Recently I bought a used copy of "Reference Data for Radio Engineers"
published by Howard Sams in 1975. On page 27-6 the following applies to
this topic:

QUOTE

The effective height of a grounded vertical antenna is equivalent to the
height of a vertical wire producing the same field along the horizontal as
the actual antenna, provided the vertical wire carries a current that is
constant along its entire length and of the same value as at the base of the
actual antenna. Effective height depends upon the geometry of the antenna
and varies slowly with wavelength. For types of antennas normally used at
low and medium frequencies, it is roughly 1/2 to 2/3 the actual height of
the antenna.

For certain antenna configurations, effective height can be calculated by
the following equations.

Straight Vertical Antenna: h = 1/4 lambda

Effective Height = [lambda/pi*sin(2*pi*h/lambda)]*sin^2(pi*h/lambda)
where h = actual height

clip

END QUOTE

This may be useful toward the earlier thread started here by Reg ("Back to
fundamentals"), that went off in several directions.

RF