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 Previous: Surfin': Were You A WPE? |  Next: Low Power, Crummy Antenna |
By Anthony R. Curtis, K3RXK
Contributing Editor
January 21, 2002
On January 10, 1946 ,a radio amateur in the US Army Signal Corps bounced a radar beam off the moon, marking the first Earth-Moon-Earth transmission. Amateurs using EME today continue to explore the boundaries of radio technology, and its popularity continues to grow.
 W5UN's QSL card shows his 2 meter "Mighty Big Array." [Photo courtesy W5UN] |
Earth's natural satellite, the moon, has been used for communications as a passive radio signal reflector many times in recent decades. However, before 1946, no one knew if radio waves could pass through Earth's ionosphere. Wondering if missiles could be detected above the ionosphere by radio means, the Pentagon ordered Project Diana--named after the mythical Roman moon goddess.
John H. DeWitt Jr of Nashville became an Amateur Radio operator in 1921, at the age of 15. He built his town's first broadcasting station in 1922. By 1940, he was using a radiotelescope to tune in natural radio noise generated by the Milky Way galaxy.
DeWitt joined the US Army Electronic Branch
in 1942. Two years later, he became director of the Evans Signal Laboratory at
Belmar, New Jersey, and went to work on Project Diana. Among his early
accomplishments in the Army, DeWitt developed radar for locating mortars and
directing counterfire.
 The modest moonbounce antenna at SM2CEW. [Photo courtesy of SM2CEW] |
Awaiting discharge following World War II, DeWitt was a lieutenant colonel assigned to the Signal Corps Laboratories in Ft Monmouth, New Jersey. He and his Project Diana team got the okay from the War Department to investigate the possibilities of bouncing a radio signal off the moon.
The project's radar gear was quite different
from common radio equipment of that time. It had a big antenna composed of 64
small antennas that could be pointed over the Atlantic Ocean toward the rising
moon. DeWitt found success on January 10, 1946, when the 112-MHz radar signal
from the Signal Corps' 3000-W transmitter reached the moon, and he was able to
detect its faint reflection coming back to Earth. The Earth-Moon-Earth
round-trip time was clocked at 2.56 seconds.
 The SM2CEW VHF-UHF station. [Photo courtesy of SM2CEW] |
The event was trumpeted in the news media of the day as a major achievement, proving that radio waves could penetrate Earth's atmosphere.
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. The moon acts like a giant radio mirror in the sky, bouncing the radio waves back to Earth to be received by listeners.
DeWitt later returned to Nashville and broadcasting, eventually becoming president of commercial radio station WSM. Some 53 years after making radio history, DeWitt died in January 1999 at his home in Nashville at age 92. His Amateur Radio call sign was N4CBC.
 The antenna of Scottish moonbouncer David Anderson, GM4JJJ. [Photo courtesy of GM4JJJ] |
The first Amateur Radio signals to echo from the moon were transmitted in 1953. Ross Bateman, W4AO, and William L. Smith, W3GKP, bounced 144-MHz signals off the moon.
EME today is an increasingly popular Amateur Radio operating mode among VHF and UHF enthusiasts. Radio amateurs regularly beam signals to the moon, with their reflections painting a large area of our planet.
 The GM4JJJ QSL card. [Photo courtesy of GM4JJJ |
The ham who engineered the first Amateur Radio EME contact in 1960 with hams on the East Coast -- Orrin "Hank" Brown, W6HB -- also died in January 1999, in California. Brown also was 92.
Brown had been licensed since 1923 and was an ARRL member nearly 50 years. He, too, had worked in commercial radio, at stations KPO and KSBR. Later, he worked at Eitel-McCullough and served as Eimac's marketing director for 20 years. He was a founding member of Project OSCAR and a project leader for OSCAR-3, the first real-time repeater satellite of any type.
The state of the art today is being pushed by VHF-UHF and microwave enthusiasts such as Al Ward, W5LUA, of Allen, Texas. Ward, the recipient of the 2000 ARRL Microwave Development Award, in 2001 documented echoes from the moon on 24 GHz while running 20 W to a 3-meter dish. The reception was particularly significant because water-vapor absorption of signals peaks at around 24 GHz.
The ARRL's "Introduction to Moonbounce" page includes a link to the July 1985 QST article "A Basic Approach to Moonbounce," available as an Adobe PDF file.
 SETI League President Richard Factor, WA2IKL, visits the Arecibo Observatory in Puerto Rico in March, 2000. [Photo courtesy of WA2IKL and the SETI League] |
Hundreds of Amateur Radio operators have been introduced to EME during the past 40 years, according to the nonprofit SETI League, as several of the world's largest radiotelescopes have been used to reflect microwave signals off the lunar surface.
Radio amateurs at the SETI League returned the favor in 2001 by providing astronomers at the Arecibo Observatory in Puerto Rico with a highly stable, precisely calibrated moonbounce signal with which to test their equipment.
 An image of the Pioneer 10 beacon, as received by Project Phoenix a few years ago, when the spacecraft was about 8 billion km from Earth. Today, at a distance of 11 billion km, the weak beacon is beyond range of even our best SETI telescopes. [Photo courtesy of SETI League] |
SETI League president Richard Factor, WA2IKL, visited Arecibo in 2000 and discovered that the microwave beacon on the Pioneer 10 deep space probe, long used by radio astronomers to calibrate their equipment, no longer could be detected on Earth. The SETI League then began providing a replacement beacon, by bouncing microwave signals off the surface of the moon.
The SETI League project is known as "Lunar Reflective Calibration Beacon for Radio Astronomy." Its beacon on 1296 MHz, operated by WA2IKL at Kinnelon, New Jersey, transmits on a five-minute repeating cycle, beginning on the hour, whenever the moon is above the New Jersey horizon.
 The snow and ice-encased SETI beacon antenna following a March 2001 blizzard in the northeastern US. [Photo courtesy of SETI League |
Meanwhile, Peter Sundberg, SM2CEW, of Luleå, Sweden, uses QRP to, as he says, "get on the moon" with a relatively tiny homebrewed 7-element beam just 3 meters long and only 3 meters above the ground.
Want to hear what it sounds like? Mike Cook, AF9Y, of Huntertown, Indiana, offers typical moonbounce audio recordings on his EME page, along with a prize for decoding an extremely weak signal. Leif Aringsbrink, SM5BSZ, also has audio recordings on his Web site.
N1BUG explains EME operating techniques on his N1BUG Web page. W6/PA0ZN displays a gallery of the EME antenna arrays from the "432 MHz and Above Newsletter" as well as a discussion of sky noise and other technical issues.
 This waterfall display shows the Doppler-shifted SETI League EME beacon as received by the Arecibo radio telescope. The signal was pulled out from 22 dB below the receiver's noise level as the beacon illuminated the moon at a power level of a mere 10 W. [Photo courtesy of SETI League] |
How about getting on the moon? If your 2-meter transmitter delivers 100 W to a 16-element Yagi and your receiver front end has reasonably low noise, you may be able to work Dave Blaschke, W5UN, via 2-meter moonbounce on 144.041 MHz CW. E-mail him to set up an EME schedule.
The work that a ham started with the first Earth-Moon-Earth transmission 56 years ago continues to push the technology envelope in the 21st century.
Editor's note:
ARRL Life Member Anthony R. Curtis, K3RXK, lives in Florence, Kentucky. He
describes himself as "a dc-to-daylight kind of guy" interested in AMSAT, TAPR,
ARES, HF, VHF, UHF, digital, CW, SSB, FM, QRP, contesting and DX. Licensed
since 1954, he originally held the call sign W8TIZ. An Extra class op with a
PhD in mass communication, Curtis has written 72 books about space, astronomy,
computers and electronics. He is editor of Space Today Online. Active as an ARRL
field volunteer, Curtis served as Section Emergency Coordinator for the
Maryland-DC Section and as net manager for the Maryland Emergency Phone Net. He
now serves as an ARRL Educational Advisor and a Great Lakes Division Assistant
Director. He also has been president of clubs and repeater associations. Curtis
is employed as associate dean for academic information services at the Union
Institute & University in Cincinnati, Ohio. He is a NASA Solar System
Ambassador and an Apple Distinguished Educator. Readers can contact Tony Curtis
via e-mail.
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