Also known as: EPIRB, 406 MHz EPIRB
An EPIRB (Emergency Position-Indicating Radio Beacon) operating on 406 MHz is a maritime distress transmitter that, once activated, sends a coded digital burst to the Cospas-Sarsat satellite constellation to summon rescue and identify the vessel in trouble. The burst carries a registered beacon identity and, in GPS-equipped units, a position, so a rescue coordination centre knows who is in distress and where almost immediately.1 A 406 MHz EPIRB is the satellite backbone of maritime distress alerting, working alongside DSC and other GMDSS elements.
Overview
Each 406 MHz beacon is programmed with a unique 15-character hexadecimal identity tied to a national registration database, which links the beacon to a specific vessel, owner, and emergency contacts. When activated — manually or automatically on immersion — the EPIRB transmits a short digital message roughly every 50 seconds. Modern beacons embed an internal GNSS receiver so the message includes a precise position; even without it, satellites can locate older beacons by Doppler processing. A low-power 121.5 MHz signal is also radiated so rescuers can home in over the final distance.
Technical characteristics
| Property | Value |
|---|---|
| Alert frequency | 406.0–406.1 MHz |
| Homing frequency | 121.5 MHz |
| Message | 15-hex-character beacon ID, optional encoded position |
| Modulation | Phase-modulated (biphase) digital burst |
| Repetition | ~50 s |
| System | Cospas-Sarsat satellites |
History
The analog 121.5 MHz distress beacon came first but suffered false alerts and poor location accuracy. The digital 406 MHz beacon, with its registered identity and stronger coding, was introduced through the Cospas-Sarsat programme; satellite processing of the 121.5 MHz channel was discontinued in 2009, leaving 406 MHz as the sole satellite-alerting frequency. EPIRBs are the maritime member of a family that also includes aviation ELTs and personal PLBs.
Deployment
Required on SOLAS vessels and carried voluntarily on many smaller craft, EPIRBs are a mandated part of GMDSS. The same 406 MHz infrastructure serves aviation and land beacons, and it interlocks with an emergency-call response chain of rescue coordination centres.
Decoding it with GopherTrunk
GopherTrunk does not decode 406 MHz EPIRB bursts. It is a land-mobile trunking scanner, and EPIRB is a specialised safety-of-life signal that should never be transmitted except in genuine distress; casual decoding is out of GT’s scope and, for live beacons, a matter for the official Cospas-Sarsat system rather than hobby receivers.
Sources
-
Emergency position-indicating radiobeacon — Wikipedia, for the 406 MHz EPIRB distress function, Cospas-Sarsat satellite alerting, registered beacon identity, GPS position encoding, and the 121.5 MHz homing signal. ↩