User's Manual

5
3 PURPOSE
An Emergency Position Indicating Radio Beacon (EPIRB) is used to alert search and
rescue services in the event of an emergency. It does this by transmitting a coded
message on the 406MHz distress frequency. This message is relayed via satellite and
earth station to the nearest rescue co-ordination centre.
The satellite system is run by COSPAS-SARSAT, and has already been described.
With the geostationary satellite section being commissioned, the alerting delay is
reduced from typically 90 minutes to a few minutes within the geostationary satellite
coverage.
Instant alerting is good news, but they still need to know where you are. The
advantage of the G4 EPIRB is that it has a built in GPS receiver, so within minutes of
activation it will have determined your latitude / longitude coordinates and will have
transmitted these to the rescue centre. The position fix is accurate to 150m*.
To operate properly the G4 needs a clear view of the whole sky. If its view is blocked
and it is unable to get a position fix, then the system defaults to using a polar orbiting
satellite to determine position. In this case, there is typically a 45 minute delay before
the position is known and the accuracy is limited to within 5km (3 miles). This is the
original system that standard (non-GPS) EPIRBs use. To get the full advantage of the
G4 it is important to give it a clear view of the whole sky.
The G4 transmits a message that identifies the exact vessel to which it was registered.
Knowing which vessel is in distress allows the rescue services to eliminate false
alarms and launch an appropriate rescue.
The G4 also has a secondary distress transmitter. This transmits on 121.5MHz and is
used for “homing” purposes. When the rescue services get close, this allows them to
direction find on the signal. To cater for searches at night, the G4 has a bright flashing
light that aids final visual location.
S
E
A
L
READY
TEST
PRESS TO
Antenna
Strobe
Green lamp
Program point
Sea contacts
Lanyard
ON button
under here
READY
button
Battery expiry date
Red lamp
* If the programmed identity
is a Radio Call Sign (RCS)
then accuracy is limited to 5km