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Chuck Husick: Techno-Talk, May 2003 BoatUS Magazine - Updated August 2009

Personal Locator Beacons (PLB's)


In the 27 years since COSPAS–SARSAT was launched in 1982 the system has been instrumental in saving more than 25,000 lives world-wide. The system continues to be improved, with new SARSAT equipment being included in the payloads of satellites such as the U.S. NOAA-N launched earlier this year.

Regarding the original SARSAT signaling devices, the 121.5 MHz transmission from first generation Emergency Locator Transmitters (ELTs) and EPIRBs are no longer monitored by the satellite constellations and should not be relied upon as an effective means for contacting the SAR authorities. The 406 MHz EPIRB and the similar, smaller, lighter and generally less costly PLB are the preferred means for informing the outside world of your need for assistance.

The typical PLB is small enough to fit in a pocket (about two-by-three-by-six inches) and light enough (just over a pound) to be carried or worn without difficulty. All are waterproof, some will float. Like the 406 EPIRB, a PLB transmits simultaneously on both 406 MHz (to alert the listening satellites) and on 121.5 MHz to provide a homing signal for searching aircraft and ground parties. While the transmit power on 406 MHz PLBs is the same as the larger marine EPIRBs (five watts), the specified transmit time is 24 hours, half that of the EPIRB. Battery life is typically the same as that specified for the EPIRB, five years. The new types of inherently safe batteries used in some of the PLBs allow them to be shipped without the restrictions necessary when Lithium primary cell batteries are used (common in EPIRBs where significantly longer operating life requires the use of batteries that have the greatest energy storage capacity).

Each PLB’s transmission includes a unique identification number, therefore the buyer is required to register the unit with the SAR authorities. The simple one-page form can be downloaded from www.sarsat.noaa.gov. As with EPIRBs, PLB re-registration will be required every two years. Some PLBs provide an interface connection to an external GPS receiver, others have internal GPS receivers (position information is not displayed, it is only available for transmission as part of the mayday call).


The signals sent by EPIRBs and PLBs are monitored by both the COSPASS–SARSAT polar orbiting satellites and geostationary satellites. After a beacon is activated, about 20 minutes is needed for the data collection and processing required to determine the beacon’s location with an accuracy of about three miles. The appropriate rescue center is then alerted. A satellite that receives a beacon signal containing position information will immediately relay the information to the ground data processing system, alerting a rescue center in as little as three to five minutes, with position information accurate to about 100 feet.

Rescue center responsibility for an EPIRB or PLB call is assigned based on the location of the mayday. PLBs are likely to be carried by people hiking, boating or canoeing in remote areas. While the Coast Guard will continue to deal with all marine locations, signals originating inland will be handled by the SAR component of the National Park Service of the Department of the Interior.

Should you purchase a new PLB it’s important to learn the proper way to test your beacon. While the “old” style 121.5/243.0 MHz beacons could be tested by turning them on for one second during the first 5 minutes of every hour, this type of live transmission test is prohibited with the 406 MHz beacons. Although the precise test method varies among manufacturers, most 406 units contain a microprocessor that will check for normal function and announce the result by emitting a confirming beep and or flash of its LED or strobe light. Check the instructions that came with your beacon and be sure you follow them precisely. The SAR folks have enough to do without responding to an inadvertent mayday call.

Also, know the battery replacement date. While replacement batteries are not cheap, your life should be worth the cost of a proper replacement battery. While some types of batteries can be replaced by the owner of the beacon, many manufacturers either require or strongly suggest that the unit be returned to the factory or sent to an authorized service facility for battery replacement, inspection and performance testing. It's worth remembering that the money you spent buying and maintaining beacon may be the best investment you ever made. Be sure the activating switch is in the “off and locked” position before you send it off for battery replacement. The SAR folks don’t want to have to come to the aid of a postal delivery truck on the Interstate.





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