Previously, about BL&E's 1937 measurements:

Their calculation of the field at the receiving site when the radial
system is perfect was adjusted for the effect of ground wave attenuation
caused by the imperfect ground conductivity.

Anybody: Just wondering -- how does this conclusion flow from the findings
published in the 1937 I.R.E.paper of BL&E?

The theoretical (not measured) BL&E groundwave field at 1 mile for 1 kW
radiated from a perfect monopole over a perfect ground plane as shown in the
BL&E I.R.E. paper is not the equivalent/adjusted field they measured from
the monopole heights they tested. But, as BL&E published, the groundwave
fields they measured from these real monopoles over real earth was within
several percent of that theoretical maximum, when working against 113 buried
radials each of 0.41WL -- even for the poor conductivity at/near their
antenna site.

Also, I'm speaking of sky wave. Ground reflection isn't a factor in
determining surface wave, ...

But neither theory nor practice supports this, does it? If so, then the
groundwave fields that BL&E measured at 3/10 of a mile would have been at
least 29.3% less than that theoretical maximum field, which included a
perfect (3 dB) ground reflection -- not just the several percent they
measured. And this measured performance just beyond the near field radius
has been re-proven in thousands of groundwave r.m.s. field strength
measurements of AM broadcast stations over many decades since the BL&E work.

It would be a mistake to design HF antenna systems based on optimizing
surface wave propagation as AM broadcasters do, unless you desire
communication for distances not exceeding a few miles.

Just to note that since the 1930s (at least), AM broadcasters have been
aware of the effects of the differing propagation characteristics of
groundwaves and skywaves. This is evident in the fact that most 50 kW,
fulltime, AM broadcast stations in the US use a radiator height that
minimizes the self-interference of their skywave with their groundwave, so
as to ~maximize their interference-free coverage areas when skywave
propagation occurs. The great majority of these stations use a monopole
radiator height of about 195 degrees.

RF