C/S G.003 - INTRODUCTION TO THE COSPAS-SARSAT SYSTEM Issue 7

Each LUT continually monitors the Cospas-Sarsat downlink signals for the presence of any message from a 406 MHz distress beacon. As each such message is detected, the LUT extracts the message and decodes the binary data that it contains. The LUT also calculates and records the frequency and the time at which the message is received at the satellite.

 Because each satellite system is at a different altitude, each one has a different ability to detect the beacon signals. For example, the GEOSAR satellites are much further away from the beacons than the LEOSAR or MEOSAR satellites, so the quality of the received signal is not as good. To enhance the quality of the received signal, the GEOLUT may integrate the data from two (or more) successive transmissions to extract the beacon message. When a LUT does not have enough data to determine an location for any beacon, it will generate an unlocated alert message for its associated MCC.