What's the difference between 406MHz EPIRBs and the new GPIRB?
The position of a 406 MHz EPIRBs is determined by calculations using the Doppler shift in the beacon's distress signal, which occurs as satellites approach and recede in overhead orbits. The accuracy of the calculations is determined by the number of signal bursts received by the satellites. Accuracy is enhanced when a satellite passes directly overhead, because the satellite receives the greatest number of signal bursts. The only real problem with the system is that it takes time for an accurate fix to be acquired.
In contrast, the GPIRB (combined GPS EPIRB) takes an active role in determining its own position. When activated, its internal GPS finds its own position, just like an onboard GPS you might already have. Having located itself, it broadcasts its identity and position on 406MHz. It will then shut down for 20 minutes to conserve power, and repeat the process of locating itself and broadcasting. It will continue to update its position every 20 minutes as long as it is active.
The advantage of a GPIRB is that an accurate fix is almost instantly available; its frequent update allows rescuers to compute drift accurately, and direct SAR teams directly to you -- difficult to do with the time delays of an EPIRB.
Class B: Transmits on Civilian (121.5 MHz) and Military (243.0 MHz) rescue frequencies. These units do not require registration
Class 406: Transmits on COSPAS-SARSAT (406 MHz) rescue frequency to orbiting satelites. 406 EPIRBS must be registered with the FCC and provide the best response time available!