) the total waveform   and
b) the fundamental  ?

The harmonic currents will obviously be out of phase with the harmonic
voltage, and cannot exit the top of the coil so if they are indeed entering
the coil base they must be completing their loop in the fields from the coil
itself - the quadrature, non dissipative,  H or  E fields.  Very little
radiation field will be generated from such a small radiating element, even
at harmonic frequencies.

There is nothing special about the coils we use on LF - (except the amount
of mystery they seem to generate)

Andy  G4JNT

The output voltage of the TX  was somewhat distorted due to harmonics,
showing up as some ripple at the positive and negative peaks of the
trace but  the zero crossings were at exactly the same points as the

voltage

over the resistor.
Thus as far as  can be judged from oscilloscope traces voltage and current
at the bottom end of the coil

Perhaps the statement in the article is not true, or not applicable for the
sort of coils we
use on LF?
Could that explain the succes of the helical antenna?