I keep increasing my frequencies and want to get up the spectrum more and more. My current project is pointing a powerful focused LED from a peak and I will try to pick it up with a telescope and some sort of photo detector to receive the AM light.
I keep wondering about even higher frequencies. I am assuming Ultra violet should not be too much more difficult than Light unless the air absorbs that band.
So, going higher, could x-rays be used to communicate, maybe just CW or is it not possible at all and x-rays will not propagate.