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Press Release
Finding Emergency Beacons

Price, UT - August 2009 -- Some activities like flying and boating bring with them legal requirements to carry Emergency radio beacons. In past years emergency beacons transmitted on 121.5 MHz and or 243.0 MHz. February 1st of this year saw an end of satellite detection of the legacy radio frequencies. The COSPAS-SARSAT system no longer listens for them.


Emergency Locator Beacons (ELT), Emergency Position Indication Radio beacon (EPIRB) and Personal Locator Beacons are all basically the same. The big difference is their method of activation and who uses them. ELTs are activated by a shock and used by aircraft. EPIRBs are designed for maritime use and PLBs can be used (in the United States) by anyone in distress.


Although 121.5 MHz and 243.0 MHz are not longer monitored by satellites, the frequencies have not gone away. Even new emergency beacons can have 121.5 MHz homing beacons built in. Most do. The output power of the homing beacon has been turned down; consequently, Search and Rescue personnel need to be closer to a beacon to detect it on 121.5 MHz than they would have been in pre-406 MHz beacon days.


To compensate for the lower 121.5 MHz output power, 406 MHz beacons transmit a 5 watt pulse which is considerably higher than even the old 121.5 MHz emergency beacons. To achieve adequate battery life the 406 MHz signal is only transmitted approximately every 50 seconds. The transmit time is intentionally random to insure that if two beacons are activated at the same time they will never be synchronized and transmit at the same time all the time. It is still possible that they will have random events when they both transmit concurrently.


Some emergency beacons include built in GPS receivers or a port to receive GPS data from an external GPS. This is to feed a GPS location to COSPAS-SARSAT. This is great when it works. Remember we are not in a perfect world. Aircraft like to flip over and cover the GPS antenna. I have seen PLBs and EPIRBS put in the cabin of boats for protection by the crew or the boat capsize either of which will effectively block the GPS antenna. I have even seen PLBs placed face down in the snow blocking the GPS signal.


COSPAS-SARSAT is a great system and has taken into account some of the problems of the real world and the GPS weaknesses. Even if the beacon doesn’t have GPS data for any reason the beacon is still transmitting a radio beacon approximately once every 50 seconds and the 121.5 MHz homer is constantly transmitting. COSPAS-SARSAT can triangulate a beacon from the 406 MHz pulses and give an approximate location of the beacon.


After an approximate location is determined a radio direction finder like the RHOTHETA RT-600 / DF-517 is capable of detecting and tracking the beacon. Even the short pulse of the 406 MHz burst can be tracked.


The RT-600 / DF-517 can scan and detect all 19 COSPOS-SARSAT 406 MHz frequencies, decode the data it is transmitting and display it for SAR teams.


Depending on terrain and altitude of the RT-600 detection and tracking of the signal is possible from 90 nautical mile or greater. As you get closer to the beacon the direction finder can be tuned to 121.5 MHz to track the continues signal making it possible to locate a beacon in any weather or lighting condition.


The RT-600 / DF-517 has frequency agility giving the operator the ability to track a number of radio sources. In addition to emergency beacons law enforcement agencies track other beacons like LoJacks theft recovery system and Electronic Tracking Systems beacons.


Although we aviation types like to fly, weather and other factors must be considered. In addition to aviation radio direction finder RHOTHERTA also manufactures equipment for maritime and land use.


In a perfect world emergency beacons would not be needed; however, we are not there. Aircraft go down, boats sink and people get lost in the woods. Other bad things happen to good people. An emergency beacon can save your life.


Lon B. Arnold is the President of RHOTHETA USA, Inc. He has been involved with airborne and ground emergency services for the past 30 years. He can be reached at lon.arnold@rhothetaamerica or by phone at 435-578-1270.

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