Radiobeacon

In navigation, an electric beacon (or electromagnetic beacon) is a kind of beacon, a device which marks a fixed location and allows direction finding equipment to find relative bearing, the direction to the beacon. The most common are radio beacons, which broadcast a radio signal which is picked up by radio direction finding systems on ships, aircraft and vehicles to determine the bearing to the beacon, but the term also covers infrared and sonar beacons.

A radio beacon is a transmitter at a known location, which transmits a continuous or periodic radio signal with limited information content (for example its identification or location), on a specified radio frequency. Occasionally the beacon function is combined with some other transmission, like telemetry data or meteorological information.

Radio beacons have many applications, including air and sea navigation, propagation research, robotic mapping, radio-frequency identification (RFID) and indoor guidance as with real-time locating systems (RTLS) like Syledis.

A most basic aviation radio navigational aid is the NDB or Non-directional Beacon. These are simple low frequency and medium frequency transmitters and they are used to locate airways intersections, 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 airways intersections, are gradually decommissioned, as they are replaced with other navigational aids based on newer technologies. Due to relatively low purchase, maintenance and calibration cost, they are still used to mark locations of smaller aerodromes and important helicopter landing sites.

There were also marine beacons, based on the same technology and installed at coastal areas, for use by ships at sea. Most of them, especially in the western world, are no longer in service, while some have been converted to telemetry transmitters for differential GPS.

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Wikipedia