The COSPAS-SARSAT System uses 4 satellites at a height of about 1000 km, in near-polar orbits, and operated jointly by the USSR (COSPAS) and an AmericaniCanadianlFrench consortium (SARSAT). Together the satellites scan every part of the earth 's surface every 2-3 hours and receive signals from EPIRB s on 406 MHz and 121.5 MHz .

Local User Terminal (LUT) In over 20 countries there are a number of ground stations known as Local User Terminals or LUTs, which track the satellites and receive information from them as they pass overhead. EPIRB signals received at the satellite exhibit a frequency shift known as Doppler Effect. This information is relayed to the LUT where it is computer analysed and related to the satellite position, which is always precisely known. The EPIRB position can then be accurately determined.