Digital Selective Calling has become an integral part of marine VHF Communication. Here we give an overview of how it works, what is does and the issues that affect you
Digital Selective Calling (DSC) is primarily used to initiate distress calls to shore stations and other vessels via your DSC radio and provides recipients of your emergency call with:
– Your Vessel’s Identity
– Your Precise Position (if interfaced with GPS)
– Your Unique MMSI Number (Maritime Mobile Service Identity)
– The Nature of your Distress
All DSC-equipped shore stations and vessels will hear your distress signal as an alarm. It will be repeated every 4 minutes until acknowledged. A DSC alert signal has a 15% greater range than a voice transmission and therefore is more likely to reach a vessel or rescue centre.
In a potentially dangerous situation, a DSC alert signal is the quickest way to initiate emergency communications with ships and rescue coordination centres. DSC saves vital time by allowing you to speak to the emergency authorities and plan your next move.
If integrated with GPS navigational equipment (highly recommended), a vessel’s position and time of transmission are automatically included in the DSC distress and urgency alerts, an important point when you find yourself in trouble. If your DSC is not linked to a GPS, manual input of your coordinates is required. When linked to a GPS, it is simply a case of pressing the red DSC button to summon help.
It is critical that your DSC radio is properly installed and that you are licensed to use it. Without these two things you will not benefit from DSC. MMSI’s are important in the UK as they are assigned as part of the ship’s radio licensing procedure. Without a MMSI programmed radio, you cannot access full DSC functions. With the wrong MMSI number entered, you will be using the radio illegally and putting your life at risk.
Make sure you are licensed…
You will need two licences; one for the vessels radio and another for the operator.
The vessel’s licence is the key to obtaining an MMSI number, which will uniquely identify your vessel to the Coastguard, just like a car registration number. You can obtain an application form for a vessel radio license from OFCOM.
You will also require an operator’s licence and will have to pass the Short Range Certificate (SRC) which is taught at most sailing schools and adult education centres. The SRC course is straightforward and covers VHF and DSC radio etiquette and procedures. This usually takes a day to complete.
It is no longer mandatory for rescue services to maintain ‘listening watch’ on VHF Channel 16.
All large vessels and almost all Coastguards over Europe are fully-equipped for DSC and will respond instantly. GMDSS is an automatic, worldwide system and can be used anywhere, avoiding possible language barriers.
If you are in trouble, DSC allows you to call every other radio in range, simultaneously.
You can contact vessels via their MMSI number – choose the channel you wish to use, then ask your radio to call them by choosing their name from a menu or input their MMSI number. If they are in range, their DSC radio will sound an alarm tone (like a telephone) and once they acknowledge your call, both radios will automatically switch to your chosen channel.