Richard Harrison wrote:
Richard Fry wrote:
"Richard Clark might have allowed for systems operating above 30 MHz.,
which include several ham bands, I believe."

I believe so too.

From page 810 of Terman`s 1955 edition:
"Space-wave Propagation. At frequencies above about 30 MHz, the
ionosphere is not able to refract energy to earth,

It is comforting to note that the ancient ones were wrong about some
things. It may not happen daily, but it happens a lot at 6 meters,
often at 2 meters, and sometimes even higher.

tom
K0TAR