Richard Cl;ark wrote:
"The radiation resistance of an antenna is NOT necessarily the same as
the drivepoint impedance of the antenna."

True, but for many resonant antennas they are identical.

Fundamentally, the radiation resistance is the value when inserted in
series with an antenna will consume the same power as that radiated.
Unless otherwise specified, the radiation resistance is referred to a
current maximum point in an ungrounded antenna, and to the base of a
grounded antenna. See 1955 Terman page 890 and 1950 Kraus page 143. They
agree.

All of ON4UN`s loaded antennas have maximum current at their drivepoints
and they are resonant, so their feedpoint resistance coincides with
their radiation resistance in all the instances diagrammed in the
current distribution chart for short loaded verticals. ON4UN starts with
1A current to the base of all antennas and the current declines from
that value. Its value is the cosine of the number of degrees from the
feedpoint in most cases.

Best regards, Richard Harrison, KB5WZI