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Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
In navigation, a radio beacon or radiobeacon is a kind of beacon, a device that marks a fixed location and allows direction-finding equipment to find relative bearing. It is a fixed-position radio transmitter which radiates radio waves which are received by navigation instruments on ships, aircraft or vehicles.[1]
The beacon transmits a continuous or periodic radio signal on a specified radio frequency containing limited information (for example, its identification or location). 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, radio-frequency identification (RFID), and indoor navigation, as with real-time locating systems (RTLS) like Syledis or simultaneous localization and mapping (SLAM).
The most basic radio-navigational aid used in aviation is the non-directional beacon or NDB. It is a simple low- and medium-frequency transmitter used to locate airway intersections and airports and to conduct instrument approaches, 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 aerodromes 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 to telemetry transmitters for differential GPS.[4]
Other than dedicated radio beacons, any AM, VHF, or UHF radio station at a known location can be used as a beacon with direction-finding equipment. However stations, which are part of a single-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.
A marker beacon 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.
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 service.
A group of radio beacons with single-letter identifiers ("C", "D", "M", "S", "P", etc.) transmitting in Morse code 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. Some investigators suggest that some of these so-called "cluster beacons" are actually radio propagation beacons for naval use.
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 station-keeping information (telemetry), the beacon locates the satellite (determines its azimuth and elevation) in the sky.
A beacon was left on the Moon by crew of Apollo 17, the last Apollo mission, transmitting FSK telemetry on 2276.0 MHz[5]
![[icon]](viewer.php?source=wikipedia&q=File%3AWiki%20letter%20w%20cropped.svg&result=0#selected-result){kind=small} | This section needs expansion. You can help by adding missing information. (June 2008) |
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 a radio 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 as distress beacons, emergency beacons, or simply beacons, are portable, battery-powered radio transmitters carried by ships, aircraft, hikers or cross-country skiers, used in emergencies to locate 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 continuous distress radio signal, which is used by search-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 international Cospas-Sarsat search and rescue satellite system. Consisting of about 67 Earth-orbiting satellites carrying transponders and signal processors operated by 45 member nations, it can determine the location 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 local search 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 with direction 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, called emergency position-indicating radiobeacons (EPIRB or GPIRB) carry GPS and transmit their location to within about 100 meters.
In the field of Wi-Fi (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 (AP), which carries the SSID, the channel number and security protocols such as Wired Equivalent Privacy (WEP) or Wi-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 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.[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 the APRS networks.
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder called a tag, a radio receiver, and a transmitter. When triggered by an electromagnetic interrogation pulse from a nearby RFID reader device, the tag transmits digital data, usually an identifying inventory number, back to the reader. This number can be used to track inventory goods. Passive tags are powered by energy from the RFID reader's interrogating radio waves. Active tags are powered by a battery and thus can be read at a greater range from the RFID reader, up to hundreds of meters. Unlike a barcode, the tag does not need to be within the line of sight of the reader, so it may be embedded in the tracked object. RFID is one method of automatic identification and data capture (AIDC). RFID tags are used in many industries. For example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line, RFID-tagged pharmaceuticals can be tracked through warehouses, and implanting RFID microchips in livestock and pets enables positive identification of animals. Tags can also be used in shops to expedite checkout, and to prevent theft by customers and employees. Since RFID tags can be attached to physical money, clothing, and possessions, or implanted in animals and people, the possibility of reading personally linked information without consent has raised privacy concerns. These concerns resulted in standard specifications development addressing privacy and security issues. In 2014, the world RFID market was worth US$8.89 billion, up from US$7.77 billion in 2013 and US$6.96 billion in 2012. This figure includes tags, readers, and software/services for RFID cards, labels, fobs, and all other form factors. The market value is expected to rise from US$12.08 billion in 2020 to US$16.23 billion by 2029. In 2024, about 50 billion tag chips were sold, according to Atlas RFID and RAIN Alliance webinars in July 2025.
Various schools have been using radio-frequency identification technology to record and monitor students.
In navigation, a radio beacon or radiobeacon is a kind of beacon, a device that marks a fixed location and allows direction-finding equipment to find relative bearing. It is a fixed-position radio transmitter which radiates radio waves which are received by navigation instruments on ships, aircraft or vehicles. The beacon transmits a continuous or periodic radio signal on a specified radio frequency containing limited information (for example, its identification or location). 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, radio-frequency identification (RFID), and indoor navigation, as with real-time locating systems (RTLS) like Syledis or simultaneous localization and mapping (SLAM).
Automatic identification and data capture (AIDC) refers to the methods of automatically identifying objects, collecting data about them, and entering them directly into computer systems, without human involvement. Technologies typically considered as part of AIDC include QR codes, barcodes, radio-frequency identification (RFID), biometrics (like iris and facial recognition system), magnetic stripes, optical character recognition (OCR), smart cards, and voice recognition. AIDC is also commonly referred to as "Automatic Identification", "Auto-ID" and "Automatic Data Capture". AIDC is the process or means of obtaining external data, particularly through the analysis of images, sounds, or videos. To capture data, a transducer is employed which converts the actual image or a sound into a digital file. The file is then stored and at a later time, it can be analyzed by a computer, or compared with other files in a database to verify identity or to provide authorization to enter a secured system. Capturing data can be done in various ways; the best method depends on application. In biometric security systems, capture is the acquisition of or the process of acquiring and identifying characteristics such as finger image, palm image, facial image, iris print, or voiceprint which involves audio data, and the rest all involve video data. Radio-frequency identification is relatively a new AIDC technology, which was first developed in the 1980s. The technology acts as a base in automated data collection, identification, and analysis systems worldwide. RFID has found its importance in a wide range of markets, including livestock identification and Automated Vehicle Identification (AVI) systems because of its capability to track moving objects. These automated wireless AIDC systems are effective in manufacturing environments where barcode labels could not survive.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
