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Meteor burst communications (MBC), also referred to as meteor scatter communications, [1] 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 2,250 kilometres (1,400 mi) apart. There can be forward-scatter or back-scatter of the radio waves.
As the Earth moves along its orbital path, millions of particles known as meteoroids enter the Earth's atmosphere every day, a small fraction of which have properties useful for point-to-point communication. [2] When these meteoroids begin to burn up, they create a glowing trail of ionized particles (called a meteor) in the E layer of the atmosphere that can persist for up to several seconds. The ionization trails can be very dense and thus used to reflect radio waves. The frequencies that can be reflected by any particular ion trail are determined by the intensity of the ionization created by the meteor, often a function of the initial size of the particle, and are generally between 30 MHz and 50 MHz. [3]
The distance over which communications can be established is determined by the altitude at which the ionization is created, the location over the surface of the Earth where the meteoroid is falling, the angle of entry into the atmosphere, and the relative locations of the stations attempting to establish communications. Because these ionization trails only exist for fractions of a second to as long as a few seconds, they create only brief windows of opportunity for communications.[ citation needed ]
The earliest direct observation of interaction between meteors and radio propagation was reported in 1929 by Hantaro Nagaoka of Japan. In 1931, Greenleaf Pickard noticed that bursts of long-distance propagation occurred at times of major meteor showers. At the same time, Bell Labs researcher A. M. Skellett was studying ways to improve night-time radio propagation, and suggested that the oddities that many researchers were seeing were due to meteors. The next year Schafer and Goodall noted that the atmosphere was disturbed during that year's Leonid meteor shower, prompting Skellett to postulate that the mechanism was reflection or scattering from electrons in meteor trails. In 1944, while researching a radar system that was "pointed up" to detect the V-2 missiles falling on London, James Stanley Hey confirmed that the meteor trails were in fact reflecting radio signals.
In 1946 the US Federal Communications Commission (FCC) found a direct correlation between enhancements in VHF radio signals and individual meteors. Studies conducted in the early 1950s by the National Bureau of Standards and the Stanford Research Institute had limited success at actually using this as a medium.[ citation needed ]
The first serious effort to utilize this technique was carried out by the Canadian Defence Research Board in the early 1950s.[ citation needed ] Their project, "JANET" (named for Janus, who looked both ways), sent bursts of data pre-recorded on magnetic tape from their radar research station in Prince Albert, Saskatchewan to Toronto, a distance exceeding 2,000 km. A 90 MHz "carrier" signal was monitored for sudden increases in signal strength, signalling a meteor, which triggered a burst of data. The system was used operationally starting in 1952, and provided useful communications until the radar project was shut down around 1960.[ citation needed ]
One of the first major deployments was "COMET" (COmmunication by MEteor Trails), used for long-range communications with NATO's Supreme Headquarters Allied Powers Europe headquarters. COMET became operational in 1965, with stations located in the Netherlands, France, Italy, West Germany, the United Kingdom, and Norway.[ citation needed ] COMET maintained an average throughput between 115 and 310 bits per second, depending on the time of year.[ citation needed ]
Meteor burst communications faded from interest with the increasing use of satellite communications systems starting in the late 1960s. In the late 1970s it became clear that the satellites were not as universally useful as originally thought, notably at high latitudes or where signal security was an issue. For these reasons, the U.S. Air Force installed the Alaska Air Command MBC system in the 1970s, although it is not publicly known whether this system is still operational.[ citation needed ]
A more recent study is the Advanced Meteor Burst Communications System (AMBCS), a testbed set up by SAIC under DARPA funding. Using phase-steerable antennas directed at the proper area of the sky for any given time of day, in the direction where the Earth is moving "forward", AMBCS was able to greatly improve the data rates, averaging 4 kilobits per second (kbit/s). While satellites may have a nominal throughput about 14 times as great,[ citation needed ] they are vastly more expensive to operate.
Additional gains in throughput are theoretically possible through the use of real-time steering. The basic concept is to use backscattered signals to pinpoint the exact location of the ion trail and direct the antenna to that spot, or in some cases, several trails simultaneously. This improves the gain, allowing much improved data rates. To date,[ when? ] this approach has not been tried experimentally, so far as is known.[ citation needed ]
The United States Department of Agriculture (USDA) used meteor scatter extensively in its SNOTEL system for over 40 years, but discontinued this use in 2023. [ citation needed ] Over 900 snow water content gauging stations in the Western United States were equipped with radio transmitters that relied upon meteor-scatter communications to send measurements to a data center. [4] [5]
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Most meteor-scatter communication is conducted between radio stations that are engaged in a precise schedule of transmission and reception periods. Because the presence of a meteor trail at a suitable location between two stations cannot be predicted, stations attempting meteor-scatter communications must transmit the same information repeatedly until an acknowledgement of reception from the other station is received. Established protocols are employed to regulate the progress of information flow between stations. While a single meteor may create an ion trail that supports several steps of the communication protocol, often a complete exchange of information requires several meteors and a long period of time to complete.
Any form of communications mode can be used for meteor-scatter communications. Single sideband audio transmission has been popular among amateur radio operators in North America attempting to establish contact with other stations during meteor showers without planning a schedule in advance with the other station. The use of Morse code has been more popular in Europe, where amateur radio operators used modified tape recorders, and later computer programs, to send messages at transmission speeds as high as 800 words per minute. Stations receiving these bursts of information record the signal and play it back at a slower speed to copy the content of the transmission. Since 2000, several digital modes implemented by computer programs have replaced voice and Morse code communications in popularity. The most popular mode for amateur radio operations is MSK144, which is implemented in the WSJT-X software.
The ionosphere is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth. It also affects GPS signals that travel through this layer.
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and 300 GHz, broadly construed. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz, or between 1 and 3000 GHz . The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range; rather, it indicates that microwaves are small, compared to the radio waves used in prior radio technology.
A transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. Signals are typically imposed on a wave of some kind suitable for the chosen medium. For example, data can modulate sound, and a transmission medium for sounds may be air, but solids and liquids may also act as the transmission medium. Vacuum or air constitutes a good transmission medium for electromagnetic waves such as light and radio waves. While a material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by absorption or reflection or refraction at the interfaces between media. Technical devices can therefore be employed to transmit or guide waves. Thus, an optical fiber or a copper cable is used as transmission media.
Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz ; above the medium frequency band (MF), to the bottom of the VHF band.
A meteoroid is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than meteoroids are classified as micrometeoroids or space dust. Many are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars.
High frequency (HF) is the ITU designation for the band of radio waves with frequency between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies can be used for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.
Tropospheric scatter, also known as troposcatter, is a method of communicating with microwave radio signals over considerable distances – often up to 500 kilometres (310 mi) and further depending on frequency of operation, equipment type, terrain, and climate factors. This method of propagation uses the tropospheric scatter phenomenon, where radio waves at UHF and SHF frequencies are randomly scattered as they pass through the upper layers of the troposphere. Radio signals are transmitted in a narrow beam aimed just above the horizon in the direction of the receiver station. As the signals pass through the troposphere, some of the energy is scattered back toward the Earth, allowing the receiver station to pick up the signal.
Anomalous propagation includes different forms of radio propagation due to an unusual distribution of temperature and humidity with height in the atmosphere. While this includes propagation with larger losses than in a standard atmosphere, in practical applications it is most often meant to refer to cases when signal propagates beyond normal radio horizon.
TV DX and FM DX is the active search for distant radio or television stations received during unusual atmospheric conditions. The term DX is an old telegraphic term meaning "long distance."
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for amateur radio communications, international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.
The 2-meter amateur radio band is a portion of the VHF radio spectrum that comprises frequencies stretching from 144 MHz to 148 MHz in International Telecommunication Union region (ITU) Regions 2 and 3 and from 144 MHz to 146 MHz in ITU Region 1 . The license privileges of amateur radio operators include the use of frequencies within this band for telecommunication, usually conducted locally with a line-of-sight range of about 100 miles (160 km).
Earth–Moon–Earth communication (EME), also known as Moon bounce, is a radio communications technique that 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.
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX).
Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections. Near-line-of-sight conditions refer to partial obstruction by a physical object present in the innermost Fresnel zone.
Amateur radio frequency allocation is done by national telecommunication authorities. Globally, the International Telecommunication Union (ITU) oversees how much radio spectrum is set aside for amateur radio transmissions. Individual amateur stations are free to use any frequency within authorized frequency ranges; authorized bands may vary by the class of the station license.
Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz of the electromagnetic spectrum. Microwave signals are normally limited to the line of sight, so long-distance transmission using these signals requires a series of repeaters forming a microwave relay network. It is possible to use microwave signals in over-the-horizon communications using tropospheric scatter, but such systems are expensive and generally used only in specialist roles.
WSJT-X 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. The digital signal processing techniques in WSJT-X make it substantially easier for amateur radio operators to employ esoteric propagation modes, such as high-speed meteor scatter and moonbounce. Additionally WSJT is able to send signal reports to spotting networks such as PSK Reporter.
This is an index to articles about terms used in discussion of radio propagation.
Airplane scattering refers to the reflection of a radio signal by the metal structure of a passing aircraft. It is observed on radio waves from high frequency to VHF through to microwaves and, besides back-scattering, yields momentary propagation up to 800 kilometers even in mountainous terrain. The most common back-scatter applications are air-traffic radar, bistatic forward-scatter guided-missile and airplane-detecting trip-wire radar, and the US space radar.
