Personal Locator Beacons PLBs and EPIRBs
Personal Locator Beacons PLBs and similarly, Emergency Position Indicating Radio Beacons EPIRBs used for maritime distress alerting, and Emergency Locator Transmitters ELTs used for aeronautical distress alerting are radio transmitting devices which operate in the 406 MHz band for sending distress alert signals to Cospas-Sarsat satellites.
The satellites relay the signals to a Ground Station and then on to the Mission Control Centre where the signal is processed for onward transmission to the Rescue Co-ordination Centre who will activate and then co-ordinate the appropriate SAR response.
The processing of the beacon signal at the Mission Control Centre determines the identity of the Beacon ie maritime or air, whom it belongs to and the location of the beacon the latter being the most important item of information. Location is determined in two ways ie if the Beacon is fitted with GPS then the position from the GPS is included in the distress alert signal or if no GPS, then the position is determined by the Doppler techniques which is complex but in simple terms is about the movement of the satellite(s) (which are polar orbiting) in relation to the stationary beacon.
Many Beacons also transmit a homing signal which help eg SAR helicopters, to home in on the beacon when approaching the position given by the Rescue Co-ordination Centre.
