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Emergency Position Indicating Radiobeacon (EPIRB); Emergency Locator Transmitter (ELT); Personal Locating Beacon (PLB)
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EPIRBs, ELTs, and PLBs are various forms of radiobeacons that are used to locate people in distress. Generally, the term EPIRB is used for maritime distress beacons, ELT refers to an aviation beacon; and PLB refers to beacons worn on individuals (for example, hikers).
The beacons normally remain silent, and are activated either manually or automatically (for example, when they detect water) in case of an emergency. Their beacon signal can then be picked up by a receiver, and used to locate the device.
The beacons operate on one or more of three worldwide frequencies: 121.5, 243, and 406 MHz. However, since Feb 1st, 2009, 121.5 and 243 MHz signals are no longer received by satellites, and can therefore be much harder (and take much longer) to locate. Newer 406 MHz beacons can be located by a variety of satellites, including the COSPAS-SARSAT system established by the U.S., Russia, Canada, and France. Some 406 MHz beacons have built-in GPS receivers, and can encode their latitude and longitude in their beacon transmission. With these types, even geostationary satellites, such as the GOES weather satellites, can relay an accurate location of the beacon to authorities.
The satellite receivers in the 406 MHz band have a bandwidth of 24 kHz. The 406 MHz beacons transmit their signals at a bit rate of 400 bps.
EPIRBs are a component of the International Maritime Organization's (IMO's) Global Maritime Distress and Safety System (GMDSS).
Galileo, the European radionavigation-satellite system, will incorporate receivers for the 406 MHz beacons, and may even be able to talk back. According to the European Space Agency, "Galileo is to play an important part of the Medium Earth Orbit Search and Rescue system (MEOSAR). Galileo satellites will be able to pick up signals from emergency beacons carried on ships, planes or persons and ultimately send these back to national rescue centres. From this, a rescue centre can know the precise location of an accident. At least one Galileo satellite will be in view of any point on Earth so near real-time distress alert is possible. In some cases, feedback could be sent back to a beacon, something which is only made possible by Galileo."
EPIRBs transmit a 0.5s burst every 50 seconds, according to the ITU. More information on the Cospas-Sarsat system is available in ITU-R Report SM.2258 (link below).
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Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 121.5 MHz | 3 kHz | EPIRB/ELT/PLB (analog, older style, no longer tracked by satellites) | - | - |
| 243 MHz | 3 kHz | EPIRB/ELT/PLB (analog, older style, no longer tracked by satellites) | - | - |
Frequency Bands |
| Band | Use | Service11 | Table |
| 406 - 406.1 MHz | EPIRB/ELT/PLB (digital) | Mobile-satellite | - |
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