Richard Clark wrote:
"So how do the "ohms" of free space differ from the "ohms" of a quarter
wave monopole`s radiation resistance?"

Terman says something like: the radiation resistance has a value that
accepts the same power as the antenna takes when the equivalent resistor
is placed in series with the antenna."

Roy Lewallen has already said that the resistance of free-space is the
ratio of the E-field to the H-field. Fields relate to the forces they
exert. No amps in empty space which has no electrons. Only when a
conductor is inserted is there a path for electrons to travel in.

Evidence that antenna impedance does not define radiation is the
identical radiation produced by antennas which are very different.

The folded monopole and the quarter-wave vertical are quite different.
The monopole is a small squashed loop. The quarter-wave vertical is a
single rod. Feed point resistance is 150 ohms for a typical folded
unipole and it is 28 ohms for the typical quarter-wave vertical. A look
at Arnold Bailey`s catalog shows identical radiation patterns and gain
for both antennas.

Best regards, Richard Harrison, KB5WZI