Moon bounce

Moon bouncing is a technique that has been used for decades by radio amateurs to make connections via the Moon by using it as a mirror for radio waves. They do this on frequencies and at distances where it is normally not possible to make a radio connection with other radio amateurs.

Of course, the Moon is not an ideal mirror. The Moon absorbs about 93% of the radio signal. The remaining 7% reflected by the Moon goes in all directions. The Moon has no smooth surface so the reality is even worse. Only a small fraction of that 7% reaches the earth. For a dish antenna like the 25 meter Dwingeloo Radio Telescope the total attenuation of the captured radio signal is about 270 dB (Decibel). That is a weakening of 0.000 000 000 000 000 000 000 000 001 (26 times a ‘0’ behind the decimal point and a ‘1’ at the 27th position) compared to the strength of the original radio signal.

– Product of the Cold War

Project Diana Moon Radar QSL card

The technology to send radar waves to the Moon and to catch them was successfully developed shortly after the Second World War by the United States Army Signal Corps (USASC). In this Diana project they wanted to demonstrate that with this technique the army could detect and follow enemy missiles. The Diana project is often seen as the beginning of new forms of space research: radio communication with satellites and spaceships and radar research of planets, moons and asteroids.

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Radio amateurs use this technique of radio connection via the Moon – also called Earth-Moon-Earth connection (EME) – to make contact with fellow radio amateurs that they normally cannot reach because their station is behind the horizon. For this, they use Morse code and with sufficiently large antennas and powerful transmitters and receivers, it is even possible to make contact by voice.