Elta ADT406 AF/AP, User Handbook Manual

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USER’S HANDBOOK
Page 13
Oct 11/07
C. The distress frequencies
There are several advantages to using the 406 MHz frequency :
– Worldwide coverage: locating is not only possible in real-time within a radius of 2,500 km around the
station, but also in global mode outside this zone since the satellites memorize the messages on the 406
MHz frequency. Location process uses Doppler effect.
– Locating accuracy: 2 km as opposed to 10 to 15 km in the 121.5 MHz or 243 MHz frequencies. It should
be noted however that the 406 MHz beacons also transmit 121.5 MHz and 243 MHz signals which enable
the final approach of the rescue teams in homing mode.
– Information reliability: the structure of the digital signal transmitted by these beacons makes it possible to
be sure that there is actually a distress situation, as well as to identify automatically the mobile in distress
which is vital for rescue operations.
– Unique identification: each beacon has it’s own identification information.
D. ELTA and the COSPAS-SARSAT system
(1)406 MHz distress beacons:
These beacons transmit to the satellites a digital message which identifies them and gives their position,
as well as a signal that facilitates the final approach of the rescue teams.
They are suitable for all types of use (maritime, aeronautical and land) and can, depending on the model,
be activated manually or automatically. They are designed to function in the most extreme conditions with a
high degree of reliability.
(2)Satellites low earth orbiting:
At least four satellites are permanently operational. Since their orbit is near-polar, in the worst case every
point on Earth is overflown every two hours.
In a ground station's visibility zone, the satellites directly transmit the messages captured in that zone, and
also any messages from the zones not covered that they have stored in memory.
(3)Geo-stationary satellites are now available in the system and offer faster detection capability (close to 5
minutes) but require a GPS receiver to supply location that is sent via C/S message.
(4)Ground reception stations:
The zone effectively covered (or visibility zone) is a circle with a radius of 2,500 km around the station.
These stations receive (via the satellites) and process, in real time, the messages from the beacons
activated in their visibility zone and, in batch mode, the messages from the 406 MHz beacons activated
outside that zone and memorized by the satellites.
Automatic processing of the 406 MHz digital messages allows the beacons to be located and the carrier
mobile to be identified.