User's Manual

10
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87634_UM_TRON_40VDR_A
1.2.2 DISTRESS LOCATION DETERMINATION
The location of the distress signal is determined by taking
measurements of the doppler shift of the EPIRB frequency
when the satellite first approach and then pass the EPIRB.
The actual frequency is heard at the time of closest approach
(TCA). Knowing the position of the satellite and using the re-
ceived doppler signal information, it is possible to determine
the location of the Tron 40VDR from the satellite at the TCA.
At the LUT, actually two positions are calculated. One is the actual position (A)
and the other is the mirror image (B) position. A second satellite pass confirms
the correct location (A). Doppler-only accuracy is within 5 km (3 mi) (3.1 statute
miles or 2.6 nautical miles)— that is, the position is sufficiently accurate for SAR
purposes even after only one pass. What’s more, the most likely of the two ’mir-
ror’ positions can be determined valid with 98.5% accuracy after only one satel-
lite pass. This accuracy can be increased to 99.3% using so-called ”combined
Leo-Geo processing,” and this technique also enables accurate positions to be
generated with as little as two or three bursts from the beacon (i.e. less than 4
minutes of transmission) and thus greatly increases the chances of being found
even if the beacon is ultimately consumed by fire or is otherwise destroyed
1.2.3 GPS ADVANTAGE
Tron 40VDR has been designed to operate with the Cospas-Sarsat system and
will enhance further the lifesaving capabilities of conventional beacons.
Please see picture on next page for comparison between Tron 40VDR and
EPIRB without GPS depending on detection by polar orbiting or geostationary
satellites.
GPS position is updated every 6-16 minutes, and can also be tested in SELF-
TEST.