How Does It Work - mcmurdo Simrad EG50 Manual

How Does It Work?

11 HOW DOES IT WORK?
Your EPIRB contains two radio transmitters: one operating at 406 MHz
which transmits an alert which can be received by satellites, and one
operating at 121.5 MHz which transmits a signal which can be received
by overflying aircraft and Search & Rescue (SAR) homing receivers.
When you activate the EPIRB, both transmitters start broadcasting
signals. Providing the EPIRB's batteries are in good condition, the
transmission will continue for a minimum of 48 hours.
The 406 MHz alert signal can be detected by SAR satellites. American,
European and Indian authorities operate a series of satellites in low-
earth and geostationary orbits to detect and locate aviators, mariners
and land-based users in distress. The satellites, together with a world-
wide network of ground stations and Mission Control Centres (MCC)
form the International COSPAS-SARSAT Program whose mission is to
relay distress signals to the international search and rescue community.
These satellite systems are described in the Appendix.
Ground stations track these satellites and process the distress signals to
obtain a location (by using Doppler location techniques*) of the
distress. The processed information is then forwarded to an MCC
where it is combined with other location and registration information
and passed to a Rescue Coordination Centre (RCC) which alerts the
appropriate SAR authorities. Successive satellite passes refine and
confirm this information. Alternatively, beacons such as EG50 can use
the GPS system to obtain a very accurate position. This position is then
transmitted as part of the distress signal.
* For an explanation, visit the webpage:
http://www.cospas-sarsat.org/DescriptionOverview/doppler.htm
The network of orbiting satellites can detect signals over the entire
surface of the earth; in addition, there are four geostationary satellites
that appear fixed in position and which detect signals over enormous
areas (approximately one-third of the surface of the earth, but excluding
Polar regions). However, the geostationary satellites, because they are
fixed with respect to the earth, cannot determine the position of the
EPIRB using Doppler.
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