navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...

, a radio beacon or radiobeacon is a kind of

beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...

, a device that marks a fixed location and allows direction-finding equipment to find relative bearing. But instead of employing

visible light Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm ...

, radio beacons transmit

electromagnetic radiation In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength ...

in the

radio wave Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...

band. They are used for direction-finding systems on ships, aircraft and vehicles. Radio beacons transmit a continuous or periodic radio signal with limited information (for example, its identification or location) on a specified

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...

. Occasionally, the beacon's transmission includes other information, such as telemetric or meteorological data. Radio beacons have many applications, including air and sea navigation, propagation research,

robotic mapping Robotic mapping is a discipline related to computer vision and cartography. The goal for an autonomous robot is to be able to construct (or use) a map (outdoor use) or floor plan (indoor use) and to localize itself and its recharging bases or beac ...

radio-frequency identification Radio-frequency identification (RFID) uses electromagnetic fields to automatically Automatic identification system, identify and Tracking system, track tags attached to objects. An RFID system consists of a tiny radio transponder called a tag, ...

(RFID),

near-field communication Near-field communication (NFC) is a set of communication protocols that enables communication between two electronic devices over a distance of or less. NFC offers a low-speed connection through a simple setup that can be used for the boots ...

(NFC) and indoor navigation, as with

real-time locating system Real-time locating systems (RTLS), also known as real-time tracking systems, are used to automatically identify and track the location of objects or people in real time, usually within a building or other contained area. Wireless RTLS tags are ...

s (RTLS) like Syledis or

simultaneous localization and mapping Simultaneous localization and mapping (SLAM) is the computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of an Intelligent agent, agent's location within it. While this initially ap ...

(SLAM).

Types

Radio-navigation beacons

The most basic radio-navigational aid used in aviation is the

non-directional beacon A non-directional beacon (NDB) or non-directional radio beacon is a radio beacon which does not include directional information. Radio beacons are radio transmitters at a known location, used as an aviation or marine navigational aid. NDB are i ...

or NDB. It is a simple low- and medium-frequency transmitter used to locate airway intersections and airports and to conduct

instrument approach In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach to a lan ...

es, with the use of a

radio direction finder Direction finding (DF), radio direction finding (RDF), or radiogoniometry is the use of radio waves to determine the direction to a radio source. The source may be a cooperating radio transmitter or may be an inadvertent source, a natural ...

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 smaller

aerodrome An aerodrome, airfield, or airstrip is a location from which aircraft flight operations take place, regardless of whether they involve air cargo, passengers, or neither, and regardless of whether it is for public or private use. Aerodromes inc ...

s 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. Most of them, especially in the Western world, are no longer in service, while some have been converted to

telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', 'far off', an ...

transmitters for

differential GPS Differential Global Positioning Systems (DGPSs) supplement and enhance the positional data available from global navigation satellite systems (GNSSs). A DGPS can increase accuracy of positional data by about a thousandfold, from approximately to ...

. Other than dedicated radio beacons, any AM, VHF, or

UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...

radio station Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based rad ...

at a known location can be used as a beacon with direction-finding equipment. However stations, which are part of a

single-frequency network A single-frequency network or SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel. Analog AM and FM radio broadcast networks as well as digital broadcast networks can operat ...

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.

ILS marker beacons

marker beacon A marker beacon is a particular type of VHF radio beacon used in aviation, usually in conjunction with an instrument landing system (ILS), to give pilots a means to determine position along an established route to a destination such as a runwa ...

is a specialized beacon used in aviation, in conjunction with an instrument 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.

Amateur radio propagation beacons

An amateur radio propagation beacon is specifically used to study the propagation of radio signals. Nearly all of them are part of the

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

service.

Single-letter high-frequency beacons

A group of radio beacons with single-letter identifiers ("C", "D", "M", "S", "P", etc.) transmitting in

Morse code Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...

have been regularly reported on various high frequencies. There is no official information available about these transmitters, and they are not registered with the

International Telecommunication Union The International Telecommunication Union (ITU)In the other common languages of the ITU: * * is a list of specialized agencies of the United Nations, specialized agency of the United Nations responsible for many matters related to information ...

. Some investigators suggest that some of these so-called "cluster beacons" are actually radio propagation beacons for naval use.

Space and satellite radio beacons

Beacons are also used in both

geostationary A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...

and inclined-orbit satellites. Any satellite will emit one or more beacons (normally on a fixed frequency) whose purpose is twofold; as well as containing

modulated Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

station-keeping information (telemetry), the beacon locates the satellite (determines its

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

and elevation) in the sky. A beacon was left on the Moon by crew of

Apollo 17 Apollo 17 (December 7–19, 1972) was the eleventh and final mission of NASA's Apollo program, the sixth and most recent time humans have set foot on the Moon. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on the Moon, ...

, the last Apollo mission, transmitting FSK telemetry on 2276.0 MHz

Driftnet buoy radio beacons

Driftnet radio buoys are extensively used by fishing boats operating in open seas and oceans. They are useful for collecting long fishing lines or fishing nets, with the assistance of a

. 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.

Distress radio beacons

Distress radio beacons, also collectively known as distress beacons, emergency beacons, or simply beacons, are those

tracking transmitter A tracking transmitter broadcasts a radio signal which can be detected by a directional antenna (typically a Radio Direction Finder). By rotating the antenna one can determine the direction the signal lies in and of course whatever it may be attach ...

s that operate as part of the international Cospas-Sarsat

Search and Rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

system. When activated, these beacons send out a

distress signal A distress signal, also known as a distress call, is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting radio signals, displaying a visually observable item or illumination, or making a sou ...

that, when detected by non-

satellites, can be located by

triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle m ...

. In the case of 406 MHz beacons, which transmit digital signals, the beacons can be uniquely identified almost instantly (via GEOSAR), and a GPS position can be encoded into the signal (thus providing both instantaneous identification and position).

Distress signal A distress signal, also known as a distress call, is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting radio signals, displaying a visually observable item or illumination, or making a sou ...

s from the beacons are homed by

search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

(SAR) aircraft and ground search parties, who can in turn come to the aid of the concerned boat, aircraft or persons. There are three kinds of distress radio beacons: * EPIRBs (emergency position-indicating radio beacons) signal maritime distress * ELTs (emergency locator transmitters) signal aircraft distress * PLBs (personal locator beacons) are for personal use and are intended to indicate a person in distress who is away from normal emergency response capabilities (i.e. 911) 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.

Wi-Fi beacons

In the field of

Wi-Fi Wi-Fi () is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, local area networking of devices and Internet access, allowing nearby digital devices to exchange data by ...

(wireless local area networks using the IEEE 802.11b and 802.11g specification), the term ''beacon'' signifies a specific data transmission from the

wireless access point In Computer networking device, computer networking, a wireless access point (WAP) (also just access point (AP)) is a networking hardware device that allows other Wi-Fi devices to connect to a wired network or wireless network. As a standalone ...

(AP), which carries the SSID, the channel number and security protocols such as

Wired Equivalent Privacy Wired Equivalent Privacy (WEP) is an obsolete, and insecure security algorithm for 802.11 wireless networks. It was introduced as part of the original IEEE 802.11 standard ratified in 1997. The intention was to provide a level of security and pr ...

(WEP) or

Wi-Fi Protected Access Wi-Fi Protected Access (WPA) (Wireless Protected Access), Wi-Fi Protected Access 2 (WPA2), and Wi-Fi Protected Access 3 (WPA3) are the three security certification programs developed after 2000 by the Wi-Fi Alliance to secure wireless computer n ...

(WPA). This transmission does not contain the link layer address of another Wi-Fi device, therefore it can be received by any LAN client.

AX.25 packet radio beacons

Stations participating in packet radio networks based on the AX.25 link layer protocol also use beacon transmissions to identify themselves and broadcast brief information about operational status. The beacon transmissions use special UI or ''Unnumbered Information'' frames, which are not part of a connection and can be displayed by any station. 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 the APRS networks.