Line Of Sight Propagation For AM signals ?
 

matt weber wrote:

Actually the MUF (maxiumum usable frequency) is the highest frequency
that propogates beyond line of sight, and the MUF is rarely beyond
about 30Mhz. On very rare occaisons it can get as high as about
60Mhz, but I don't think there is any record of it ever getting beyond
60 Mhz.

At the peak of the sunspot cycle the MUF is often above 30-Mhz in the
daytime for weeks or months. It's not that rare to reach 40-mhz when the
solar flux is close to 300.