EME (communications)

Earth-Moon-Earth, also known as moon bounce, is a radio communications technique which relies on the propagation of radio waves from an earth-based transmitter directed via reflection from the surface of the moon back to an earth-based receiver.

History

The use of the moon as a passive communications satellite was proposed by Mr. W. Bray of the British General Post Office in 1940. It was calculated that with the available microwave transmission powers and low noise receivers, it would be possible to beam microwave signals up from earth and reflect off the moon. It was thought that at least one voice channel would be possible. [cite book
last = Pether
first = John
title = The Post Office at War
publisher = Bletchley Park Trust
date = 1998
pages = 25 ]

The "moon bounce" technique was developed by the United States Military in the years after World War II, with the first successful reception of echoes off the moon being carried out at Fort Monmouth, New Jersey on January 10, 1946 by John H. DeWitt as part of Project Diana. [cite book
last = Butrica
first = Andrew J.
title = To See the Unseen: A History of Planetary Radar Astronomy
publisher = NASA
date = 1996
url = http://history.nasa.gov/SP-4218/ch1.htm ] The Communication Moon Relay project that followed led to more practical uses, including a teletype link between the naval base at Pearl Harbor, Hawaii and United States Navy headquarters in Washington, DC. In the days before communications satellites, a link free of the vagaries of ionospheric propagation was revolutionary.

Later, the technique was used by non-military commercial users, and the first amateur detection of signals from the moon took place in 1953.

Current EME communications

As the albedo of the moon is very low (around 12%), and the path loss over the 770,000 kilometre return distance is extreme (around 250 dB depending on VHF-UHF band used), high power (more than 100 watts) and high-gain antennas (more than 35 dB) must be used. In practice, this limits the use of this technique to the spectrum at VHF and above.

Recent advances in digital signal processing have allowed EME contacts, admittedly with low data rate, to take place with powers in the order of 100 Watts and a single Yagi antenna.

Modulation types and frequencies optimal for EME

VHF
* CW
* JT65A
* JT65B

UHF
* CW
* JT65C
* SSB

Microwave
* CW
* SSB

Gallery

References

ee also

*Information theory
*Meteor burst communications
*Passive repeater