Digital Selective Calling (Dsc) - Raymarine Ray260 User Manual

7.1 Digital Selective Calling (DSC)

Traditional VHF radio systems require users to listen until
someone speaks, and then determine whether the call is for
them. DSC ensures that calls are received by alerting or
announcing the intended recipient(s) first so they are ready to
listen to the subsequent message on the relevant channel.
DSC is part of the Global Maritime Distress and Safety System
(GMDSS), a maritime communications system for emergency
and distress messages and all types of routine communications
such as ship-to-ship or ship-to-shore.
DSC is a digital signalling system, which operates on VHF
channel 70. DSC calls include other data such as your vessel's
identification number, purpose of the call, your position and the
channel you want to speak on.
DSC calls can be divided into 4 categories and are prioritized
as shown below:
1. Distress
2. Urgency
3. Safety
4. Routine
Distress
A Distress call should only be used when there is imminent
danger to a vehicle or person that requires immediate assistance.
When making a distress call the following information is
transmitted to all stations within range:
• Vessel MMSI number.
• Vessel position (must be input manually if no GPS position
data is available).
• Local time (must be input manually if no GPS position data
is available).
• Nature of the distress (when designated).
• Transmission frequency.
The call is automatically repeated at approximately 4 minute
intervals until it is acknowledged either by a coast radio station
(CRS) or a vessel within radio range. Distress calls must be
followed by a MAYDAY call on priority channel 16.
Urgency
An urgency call should be used when there is danger to a vehicle
or person that does not require immediate assistance.
When making an urgency call the following information is
transmitted to all stations within range:
• Vessel MMSI number.
• Vessel position (must be input manually if no GPS position
data is available).
• Local time (must be input manually if no GPS position data
is available).
• Transmission frequency.
Once an urgency call is sent it must be followed with a PAN PAN
voice message on channel 16 and include the necessary details.
Safety
A safety call should be used when there is an important
navigational warning or meteorological forecast/broadcast.
Safety alerts can also used for communications during search
and rescue operations.
When making a safety call the following information is
transmitted to all stations within range:
• Vessel MMSI number.
• Vessel position (must be input manually if no GPS position
data is available).
• Local time (must be input manually if no GPS position data
is available).
• Transmission frequency.
Once a safety call is sent it must be followed with a SECURITE
voice message on channel 16 and include the necessary details.
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Routine calls
Routine calls are used for contacting other vessels, marinas,
or shore stations.
Routine calls are made on channel 70 using the dedicated
Maritime Mobile Service Identity (MMSI) number of the station
to be contacted, selecting a VHF working channel and sending
the call. Both radios automatically switch to the chosen channel
for conversation.
Routine calls can also be made to groups — When groups of
ships need the same information (yacht races, club rallies etc.)
a special group-call identity can be used to enable restricted
broadcast calls.
Note: To transmit precise positions, the radio must be
interfaced to a GPS receiver. Otherwise, regular manual
position updating is required.
Ray260