406 MHz Beacons

Beacon ImageDevelopment of a new generation of beacons transmitting at 406 MHz commenced at the beginning of the Cospas-Sarsat project. The 406 MHz units were designed specifically for satellite detection and Doppler location, and provide the following:

  • improved location accuracy and ambiguity resolution;
  • increased system capacity (i.e. capability to process a greater number of beacons transmitting simultaneously in field of view of satellite);
  • increased probability of detection (higher power);
  • global coverage; and
  • unique identification of each beacon.

System performance is greatly enhanced both by the improved frequency stability of the 406 MHz units and by operation at a dedicated frequency.

These beacons transmit a 5 Watt RF burst of approximately 0.5 seconds duration every 50 seconds. The carrier frequency is very stable and is phase-modulated with a digital message. Frequency stability ensures accurate location, while the high peak power increases the probability of detection. The low duty cycle provides a multiple-access capability for a large number of beacons simultaneously operating in view of a polar orbiting satellite, and low mean power consumption.

An important feature of 406 MHz emergency beacons is the digitally encoded message, which can provide information such as the country of beacon registration and the identification of the vessel or aircraft in distress, and optionally, position data from onboard navigation equipment.

An auxiliary transmitter (homing transmitter) is usually included in the 406 MHz beacon to enable suitably-equipped SAR forces to home on the distress beacon.

To ensure that 406 MHz beacons are compatible with the Cospas-Sarsat System, detailed specifications and type approval testing standards have been adopted.

The following information is available by clicking on the appropriate hyperlink:

Coding Position Data in the 406 MHz Beacon Message (Location Protocol Beacons)

The Cospas-Sarsat specifications for 406 MHz beacons and LEOLUTs provide for optionally encoding position information in the transmitted beacon message. Beacons with this capability are referred to as location protocol beacons.

Location protocol coding schemes are available to all user categories - maritime EPIRBs, aviation ELTs, and PLBs, and are compatible with all Cospas-Sarsat satellites (geostationary (GEO) and low-altitude Earth orbiting (LEO)) and ground segment components.

Because location protocol beacons determine and transmit their location in the beacon message, they are able to provide rapid alerting and location information through the Cospas-Sarsat geostationary satellite components. Although non-location protocol beacons can provide alert information via both the GEO and LEO satellite components, they can only be located using the LEO satellite system and Doppler processing techniques.


406 MHz Beacon Reference Documents

Reference documents for the development, manufacturing and testing of 406 MHz distress beacons are: