ELECTRONICS
position immediately, without having to wait for an
internal GPS to determine a position from a “cold start.”
In ideal conditions with a good view of the sky, the
integrated GPS might take only two to three minutes
or less to determine a position from a cold start, but in
large seas with water periodically dousing the beacon,
it could be closer to five or 10 minutes before a location
is ascertained. However, once the internal GPS has
acquired a position, the EPIRB will be updated with a
new reading every 20 minutes, and this has the potential
to provide rescuers with a quasi-real-time position that
takes into account any drift that may have occurred
after the beacon was initially activated.
A nice feature to have in an EPIRB with GPS
capability is an LED or other visual indicator that tells
whether the GPS receiver has acquired a valid position.
In situations where the view of the sky is limited and
the GPS receiver cannot acquire a position, GEOSAR
satellites frequently are able to determine the location,
although it may take several passes to do so. One of the
strengths of determining position by GEOSAR is the
fact the satellites are moving across the sky, so a location
that’s blocked by obstructions on one or more sides can
still be seen by the satellite as it passes overhead.
THE PERSONAL LOCATOR BEACON, OR PLB
In July 2003, a new device called the Personal Locator
Beacon (PLB) was approved for use in the United States.
The PLB is fully compatible with the COSPAS-SARSAT
system, and, as with EPIRBs, the owner is required to
register the beacon with the NOAA. Versions are available
with external GPS connections or internal GPS receivers
to provide position information to the beacon transmitter.
PLBs are noticeably smaller than marine EPIRBs; even the
largest will fit comfortably into a good size pocket. There
are a few differences in their design specifications and
operation, most of them generated by the desire for
smaller, more portable devices. To begin with, all PLBs
must be manually activated. There is no provision for
the PLB to automatically activate when it is immersed in
water or by any other means. Unlike full-size EPIRBs,
which must be capable of transmitting for 48 hours after
activation, PLBs are required to operate for only 24 hours.
As with EPIRBs, there are Class 1 and Class 2 batteries,
