An Emergency Position Indicating RadioBeacon (EPIRB) is a device used in the maritime sector to alert rescue authorites and indicate the location and the identity of a vessel in distress. When activated, the EPIRB starts to emit a signal that is detectable by the COSPAS-SARSAT satellite network anywhere in the world. The network passes the alert to the nearest rescue authority.
Most EPIRB's operate in the 406 MHz band. There are two types of 406 MHz EPIRB's. A category I EPIRB is automatically activated when a ship sinks. These category I EPIRBs are housed in a special bracket equiped with a hydrostatic release. This mechanism releases the EPIRB at a water depth of 1 - 3 meter. The EPIRB floats to the surface and starts transmitting. Category I EPIRBS can also be activated manually.
A category II EPIRB has to be activated manually.
|A 406 MHz EPIRB.|
The satellite system can detect the location of the EPIRB with an accuracy of 2 to 5 km. There are also 406 MHz EPIRB's available with an integrated GPS navigation receiver. These EPIRB's will transmit an accurate location.
Both categories of the 406 MHz EPIRBs also transmit a low-power (0,25 W) "homing" signal on 121.5 MHz. This allows rescue forces to home in on a beacon as soon as they are in the vicinity.
An 406 MHz EPIRB transmits a 5 W signal once every 50 seconds. The message is either a "short message" of 122-bit in length or a "long message" of 144-bit in length. Both messages contain a 49 bit field for identification and position information. The MMSI number is used to identify the vessel in distress.
The 406 MHz channel is 170 kHz wide with a center frequency at 406.05 MHz.
A 406 MHz EPIRB is part of the requirements for GMDSS.
Older types of EPIRB's use the 121,5 MHz or 243 MHz band. These were originally designed to be detected by overflying commercial or military aircrafts. Satellites were designed to detect these EPIRBs as well, but detection by satellites is limited on these frequencies. COSPAS-SARSAT announced that it will cease detection on 121,5 and 243 MHz by February 1st, 2009.
Inmarsat used to have an Inmarsat E service. These EPIRB's worked on 1646 MHz. The EPIRB's were detectable by Inmarsat geostationary satellites. This service has been shut down on 1 december 2006.