Beacon modes Emergency position-indicating radiobeacon station
1 beacon modes
1.1 digital mode: 406 mhz beacons
1.1.1 406 mhz beacon facts , transmission schedule
1.1.2 hex codes
1.2 ais sart
1.3 analog mode: other beacons
beacon modes
the important aspect of beacon in classification mode of transmission. there 2 valid transmission modes: digital , analog. digital has longer range, analog more reliable. analog beacons useful search parties , sar aircraft, though no longer monitored satellite.
digital mode: 406 mhz beacons
406 mhz beacons transmit bursts of digital information orbiting satellites, , may contain small integrated analog (121.5 mhz) homing beacon. can uniquely identified (via geosar). advanced beacons encode gps or glonass position signal. beacons located doppler triangulation confirm location. digital data identifies registered user. phone call authorities registered phone number eliminates false alarms (false alarms typical case). if there problem, beacon location data guides search , rescue efforts. no beacon ignored. anonymous beacons confirmed 2 doppler tracks before beginning beacon location efforts.
the distress message transmitted 406 beacon contains information such as:
which country beacon originates from.
a unique 15-digit hexadecimal beacon identification code (a 15-hex id ).
the encoded identification of vessel or aircraft in distress, either mmsi value, or as, in case of elt, either aircraft s registration or icao 24-bit address (from mode-s transponder).
when equipped, gps position.
whether or not beacon contains 121.5 mhz homing transmitter.
the digital distress message generated beacon varies according above factors , encoded in 30 hexadecimal characters. unique 15-character digital identity (the 15-hex id) hard-coded in firmware of beacon. 406.025 mhz carrier signal modulated plus or minus 1.1 radians data encoded using manchester encoding, ensures net 0 phase shift aiding doppler location
406 mhz beacon facts , transmission schedule
406 mhz beacons transmit quarter of second when turned on, , transmit digital burst once every 50 seconds thereafter. both geosar , leosar satellites monitor these signals.
the repetition period shall not stable 2 transmitters appear synchronized closer few seconds on 5-minute period. intent no 2 beacons have of bursts coincident. period shall randomised around mean value of 50 seconds, time intervals between transmission randomly distributed on interval 47.5 52.5 seconds. (specification first-generation beacons)
preliminary specification second-generation beacons. beacon activation total of [6] initial transmissions shall made separated fixed [5s ± 0.1s] intervals. first transmission shall commence within [3] seconds of beacon activation. transmissions shall occur @ nominally [30] second intervals until [30 ± 1] minutes after beacon activation. repetition period between start of 2 successive transmissions shall randomised around stated nominal value, intervals between successive transmissions randomly distributed on ± [5] seconds. subsequent transmissions [tbd].
406 mhz beacons beacons compatible meosar (dass) system.
406 mhz beacons must registered (see below).
hex codes
example hex codes following: 90127b92922bc022ff103504422535
a bit telling whether message short (15 hex digits) or long (30 hex digits) format.
a country code, lets worldwide cospas/sarsat central authority identify national authority responsible beacon.
embedded 15-hex id or 15-hex transmitted distress message, example, 2024f72524ffbff hex id printed or stamped on outside of beacon , hard-coded firmware. 15-hex id can reprogrammed certified distress radiobeacon technicians. national authority uses number phone numbers , other contact information beacon. crucial handle large number of false alarms generated beacons.
a location protocol number, , type of location protocol: epirb or mmsi, data fields of location protocol. if beacon equipped gps or glonass, rough (rounded) latitude , longitude giving beacon s current position. in aircraft beacons, data taken aircraft s navigation system.
when beacon sold country, purchaser responsible having beacon reprogrammed new country code , register his/her nation s beacon registry, , seller responsible de-register deprecated beacon id his/her national beacon registry.
one can use beacon decoder web page @ cospas-sarsat extract 15-hex id 30-hex distress message.
ais sart
these devices distinct traditional sar radar transponders (sart), transmit ais messages containing accurate gps position information , include gps receiver , transmitter on vhf ais channels, show on ship ais receivers. lightweight , can used equip inflatable liferafts.
analog mode: other beacons
a simple analog siren tone transmitted continuously until battery dies.
in case of 121.5 mhz beacons, frequency known in aviation vhf guard emergency frequency, , u.s. civilian pilots (private , commercial) required, faa policy, monitor frequency when possible so. frequency can used automatic direction finder (adf) radionavigation equipment, being phased out in favor of vor , gps still found on many aircraft.
the cospas-sarsat system detected type of beacon – prior 1 february 2009 – when leosar satellite in view of both beacon , leolut (ground segment). satellite detection of 121.5 mhz beacons ceased on 1 february 2009 (see below).
^ albert helfrick, principles of avionics, 5th edition, avionics communications, 2009 isbn 1885544278, p 287
^ http://www.cospas-sarsat.int/images/stories/systemdocs/current/cs-t-001-oct2014.pdf
^ http://www.cospas-sarsat.int/images/stories/systemdocs/current/t-018-oct-2014.pdf
^ nasa search , rescue mission office : distress alerting satellite system (dass) archived 2016-03-04 @ wayback machine.
^ example of 406 mhz beacon coding
^ beacon decoder webpage archived 2012-03-09 @ wayback machine., when 1 enters transmitted (i.e. gps-location-included) 15-hex decoder, unmodified 15-hex id printed @ bottom of output of beacon decoder page. method can used confirm beacon encoding correct 15-hex id (as printed on side of beacon) distress messages. accessed november 23, 2009
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