This article appears courtesy of the US Coast Guard. USCG Officer Jim Krezenski, the author, wrote it as a primer on the use of EPIRBs.
An EPIRB, or Emergency Positioning Indicating Radio Beacon is a small battery-powered transmitting device that is carried on board, used only in case of emergency, and usually only as a last resort when your marine radio is inoperable or you are out of range. At last count, 11,471 persons have been rescued using the network of satellites these devices rely upon. Who knows, you could be next.
There are several types of EPIRBs, and the specifics vary from model to model. If a disaster strikes, some float free and automatically activate; others must be activated manually. All EPIRBs float and will send out a continual signal for 48 hours. Since EPIRB signals are primarily detected by a network of international satellites that pass overhead, occasionally there may be a delay in detection, perhaps up to an hour, because there is no satellite currently in the area to pick up the signal and relay it to shore-side rescue bases.
121.5 MHz Class B EPIRBs that operate on 121.5/243 MHz are the least expensive, and the least capable. These were designed in the 1970s to alert aircraft flying overhead. This type of EPIRB is not well suited for satellite detection because of the problem of distinguishing them from other signals on the same frequency. Often, multiple passes of the satellites are required to identify the signal, which can further delay the rescue. And these frequencies are not stored by the satellites, therefore it is possible to find yourself in "dead zones" where no one may hear the signal. This effectively limits the 121.5 MHz EPIRBs to coastal use. These units also have a finite lifespanthe 121.5 MHz EPIRB is due to be phased out February in 2009.
All 121.5 MHz EPIRBs, often referred to as category B or mini Bs, are manual-activation units. Although these units do work with the low-earth orbiting satellite system, they do not work as well as 406 MHz beacons, and they can not be detected by the geostationary satellites that provide instantaneous alerting for 85 percent of the globe. Furthermore, 121.5 MHz beacons account for a large amount of the wasted efforts by search and rescue forces. Most 406 MHz false alerts can be resolved easily with a phone call, and in contrast, every 121.5 MHz false alert must be tracked to the source using direction-finding equipmenta costly waste of resources for already over-taxed search and rescue organizations.
|"It's very important that you mount Category I EPIRBs outside the cabin where they will be able to float free of the sinking vessel."|
For offshore sailors, the 406 EPIRBS are the only common sense choice. The major advantage of the 406 MHz low-earth-orbit system is the provision of global coverage using a limited number of polar-orbiting satellite. Coverage is not continuous, however, and it again may take up to a couple of hours for an EPIRB alert to be received.
While the 406 Mhz signal frequency has been designated internationally for use only for distress, these units also include a 121.5 Mhz signal that is used mainly for homing. The signal emitted is capable of being picked up by aircraft, which may be 100 miles or more away, and by satellites orbiting more than 500 miles above the earth. While these units are more expensive, imagine yourself floating in a liferaft in the middle of the ocean, and the issue of price will likely become moot. Response time to the 406 EPIRB is dramatically reduced and the position information it provides is much more accurate.
The good frequency stability of the 406 MHz EPIRB's signal leads to a doppler estimation of the EPIRB's position between one and 50 miles. Satellites store the EPIRB's position and transmit that information when it flies over a satellite reciever. This eliminates dead zones giving the 406 MHz EPIRB global coverage.
406 EPIRBs are carried on all US-flagged merchant vessels and are also required on commercial fishing vessels operating beyond three miles from shore. EPIRBs are also required to be licensed by the Federal Communications Commission. They should be listed on your ship's station license. Although EPIRBs are not required on recreational vessels, the USCG strongly recommends them and strongly suggests that the choice be the Category I, 406 MHz model. Its long-reaching, long-lasting signal can make a significant difference in the speed and effectiveness of rescue efforts.
In a recent test of the 406 MHz model, a Naval Academy midshipman found out how effective it was. The test signal was identified within four minutes and pinpointed within 15 minutes. If that is not enough to convince you, the comparison chart below may help you make up your mind whether or not you want to "bet your life" to save a little money.
Category I, 406 MHz model
Category II, 121.5/243 MHz model
Global detection - Regional satellite
Regional earth station needed - not
Reliable beacon with low false alarms
Beacons often incompatible with satellites.
Beacon signal coding and exclusive
High false alert rate due to alerts
1.5 nautical mile accuracy and a
10-20 nautical miles accuracy. Search
Beacon is coded with owners name,
No way to know whether signal is from
Good ambiguity resolution, i.e. can
Hard to know which of two separate
Putting it to the TestA EPIRB needs periodic testing to ensure that the unit will work when called upon. Most units have a test option, but the tester should be aware that this tests the entire systemand can be the source of false alarms that can be easily prevented. The test switch activates a microprocessor on board that fires up the transmitter, oscillator, formulates a test signal, sets off the strobe light and finally broadcasts a live test transmission.
The microprocessor checks to see that all the operational elements test positive and then it gives confirming beeps and flashes. The microprocessor will not give off the appropriate confirming beep or flash if any element fails to perform and the user should take the beacon to an authorized service station for evaluation.
Operational transmission testing of a Class A or B EPIRB may only be legally executed during the first five minutes of every hour and only for three tone or one operational transmission second. During the first five minutes of every hour you can verify that your EPIRB is actually transmitting by turning it "on" near an FM radio tuned to 99.5 MHz. Placing the EPIRB a few inches from the FM radio will allow it to receive the signal and broadcast the familiar "warble" through its speakers if the EPIRB is transmitting properly. Conduct this test only during the first five minutes of each hour as indicated above.
All the lifesaving gadgets in the world won't help if they aren't properly maintained. Proper registration of your 406 MHz satellite emergency position-indicating radio beacon (EPIRB) is intended to save your life, and is mandated by Federal Communications Commission regulations. The Coast Guard is enforcing this FCC registration rule. If the EPIRB is properly registered, the Coast Guard will be able to use the registration information to immediately begin action on the case. If the EPIRB is unregistered, a distress alert may take as much as two hours longer to reach the Coast Guard over the international satellite system. If an unregistered EPIRB transmission is abbreviated for any reason, the satellite will be unable to determine the EPIRB's location, and the Coast Guard will be unable to respond to the distress alert. Unregistered EPIRBs have needlessly cost the lives of several mariners since the satellite system became operational. It's also easy. Registration can be mailed, or faxed in. For an online form, click here http://www.sarsat.noaa.gov/
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