Raymarine RAY91 - Digital Selective Calling (DSC)

6.1DigitalSelectiveCalling
(DSC)
TraditionalVHFradiosystemsrequireuserstolisten
untilsomeonespeaks,andthendeterminewhetherthe
callisforthem.DSCensuresthatcallsarereceivedby
alertingorannouncingtheintendedrecipient(s)firstso
theyarereadytolistentothesubsequentmessageon
therelevantchannel.
DSCispartoftheGlobalMaritimeDistressandSafety
System(GMDSS),amaritimecommunicationssystem
foremergencyanddistressmessagesandalltypes
ofroutinecommunicationssuchasship-to-shipor
ship-to-shore.
DSCisadigitalsignallingsystem,whichoperateson
VHFchannel70.DSCcallsincludeotherdatasuchas
yourvessel’sidentificationnumber,purposeofthecall,
yourpositionandthechannelyouwanttospeakon.
DSCcallscanbedividedinto4categoriesandare
prioritizedasshownbelow:
1.Distress
2.Urgency
3.Safety
4.Routine
Distress
ADistresscallshouldonlybeusedwhenthereis
imminentdangertoavehicleorpersonthatrequires
immediateassistance.
Whenmakingadistresscallthefollowinginformationis
transmittedtoallstationswithinrange:
•VesselMMSInumber.
•Vesselposition(mustbeinputmanuallyifnoGPS
positiondataisavailable).
•Localtime(mustbeinputmanuallyifnoGPSposition
dataisavailable).
•Natureofthedistress(whendesignated).
•Transmissionfrequency.
Thecallisautomaticallyrepeatedatapproximately4
minuteintervalsuntilitisacknowledgedeitherbya
coastradiostation(CRS)oravesselwithinradiorange.
DistresscallsmustbefollowedbyaMAYDAYcallon
prioritychannel16.
Urgency
Anurgencycallshouldbeusedwhenthereisdanger
toavehicleorpersonthatdoesnotrequireimmediate
assistance.
Whenmakinganurgencycallthefollowinginformation
istransmittedtoallstationswithinrange:
•VesselMMSInumber.
•Vesselposition(mustbeinputmanuallyifnoGPS
positiondataisavailable).
•Localtime(mustbeinputmanuallyifnoGPSposition
dataisavailable).
•Transmissionfrequency.
Onceanurgencycallissentitmustbefollowedwith
aPANPANvoicemessageonchannel16andinclude
thenecessarydetails.
Safety
Asafetycallshouldbeusedwhenthereisan
importantnavigationalwarningormeteorological
forecast/broadcast.Safetyalertscanalsousedfor
communicationsduringsearchandrescueoperations.
Whenmakingasafetycallthefollowinginformationis
transmittedtoallstationswithinrange:
•VesselMMSInumber.
•Vesselposition(mustbeinputmanuallyifnoGPS
positiondataisavailable).
•Localtime(mustbeinputmanuallyifnoGPSposition
dataisavailable).
•Transmissionfrequency.
Onceasafetycallissentitmustbefollowedwitha
SECURITEvoicemessageonchannel16andinclude
thenecessarydetails.
Routinecalls
Routinecallsareusedforcontactingothervessels,
marinas,orshorestations.
Routinecallsaremadeonchannel70usingthe
dedicatedMaritimeMobileServiceIdentity(MMSI)
numberofthestationtobecontacted,selectinga
VHFworkingchannelandsendingthecall.Both
radiosautomaticallyswitchtothechosenchannelfor
conversation.
Routinecallscanalsobemadetogroups—When
groupsofshipsneedthesameinformation(yachtraces,
clubralliesetc.)aspecialgroup-callidentitycanbeused
toenablerestrictedbroadcastcalls.
Note:T otransmitprecisepositions,theradiomust
beinterfacedtoaGPSreceiver.Otherwise,regular
manualpositionupdatingisrequired.
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