Targeting the Moon

Microwave engineers and engineers in general tend to be in their profession be cause they like technical challenges. Historically, one of the biggest challenges has been how to extend radio communications, especially at microwave frequencies, beyond the horizon. One way to achieve this end at microwaves is to bounce radio signals off the Moon. This form of propagation is known as "moonbounce" or "Earth-Moon-Earth (EME)" and is considered the ultimate in long-distance 50-MHz-and-above communications. The Moon is approximately 385,000 km (240,000 mi) from the Earth, and reflecting signals from it allows communication between any two points. Because the Moon is so far away and not a particularly good reflector (about 7% efficient), communication using it as a passive reflector is not easy and considered by many a challenge. This article will discuss EME in more detail. It will cover some of the history of this form of propagation, technical obstacles to success and their solutions, and who is using the Moon today.