EME (communications)
Encyclopedia
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.
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.
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
. 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. 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.
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 antenna
s (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. It calculates the surface area of an imaginary sphere 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 of the Moon is ≈ 3500 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 miles. This means there is an apogee (the largest distance) and a perigee (the shortest distance). In addition, the orbital plane precesses
with a principal period of 18.6 years.
Depending on the position of the Moon with respect to the Earth, Apogee can be as much as 406,700km, while Perigee can be as little as 356,400km.
(ham) operators utilize EME for two-way communications. 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. All amateur frequency bands from 50 MHz to 47 GHz have been used successfully, but most EME communications are on the 2 meter, 70-centimeter, or 23-centimeter bands. 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. A highlight of the celebrations was an interview via the Moon with Apollo 8 astronaut Bill Anders. He was also part of the backup crew for Apollo 11. 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
. The data signal was successfully resolved back to data setting a world record for the lowest power data signal returned from the Moon with a transmit power of 3 milliwatts - about 1,000th of the power of a strong flashlight filament globe. World Moon Bounce Day 2010 was set to precede the Apollo 13 mission sometime in early 2010. The second World Moon Bounce Day was April 17th 2010 and coincided 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
UHF
Microwave
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
-based transmitter directed via reflection from the surface of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
back to an Earth-based receiver.
History
The use of the Moon as a passive communications satellite was proposed by Mr. W.J. BrayJohn Bray (communications engineer)
William John Bray CBE , was a communications engineer and Director of Research at the Post Office Research Station, between 1966 and 1975.-Articles:...
of the British General Post Office
General Post Office
General Post Office is the name of the British postal system from 1660 until 1969.General Post Office may also refer to:* General Post Office, Perth* General Post Office, Sydney* General Post Office, Melbourne* General Post Office, Brisbane...
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.
The "moon bounce" technique was developed by the United States Military in the years after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, 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
Project Diana
Project Diana, named for the Roman moon goddess Diana — goddess of the hunt, wild animals and the moon — was a project of the US Army Signal Corps to bounce radio signals off the moon and receive the reflected signals...
. The Communication Moon Relay
Communication Moon Relay
The Communication Moon Relay project was a telecommunication project carried out by the United States Navy...
project that followed led to more practical uses, including a teletype link between the naval base at Pearl Harbor, Hawaii and United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
headquarters in Washington, DC. 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.
EME communications technical details
As the albedoAlbedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
of the Moon is very low (maximally 12% but usually closer to 7%), and the path loss
Path loss
Path loss is the reduction in power density of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system....
over the 770,000 kilometre
1 E8 m
To help compare different orders of magnitude, this page lists lengths starting at 108 metres .Distances shorter than 108 metres* 102 Mm — Diameter of HD 149026 b, an unusually dense Jovian planet...
return distance is extreme (around 250 to 310 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
depending on VHF-UHF band used, modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
format and Doppler shift effects), high power (more than 100 watts) and high-gain antenna
High-gain antenna
A high-gain antenna is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna...
s (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 -
- Moon distance from either the transmitting or receiving station
- Transmitter station output in watts, expressed as ERPEffective radiated powerIn radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
[roughly transmitter power output (minus feedline loss) x forward antenna gain] - Receive station gain (actual receiver gain minus feedline loss, x antenna gain)
- The operating frequency of the transmitter and receiver
Free space loss from an isotropic omnidirectional antenna is described by this formula. It calculates the surface area of an imaginary sphere of radius, d, that the radio wave illuminates uniformly:
- Loss =
where pi ≈ 3.14, d = distance and lambda = wavelength, in meters - Lambda = c/F F = Hz, c =
meters/sec. - Lambda =
when F is in MHz.
Substituting F into the free-space loss formula and converting to d into km:
- Loss =
or - Loss(dB) =
Adding factors for reflection from the Moon results in
- Loss-eme(dB) = 32.45 + 20Log(F) + 20Log(2*d) + 50.21 - 10Log(.065)
The standard radar path link formula is basis for EME path-loss calculations
-
- Loss =
After including the factor for surface reflectivity it becomes
-
-
where 
is the Moon's diameter
Since the diameter of the Moon is ≈ 3500 km
The formula becomes
- Loss-eme(dB) = 20Log(F) + 40LOG(d) - 17.49, F = MHz, d = km
For some reason not specified, Josef has increased the loss by 3-dB producing:
- Loss-eme(dB) = 103.4 + 20LOG(F) + 40LOG(d) - 10Log(rho) or
- Loss-eme(dB) = 20Log(F) + 40LOG(d) - 14.49
See
- http://www.k5rmg.org/tech/EME.html (another calculator)
- http://www.df9cy.de/tech-mat/pathloss.htm (gives formulas for EME path loss calculation)
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 miles. This means there is an apogee (the largest distance) and a perigee (the shortest distance). In addition, the orbital plane precesses
Precession
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
with a principal period of 18.6 years.
Depending on the position of the Moon with respect to the Earth, Apogee can be as much as 406,700km, while Perigee can be as little as 356,400km.
- This translates to as much as 2.25dB difference in path loss from apogee to perigee.
- The mean distance from Earth to Moon is given as 384,400km.
- These calculations consider the fact that the Moon is only 7% efficient as a reflector, use the radar equation (which defines a two-way path-loss model) and the assumption that the Moon is a spherical reflector.
Current EME communications
Amateur radioAmateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
(ham) operators utilize EME for two-way communications. 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. All amateur frequency bands from 50 MHz to 47 GHz have been used successfully, but most EME communications are on the 2 meter, 70-centimeter, or 23-centimeter bands. Common modulation modes utilized by amateurs are continuous wave
Continuous wave
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
with Morse Code, digital (JT65) and when the link budgets allow, voice.
Recent advances in digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
have allowed EME contacts, admittedly with low data rate, to take place with powers in the order of 100 Watts
Orders of magnitude (power)
This page lists examples of the power in watts produced by various sources of energy. They are grouped by orders of magnitude, and each section covers three orders of magnitude, or a factor of one thousand.-zeptowatt :...
and a single Yagi antenna
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
.
World Moon Bounce Day, June 29 2009, was created by Echoes of Apollo
Echoes of Apollo
Echoes of Apollo is an international organisation formed in January 2009 by Pat Barthelow and Robert Brand . Robert has worked on international space projects including Apollo 11 communications and Pat has limited experience with Bouncing amateur radio transmissions off the moon - EME...
and celebrated world wide as an event preceding the 40th anniversary of the Apollo 11 Moon landing. A highlight of the celebrations was an interview via the Moon with Apollo 8 astronaut Bill Anders. He was also part of the backup crew for Apollo 11. 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
Dwingeloo Radio Observatory
The Dwingeloo Radio Observatory , is a single dish radio telescope with a diameter of 25 m. Construction started in 1954, the telescope was completed in 1956. At that time it was the largest radio telescope in the world...
. The data signal was successfully resolved back to data setting a world record for the lowest power data signal returned from the Moon with a transmit power of 3 milliwatts - about 1,000th of the power of a strong flashlight filament globe. World Moon Bounce Day 2010 was set to precede the Apollo 13 mission sometime in early 2010. The second World Moon Bounce Day was April 17th 2010 and coincided 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
Modulation types and frequencies optimal for EME
VHF- CWContinuous waveA continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
- JT65AWSJT (Amateur radio software)WSJT is a computer program used for weak-signal radio communication between amateur radio operators. The program was initially written by Joe Taylor, K1JT, but is now open source and is developed by a small team...
- JT65BWSJT (Amateur radio software)WSJT is a computer program used for weak-signal radio communication between amateur radio operators. The program was initially written by Joe Taylor, K1JT, but is now open source and is developed by a small team...
UHF
- CWContinuous waveA continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
- JT65CWSJT (Amateur radio software)WSJT is a computer program used for weak-signal radio communication between amateur radio operators. The program was initially written by Joe Taylor, K1JT, but is now open source and is developed by a small team...
- SSBSingle-sideband modulationSingle-sideband modulation or Single-sideband suppressed-carrier is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth....
Microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
- CWContinuous waveA continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
- SSBSingle-sideband modulationSingle-sideband modulation or Single-sideband suppressed-carrier is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth....
Other Factors influencing EME communications
Doppler effect - 300 Hz at Moonrise/set- At Moonrise, returned signals will be shifted approximately 300 Hz higher in frequency due to the Doppler effect between the Earth and Moon.
- As the Moon traverses the sky to a point due south the Doppler effect approaches nothing. As the Moon sets, signals are shifted lower in frequency until at Moonset they are shifted 300 Hz lower.
- Doppler effects cause many problems when tuning into and locking onto signals from the Moon.
See also
- Information theoryInformation theoryInformation theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...
- Meteor burst communicationsMeteor burst communicationsMeteor burst communications , also referred to as meteor scatter communications, is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communications paths between radio stations up to apart.-How it works:As the earth moves along its...
- Passive repeaterPassive repeaterA passive radio link deflection, or passive repeater is a plant for the implementation of a microwave link, in which because of an obstacle in the signal path no direct line of sight microwave link is possible...
- Radar Equation