On Saturday, March 7, 2015 at 6:17:18 PM UTC-6, wrote:

But they can be used likely as high as say the 40m band in some
cases. I used to have a fairly stout ground wave on 40m when I
ran a high ground plane. And I think part of that energy was acting
as a surface wave and following the curvature of the earth.
The reason I think so, is because the distances I could work with it
were a good bit farther than what I would expect with the space wave
alone.

BTW, I could have been fooled a bit by refraction.. It is possible
for the space wave to go a bit farther than actual line of sight,
being as the radio horizon is a bit farther than the visual horizon.
Sometimes as much as a third the distance farther.
So it's hard to tell for sure which was which on 40m..
True surface wave propagation is great on MW in the daytime..
Night too, except that it's covered up by skywave clutter.. :/
My MW loops were good for receiving that, and I could totally null
out a ground/surface wave signal if I felt so compelled.