EME communications
Photograph by dff.jiscon Flickr.
It calculates the surface area of an imaginary sphere EME communications of radius, d, that the radio wave illuminates uniformly: Substituting F into the free-space loss formula and converting to d into km: Adding factors for reflection from the Moon results in The standard radar path link formula is basis for EME path-loss calculations After including the factor for surface reflectivity it becomes Since the diameter EME communications of the Moon is 3.5*10^6 km The formula becomes For some reason not specified, Josef has increased the loss by 3-dB producing: See Note that the distance from the Earth to the Moon varies because the orbit of the Moon is not perfectly circular, it is somewhat elliptical with a mean radius of 240,000 EME communications miles. 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. W.J.
A highlight of the celebrations EME communications was an interview via the Moon with Apollo 8 astronaut Bill Anders. 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. The use of the Moon as a passive communications satellite was proposed by Mr.
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. As the albedo of the Moon is very low (maximally 12% but usually closer to 7%), and the path loss over the 770,000 kilometre return distance is extreme (around 250 to 310 dB depending on VHF-UHF band used, modulation format and Doppler shift effects), high power (more than 100 watts) and high-gain antennas (more than 20 dB) must be used. In practice, this limits the use of this technique to the spectrum at VHF and above. The Moon must be visible in order for EME communications to be possible. To determine EME Path Loss we need to know - Free space loss from an isotropic omnidirectional antenna is described by this formula. He was also part of the backup crew for Apollo 11.
This means there is an apogee (the largest distance) and a perigee (the shortest distance). 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.
The University of Tasmania in Australia with their 26m dish was able to bounce a data signal off the surface of the Moon which was received by a large dish in the Netherlands - Dwingeloo_Radio_Observatory. It was thought that at least one voice channel would be possible. 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.
The second World Moon Bounce Day is April 17th 2010 and coincides with the landing of Apollo 13 on its 40th anniversary. (http://echoesofapollo.com/moon-bounce/) World Moon Bounce Day - Echoes of Apollo (http://www.wia.org.au/members/armag/2009/august/) Amateur Radio - August 2009 - Wireless Institute of Australia VHF UHF Microwave Doppler effect - 300 Cycles at Moonrise/set An array of 8 Yagi antennas for 144 MHz EME at EA6VQ, Balearic Islands, Spain 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 UHF EME at I2FZX, Milan, Italy . Common modulation modes utilized by amateurs are continuous wave with Morse Code, digital (JT65) and when the link budgets allow, voice. 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. World Moon Bounce Day, June 29 2009, was created by Echoes of Apollo and celebrated world wide as an event preceding the 40th anniversary of the Apollo 11 Moon landing.
All amateur frequency bands from 50 MHz to 47 GHz have been used successfully, but most EME communications are on the 144, 432, or 1296 MHz bands. World Moon Bounce Day 2010 is set to precede the Apollo 13 mission sometime in early 2010.
EME presents significant challenges to amateur operators interested in working weak signal communications. Currently, EME provides the longest communications path any two stations on Earth can utilize for bi-directional communications. Amateur operations use VHF, UHF and microwave frequencies.
DeWitt as part of Project Diana.
