EPIRB - Emergency Positioning Indicating Radio Beacon

EPIRB (Emergency Position Indicating Radio Beacons) and PLB (Personal Locator Beacons) are a fast effective way of distress alerting for any kind of vessel. 

A 406MHz beacon enables the SAR (Search and Rescue) agencies to quickly and accurately identify and locate a casualty so that they can effect a successful rescue.

How do they work? 

The frequencies in the band 406.0 - 406.1 MHz are reserved for the exclusive use of distress beacons operating with satellite systems and it is on this 406 MHz frequency a distress radio beacons transmits if activated. 

  • the signal it transmits is detected by instruments on board satellites in the COSPAS-SARSAT International Satellite System for Search and Rescue. 
  • Local Users Terminals which are the ground receiving stations receive and process the satellite downlink signal, thereby generating distress alerts. 
  • the distress alerts are passed to a Mission Control Centre which 
  • relays them to the search and rescue point of contact. For a UK registered beacon this would be the National Maritime Rescue Co-ordination Centre (NMOC) at Fareham. 

The signal transmitted by the distress radio beacon includes a digital message which allows the transmission of encoded data such as the unique identifier for the beacon that transmitted the alert and if the beacon has an integral GPS, the beacon’s position.  Otherwise the beacon’s signal may need to be detected by two or three satellites before its position can be sufficiently estimated, therefore it may take longer for SAR to be initiated. 

The unique identifier links the beacon to the data held by the UK 406 MHz Beacon Registry about the vessel or person. This database is available 24/7 and gives the Rescue Co-ordination Centre critical information, such as what type of vessel is in distress.   They need to know whether they are dealing with a cruise ship carrying thousands of people, a container ship or tanker, a fishing boat or a yacht, to know what response is needed.

Text © www.rya.org.uk 

SART - Search and Rescue Transponder

A Search and Rescue Transponder (SART) is an electronic device that automatically reacts to the emission of a radar. This enhances the visibility on a radar screen. SART transponders are used to ease the search of a vessel in distress or a liferaft.

A SART has a receiver that detects the signals from X-band radars (9.2 - 9.5 GHz). If the SART detects a signal it immediately transmits twelve pulses on the same frequency. This signal is seen by the radar as "echoes" and will be displayed on the screen as a series of twelve dots with a gap of 0.6 miles between them. The first dot is at the position of the SART and the others go in a straight line towards the edge of the screen.

If the rescue vessel approaches the SART, the twelve dots will become short arcs. These arcs increase in size if the vessel gets closer. If the rescue vessel is very close, the SART will be activated permanently by the side lobes of the radar antenna. The signal of the SART will then be visible as twelve complete circles on the radar screen. This will tell the search-and-rescue team that they have more or less arrived.