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

, 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 or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

, radio beacons transmit

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...

in the radio wave

band Band or BAND may refer to: Places *Bánd, a village in Hungary *Band, Iran, a village in Urmia County, West Azerbaijan Province, Iran * Band, Mureș, a commune in Romania *Band-e Majid Khan, a village in Bukan County, West Azerbaijan Province, I ...

. They are used for direction-finding systems on ships, aircraft and vehicles. Radio beacons

transmit Transmit is a file transfer client program for macOS. Developed by Panic, Transmit is shareware. After a seven-day trial period, the product can only be used for seven-minute sessions until it has been purchased. Originally built as an FTP client ...

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 ...

. Occasionally, the beacon's transmission includes other information, such as

telemetric 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'', "remote", and ...

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 b ...

, radio-frequency identification (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 4 cm (1 in) or less. NFC offers a low-speed connection through a simple setup that can be u ...

(NFC) and indoor navigation, as with real-time locating systems (RTLS) like

Syledis Syledis (SYstem LEger pour mesure la DIStance) was a terrestrial radio navigation and locating system. The system operated in the UHF segment of 420-450 MHz. It was manufactured in France by Sercel S.A., headquarters Carquefou, and was operational d ...

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 agent's location within it. While this initially appears to be a chi ...

(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 ...

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 landi ...

es, with the use of a radio 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 smaller

aerodrome An aerodrome (Commonwealth English) or airdrome (American English) 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 publ ...

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 data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...

transmitters for

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

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

radio station Radio broadcasting is transmission 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 radio ...

at a known location can be used as a beacon with direction-finding equipment.

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 runway. ...

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

instrument landing system In aviation, the instrument landing system (ILS) is a precision radio navigation system that provides short-range guidance to aircraft to allow them to approach a runway at night or in bad weather. In its original form, it allows an aircraft to ...

(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

amateur radio propagation beacon An amateur radio propagation beacon is a radio beacon, whose purpose is the investigation of the propagation of radio signals. Most radio propagation beacons use amateur radio frequencies. They can be found on LF, MF, HF, VHF, UHF, and microwav ...

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 spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...

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 method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of ...

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 is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...

. 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 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 In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...

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

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

and elevation) in the sky. A beacon was left on the moon by the last Apollo mission, transmitting

FSK FSK may refer to: * FSK (band), a German band * Federal Counterintelligence Service, (Russian ') of Russia * Fiskerton railway station, in England * Forskolin, a diterpene * Forsvarets Spesialkommando, a Norwegian special forces unit * Fort Scott M ...

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 radio direction finder. According to product information released by manufacture
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 attac ...

s that operate as part of the international

Cospas-Sarsat The International Cospas-Sarsat Programme is a satellite-aided search and rescue (SAR) initiative. It is organized as a treaty-based, nonprofit, intergovernmental, humanitarian cooperative of 45 nations and agencies (see infobox). It is dedi ...

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 artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...

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 soun ...

that, when detected by non- geostationary satellites, can be located by triangulation. In the case of 406 MHz beacons, which transmit digital signals, the beacons can be uniquely identified almost instantly (via

GEOSAR The International Cospas-Sarsat Programme is a satellite-aided search and rescue (SAR) initiative. It is organized as a treaty-based, nonprofit, intergovernmental, humanitarian cooperative of 45 nations and agencies (see infobox). It is d ...

), and a

GPS The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...

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 soun ...

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 local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wav ...

(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, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. As a standalone device, the AP may have a wired ...

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

Wired Equivalent Privacy Wired Equivalent Privacy (WEP) was a security algorithm for 802.11 wireless networks. Introduced as part of the original IEEE 802.11 standard ratified in 1997, its intention was to provide data confidentiality comparable to that of a traditional ...

(WEP) or

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

(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 AX.25 (Amateur X.25) is a data link layer protocol originally derived from layer 2 of the X.25 protocol suite and designed for use by amateur radio operators. It is used extensively on amateur packet radio networks. AX.25 v2.0 and later occupies t ...

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.