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Earth–Moon–Earth communication

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 Earth-Moon-Earth is a radio communication 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 were 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. [1]

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. This was followed by 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.

EME was also in use aboard the NSA listening ship Liberty when it was attacked by the Israel Defense Forces during the Six Day War.

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

FAQ

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 309 db).

  • High power (100w+) and high gain antennas (35db+) must be used.
  • In practice, this limits the use of this technique to the spectrum at VHF and above.

Current EME communicatons

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

UHF

Micowave

  • A part of 144 MHz EME antenna array at WA6PY in California, USA
    A part of 144 MHz EME antenna array at WA6PY in California, USA
  • A dish antenna for microwave EME work at WA6PY, California, USA
    A dish antenna for microwave EME work at WA6PY, California, USA

Other uses

EME also stands for 'Electromagnetic Emissions'.

References

  1. ^ Pether, John (1998). The Post Office at War. Bletchley Park Trust. p. 25.

See also

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