Radio-navigation beacons 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.
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 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. 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 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.
Wi-Fi beacons 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. 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. ==See also==