Innavigation, aradio beacon orradiobeacon is a kind ofbeacon, a device that marks a fixed location and allowsdirection-finding equipment to find relativebearing. It is a fixed-positionradio transmitter which radiatesradio waves which are received bynavigation instruments on ships, aircraft or vehicles.[1]
The beacon transmits a continuous or periodic radio signal on a specifiedradio frequency containing limited information (for example, its identification or location). Occasionally, the beacon's transmission includes other information, such astelemetric or meteorological data.
Radio beacons have many applications, including air and sea navigation, propagation research,robotic mapping,radio-frequency identification (RFID), andindoor navigation, as withreal-time locating systems (RTLS) likeSyledis orsimultaneous localization and mapping (SLAM).
The most basic radio-navigational aid used in aviation is thenon-directional beacon or NDB. It is a simple low- and medium-frequency transmitter used to locateairway intersections and airports and to conductinstrument approaches, with the use of aradio direction finder located on the aircraft. The aviation NDBs, especially the ones marking airway intersections, are gradually being decommissioned and replaced with other navigational aids based on newer technologies. Due to relatively low purchase, maintenance and calibration cost, NDBs are still used to mark locations of smalleraerodromes and important helicopter landing sites.
Marine beacons, based on the same technology and installed in coastal areas, have also been used by ships at sea.[2][3] Most of them, especially in the Western world, are no longer in service, while some have been converted totelemetry transmitters fordifferential GPS.[4]
Other than dedicated radio beacons, anyAM,VHF, orUHFradio station at a known location can be used as a beacon withdirection-finding equipment. However stations, which are part of asingle-frequency network should not be used as in this case the direction of the minimum or the maximum can be different from the direction to the transmitter site.
Amarker beacon is a specialized beacon used in aviation, in conjunction with aninstrument landing system (ILS), to give pilots a means to determine distance to the runway. Marker beacons transmit on the dedicated frequency of 75 MHz. This type of beacon is slowly being phased out, and most new ILS installations have no marker beacons.
Anamateur radio propagation beacon is specifically used to study the propagation of radio signals. Nearly all of them are part of theamateur radio service.
A group of radio beacons with single-letter identifiers ("C", "D", "M", "S", "P", etc.) transmitting inMorse code have been regularly reported on varioushigh frequencies. There is no official information available about these transmitters, and they are not registered with theInternational Telecommunication Union. Some investigators suggest that some of these so-called "cluster beacons" are actually radio propagation beacons for naval use.
Beacons are also used in bothgeostationary andinclined-orbit satellites. Any satellite will emit one or more beacons (normally on a fixed frequency) whose purpose is twofold; as well as containingmodulated station-keeping information (telemetry), the beacon locates the satellite (determines itsazimuth and elevation) in the sky.
A beacon was left on the Moon by crew ofApollo 17, the last Apollo mission, transmittingFSK telemetry on 2276.0 MHz[5]
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Driftnet radio buoys are extensively used by fishing boats operating in open seas and oceans.[6] They are useful for collecting long fishing lines or fishing nets, with the assistance of aradio direction finder. According to product information released by manufacturer Kato Electronics Co, Ltd., these buoys transmit on 1600–2850 kHz with a power of 4-15 W.
Some types of driftnet buoys, called "SelCall buoys", answer only when they are called by their own ships. Using this technique the buoy prevents nets and fishing gears from being carried away by other ships, while the battery power consumption remains low.[7]
Distress radio beacons, also collectively known asdistress beacons,emergency beacons, or simplybeacons, are portable, battery-poweredradio transmitters carried by ships, aircraft, hikers or cross-country skiers, used in emergencies tolocate people in need of immediate rescue. In the event of an emergency, such as an aircraft crashing, ship sinking, or a hiker or skier becoming injured or lost, the transmitter is activated and begins transmitting a continuousdistress radio signal, which is used bysearch-and-rescue teams to quickly locate the emergency and render aid. The basic purpose of distress radio beacons is to rescue people within the so-called "golden day" (the first 24 hours following a traumatic event), when the majority of survivors can still be saved.[8]
There are three kinds of distress radio beacons:
The largest distress beacon system is the internationalCospas-Sarsat search and rescue satellite system. Consisting of about 67 Earth-orbitingsatellites carryingtransponders and signal processors operated by 45 member nations, it can determine thelocation anywhere on Earth of a distress beacon transmitting on the Cospas-Sarsat distress frequency of 406 MHz. When it detects a beacon, the Cospas-Sarsat system calculates its location and quickly forwards the information to the localsearch and rescue (SAR) authorities, who find the emergency and perform the rescue. Cospas beacons also radiate a 121.5 MHz homing signal used by SAR teams withdirection finding equipment to home in on the location. With first generation beacons, the satellites are able to locate the beacon with an accuracy of about 2 km (1.2 mi). However the latest generation of beacons, calledemergency position-indicating radiobeacons (EPIRB or GPIRB) carryGPS and transmit their location to within about 100 meters.
In the field ofWi-Fi (wireless local area networks using the IEEE 802.11b and 802.11g specification), the termbeacon signifies a specific data transmission from thewireless access point (AP), which carries theSSID, the channel number and security protocols such asWired Equivalent Privacy (WEP) orWi-Fi Protected Access (WPA). This transmission does not contain the link layer address of another Wi-Fi device, therefore it can be received by any LAN client.[9]
Stations participating in packet radio networks based on theAX.25 link layer protocol also use beacon transmissions to identify themselves and broadcast brief information about operational status. The beacon transmissions use specialUI orUnnumbered Information frames, which are not part of a connection and can be displayed by any station.[10][11] Beacons in traditional AX.25 amateur packet radio networks contain free format information text, readable by human operators.
This mode of AX.25 operation, using a formal machine-readable beacon text specification developed by Bob Bruninga, WB4APR, became the basis of theAPRS networks.
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