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406 MHz EPIRBs and PLBs: The safety device of choiceThe 406 MHz EPIRB was designed to operate with satellites. The signal frequency (406 MHz) has been designated internationally for use only for distress. Other communications and interference, such as on 121.5 MHz, is not allowed on this frequency. Its signal allows a satellite local user terminal to accurately locate the EPIRB (much more accurately -- 2 to 5 km vice 25 km -- than 121.5/243 MHz devices), and identify the vessel (the signal is encoded with the vessel's identity) anywhere in the world (there is no range limitation). These devices are detectable not only by COSPAS-SARSAT satellites which are polar orbiting, but also by geostationary GOES weather satellites. EPIRBs detected by the GEOSTAR system, consisting of GOES and other geostationary satellites, send rescue authorities an instant alert, but without location information unless the EPIRB is equipped with an integral GPS receiver. EPIRBs detected by COSPAS-SARSAT (e.g. TIROS N) satellites provide rescue authorities location of distress, but location and sometimes alerting may be delayed as much as an hour or two. These EPIRBs also include a 121.5 MHz homing signal, allowing aircraft and rescue craft to quickly find the vessel in distress. These are the only type of EPIRB which must be certified by Coast Guard approved independent laboratories before they can be sold in the United States. A new type of 406 MHz EPIRB, having an integral GPS navigation receiver, became available in 1998. This EPIRB will send accurate location as well as identification information to rescue authorities immediately upon activation through both geostationary (GEOSAR) and polar orbiting satellites. These types of EPIRBs are considered by many the best you can buy. Note that GEOSAR cannot detect 121.5 MHz alerts, nor can it route unregistered 406 MHz alerts to a rescue authority. GEOSAR cannot calculate the location of any alert it receives, unless the beacon has an integral GPS receiver. The major advantage of the 406 MHz low earth orbit system is the provision of global Earth coverage using a limited number of polar-orbiting satellites. Coverage is not continuous, however, and it may take up to a couple of hours for an EPIRB alert to be received. To overcome this limitation, COSPAS-SARSAT has 406 MHz EPIRB repeaters aboard three geostationary satellites, plus one spare: GOES-W, at 135 deg W; GOES-E, at 75 deg W; INSAT-2A, at 74 deg E; and INSAT-2B (in-orbit spare), at 93.5 deg E. Ground stations capable of receiving 406 MHz. Except for areas between the United Kingdom and Norway, south of the east coast of Australia, and the area surrounding the Sea of Okhotsk near Russia, as well as polar areas, GEOSAR provides continuous global coverage of distress alerts from 406 MHz EPIRBs. There is also a type of 406 MHz EPIRB that does not have integral GPS but has the capacity to integrate with onboard GPS systems. Some prefer this type of setup because it transmits location immediately upon activation if it was properly installed and hooked up to the GPS system. It does not require time to acquire and communicate with satellites. The drawback is that it will not update the position once it is deployed outside the vessel where the GPS connection was made. The Coast Guard recommends you purchase a 406 MHz EPIRB, preferably one with an integral GPS navigation receiver. A Cat I EPIRB should be purchased if it can be installed properly. The COSPAS SARSAT Organization estimates that the number of 406 MHz beacons in service at the beginning of 1998 was about 156,000. Most of these beacons are maritime EPIRBs. A note of caution. Once activated in an emergency situation, do not turn your EPIRB on and off to conserve batteries. This hampers acquisition of satellites and transmission of data. If you keep it on for the life of the battery, your chances of effective rescue are maximized. For a single voyage, you may consider the Boat US EPIRB rental program. It is a highly economical way to ensure the safety of your crew and your vessel when venturing beyond the coastal perimeter where VHF signals are likely to be received by SAR authorities.
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