What is ''Earth-Moon-Earth'' communications?

EME (Earth-Moon-Earth) or "moonbounce" is one of the most unusual propagation modes, but it does really work, provided you have the right equipment.

The reason we can see the Moon, obviously, is that it is reflective of the visible-light portion of the electromagnetic spectrum. But it turns out that it is reflective of RF, as well, and hams have used this property to make contacts with other similarly-equipped operators.

As you might imagine, EME is not a quick and easy mode to get involved with. It requires creating an *extremely* directional signal, with a decent amount of power to boot. An omnidirectional antenna, such as a J-Pole, would never radiate anywhere near enough of a signal to the Moon to have any hope of a readable reflected signal. EME arrays consist of phased multi-element yagi-style arrays, or large dishes, mounted on a system that allows the array to be turned to "follow" the Moon as the Earth rotates.

The Wikipedia EME article gives a nice overview of this exotic communication mode.