Tuesday, May 29, 2007

Moon Bounce or EME

It wasn't as as climactic as the moon landing, but still signifigant in radio land. The technique is known today as Earth-Moon-Earth (EME) or moonbounce. Signals of very high power are transmitted from antennas pointed at the moon 238,000 miles away. The moon reflects some of the signal and bounces the radio waves back to Earth to be received by listeners about 2.7 seconds later. The moon only reflects back about 7 % of the signal during a Moonbounce so this is harder than it sounds.

On January 10, 1946 , John H. DeWitt Jr. of the US Army Signal Corps bounced a 112 MHz (2.6 meters) radar beam off the moonThis was the first EME transmission. John was from Nashville and had been a Ham since 1921. He joined the US Army Electronic Branch in 1942. Two years later, he became director of the Evans Signal Laboratory at Belmar, New Jersey.

He actually beat out another radioman trying for the same acheivement in Hungary. Zoltan Bay suceeded in his first EME a mere two weeks later with radar of 2.5 m on february 6th. The first scientifically useful radar echoes, however, were those made by Frank Kerr and Shain. On November 1947. Kerr, shain and the crew at CSIRO demonstrated with a 15m echo that the short period variations of Earths rotation were caused by the vibration of the moon.
DeWitt just took that eperience and developed radar for locating mortars and directing counterfire. http://www.elite.net/~k7xq/eme.html He later returned to Nashville and broadcasting, eventually becoming president of commercial radio station WSM.