Thanks Mike,
The critical frequency is also effectively the frequency where near straight up
the Ionosphere is for the most part transparent and non reflecting when at
lower angles like less than 20 degrees its usable for DX.
Water does the same thing, look straight down you see the bottom, look
at a shallow angle its a good reflector.
So to work close in on 40M NVIS is not the way but a good vertical
to get a good low angle ground wave is useful.
We have been below the critical frequency for many years and at it
peak it may reach 10mhz or slightly higher (solar maximum).
One of those things that shows how antennas and their composite
patterns interact with propagation to get signals out there.
Allison
