I have a long mental list of things I want to do when I finally get a “real” ham radio one of these days. I recently added something I had been previously aware of, but never knew much about.
The standard mode of propagation for the VHF bands is “line-of-sight.” That is, in general, if you want to talk to someone via VHF, you need to be able to “see” them. Things like trees and buildings aren’t a problem with enough power, but you can forget going over the horizon without some sort of propagation enhancement such as “Sporadic E” or tropospheric ducting.
As meteors fly through our atmosphere and burn up, they produce ionization. As it turns out, you can bounce a VHF signal off of meteor ionization trails. These trails typically only last for a few seconds at best, but it’s long enough for stations communicating at high speeds to have a short conversation. Fortunately there are enough small meteors entering the atmosphere that there’s no need to track them or anything. You just aim a directional antenna at the guy you want to talk to and transmit and listen on a set schedule.
Some hams use voice or morse code for these sorts of communications, but a more surefire way is to use a high speed digital mode, such as FSK441, a digital mode written specifically for meteor scatter communications by Joe Taylor, K1JT, a ham and a Nobel laureate in Physics. The most popular ham band for meteor scatter communications is the 6m band, though it’s possible on several others.
Another, similar, mode I’d like to try is EME. It’s a little further down the list though, as it requires a much more impression station, both in terms of antennas and amplifiers.