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VHF DSC is straightforward to use. 

Early models of VHF DSC radios were not known for their simplicity, however this situation has improved markedly, with a new technical standard which has eliminated many unnecessary functions and enhanced ease of use.

DSC is used as a means of establishing initial contact between stations.

Following an alert by DSC message, communications must be established  by radiotelephony on a different channel to that used for the DSC call.


VHF DSC channel 

VHF marine channel 70 is dedicated to DSC operation.  Radiotelephone calls are prohibited on Channel 70.


DSC call categories

The DSC system supports a number of call categories.  These categories mirror the standard maritime prioritisation of message traffic, ie:

DISTRESS

URGENCY

SAFETY

ROUTINE

Distress alerts are automatically addressed to all stations.

Urgency, safety and routine calls can be addressed to all stations, an individual station, or a group of stations.




Call formats

Every DSC call contains the following information:

  • the identity of the calling station;
  •  the priority of the call  - DISTRESS, URGENT, SAFETY or ROUTINE;
  • the station(s) being called (a specific station or ALL stations); and
  • the channel on which subsequent communications are to be carried out by radiotelephone  (apart from distress calls, which always default to channel 16). 



Maritime Mobile Service Identity (MMSI)

All stations fitted with DSC are allocated a unique 9 digit ID number, known as a Maritime Mobile Service Identity (MMSI).  

This MMSI is permanently programmed into the DSC equipment and is sent automatically with each transmission.

MMSI are allocated internationally, with the first 3 digits, known as the Maritime Identification Digits (MID), representing the station’s country of origin.  

The Australian MID is 503 and the New Zealand MID is 512.

When you apply for a MMSI, you supply the Search and Rescue (SAR) authorities with your details such as a physical description of your boat and contact details for your next of kin.

These details are entered into a database, so that if a DSC alert is received from your radio, the details are immediately available to SAR coordinators.

This significantly improves your chances of being rescued.

Obtaining an MMSI, operator qualifications and more operational info