The 406 MHz signal is detected by multiple satellites and from that information the location of the beacon can be calculated. This data alone is sufficient for SAR to find persons or ships in distress in a reasonable timeframe. However, as a further enhancement, some beacons have a GPS engine onboard. This feature allows the beacon to acquire current location coordinates from an internal GPS receiver. The purpose of this feature is to send an even more precise location of the beacon to the satellites, i.e., latitude and longitude data. This helps SAR to reach the location even faster.
2. Internal GPS position system
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When the beacon is activated, the internal GPS immediately attempts to acquire positional coordinates. GPS coordinates can be acquired any time that the GPS is on, but only valid data is saved. Once the beacon acquires valid coordinates, the data is included as part of the next transmitted 406 MHz digital message.
The internal GPS operates on a schedule during a beacon activation. The GPS is on for a time, actively acquiring coordinates, and off for a time, in a standby state. The schedule is designed to conserve battery but, at the same time, assure that navigational coordinates are regularly updated.
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