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vessels, can send distress, all ships urgency, all ships safety and individual alerts/announcements on VHF channels on DSC channel 70. On both class A and D you can be directed to Ch 06, 08, 72, 77 or other simplex channel for the follow-up RT (radio telephony ) call. Class D has only one antenna and thus can only watch
Channel 70 when not transmitting. For routine alerts, which are used to establish communication with another station on a working channel, the receiver acknowledges to confirm that communication can be done on the appropriate channel.
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162:". To avoid false distress alerts, distress buttons normally have protective covers, often with a spring-loaded cover so two hands need to be used simultaneously. Alternatively, some devices have two-button systems. Operators are required to cancel falsely sent distress alerts with a transmission on the channel designated by the distress signal.
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A coast station which receives a DSC distress alert will wait 2.75 minutes prior to sending an acknowledgment to allow other vessels in the nearby area to receive the alert. This helps shore stations narrow down where a vessel without GPS is located. The sending device will then both stop repeating
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transmissions in the 2, 4, 6, 8, 12 and 16 MHz marine bands. At minimum, controllers will monitor 2187.5 kHz and 8414.5 kHz and one more band. However for automated monitoring a second, receive-only antenna is often needed (especially on non-commercial leisure boats) since a separate
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for each sending, without waiting for an acknowledgment, a multi-frequency attempt should only be done if there are only a few minutes until the ship's batteries are under water. As the distress message can only be sent on one of the bands, many ships and coast stations may be listening to a band
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Class A VHFs, used on commercial ships, have the ability to send distress, distress relay, all ships urgency, all ships safety, individual, group, geographic area and telephone alerts/announcements on DSC channel 70 (Digital channel reserved for DSC only.). Class D VHFs, used for most leisure
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the alert, and tune to the designated channel for the distress message to be sent. Ships receiving a distress alert who are outside coast station range or do not receive an acknowledgment, are required to relay the distress alert by any means to land.
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messages. The distress can be sent either as a single-frequency or multi-frequency attempt. In the former, a distress signal is sent on one band and the system will wait up to four minutes for a DSC acknowledgment from a
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Distress calls can be both non designated and designated. The latter allows one of ten predefined designations to be sent along with the distress signal. These are "abandoning ship", "fire or explosion", "flooding",
141:. If none is received, it will repeat the distress alert up to five times. In a multi-frequency attempt, the distress signal is sent on the MF and all the HF distress frequencies in turn. As this requires
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The priorities for communication are, Distress, Urgency, Safety and
Routine. A Distress DSC call is called an Alert. Urgency, Safety and Routine are called Announcements.
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There is a general consensus for routine calls to use 2177.0, 4208.0, 6312.5, 8415.0, 12577.5, and 16805.0 kHz (the first frequency listed above in each band).
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tuner is used apart from the main one; this is separate from programming radios to monitor user-defined DSC frequencies (which would use the main antenna).
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DSC was developed to replace a voice call in older procedures. Because a DSC signal uses a stable signal with a narrow bandwidth and the receiver has no
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control panel showing a (simulated) distress message. This unit made by ICS controls DSC messaging for VHF, MF and HF transceivers
424:"Recommendation M.541: Operational procedures for the use of digital selective-calling equipment in the maritime mobile service"
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233:. For High Frequency and Medium Frequency two tones 170 Hz apart either side of the allocated frequency with 100
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241:. Each character is transmitted twice with a time delay. The detailed specification is published in the
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symbol rate are used. For VHF the two tones used are 1300 and 2100 Hz with a symbol rate of 1200
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86:(GPS), which allows the apparatus to know who it is, what time it is and where it is. This allows a
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Often, ships use separate VHF DSC and MF/HF DSC controllers. For VHF, DSC has its own dedicated
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without the message, and will after five minutes relay the distress signal to a coast station.
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460:"M.493 : Digital selective-calling system for use in the maritime mobile service"
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158:", "grounding", "listing", "sinking", "disabled and adrift", "piracy or attack" and "
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if radio is connected to GPS system and, if necessary, the channel for the following
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When sending a distress signal, the DSC device will at minimum include the ship's
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recommendation ITU-R M.493, revision 15 published in 2019 being the most recent.
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The DSC is a synchronous system using characters composed from a ten-bit
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for monitoring
Channel 70, but uses the main VHF transceiver for
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442:"Routine HF-DSC Frequencies/Icom M-802 "DSC Watch Mode" Freqs"
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46:(VHF) maritime radio systems. It is a core part of the
486:(Fourth ed.). London: Adlard Coles Nautical.
342:"HF/SSB DSC Routine Calling with Icom M801E/M802"
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299:"General Coverage / WeatherFAX / DSC Antenna"
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82:(MMSI) and may be connected to the ship's
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181:While there are reserved frequencies for
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532:International telecommunications
213:25208.5, 25209, 25209.5 kHz
210:22374.5, 22375, 22375.5 kHz
207:18898.5, 18899, 18899.5 kHz
201:12577.5, 12578, 12578.5 kHz
124:number. It may also include the
80:Maritime Mobile Service Identity
507:. Dobbs Ferry: Sheridan House.
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364:"DSC Global NavArea Group IDs"
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229:. The bits are encoded using
204:16805, 16805.5, 16806 kHz
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362:Reynolds, Mike (2016-04-17).
340:Reynolds, Mike (2015-06-10).
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195:6312.5, 6313, 6313.5 kHz
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542:Telecommunication protocols
198:8415, 8415.5, 8416 kHz
192:4208, 4208.5, 4209 kHz
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90:to be sent very quickly.
84:Global Positioning System
28:Digital selective calling
480:Bréhaut, Denise (2009).
320:"ICOM M802 DSC antenna?"
501:Payne, John c. (2006).
537:Maritime communication
368:Yacht Zen Again Weblog
346:Yacht Zen Again Weblog
231:frequency-shift keying
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24:
483:GMDSS: A User's Guide
189:2177, 2189.5 kHz
183:distress HF DSC calls
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23:A Sailor VHF DSC unit
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16:Marine radio standard
301:. Metz Communication
227:error detecting code
44:very-high-frequency
504:Boat Communication
413:Bréhaut (2009): 43
404:Bréhaut (2009): 44
395:Bréhaut (2009): 40
383:Bréhaut (2009): 38
288:Bréhaut (2009): 37
267:Bréhaut (2009): 35
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493:978-1-4081-1493-3
221:Technical details
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99:transmission
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59:touch screen
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126:coordinates
105:and safety
526:Categories
305:2016-05-17
249:References
134:radiotelex
156:collision
50:(GMDSS).
42:(HF) and
143:retuning
116:Distress
108:sécurité
95:receiver
66:Workings
466:. 2019.
430:. 2015.
147:antenna
103:urgency
72:squelch
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57:A DSC
38:(MF),
509:ISBN
488:ISBN
239:Baud
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145:the
122:MMSI
132:or
32:DSC
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