Digital selective calling (DSC) was developed to replace a call in older procedures. Because a DSC signal uses a stable signal with a narrow bandwidth and the receiver has no squelch, it has a slightly longer range than analog signals, with up to 25 percent longer range and significantly faster. DSC senders are programmed with the ship’s Maritime Mobile Service Identity (MMSI) and may be connected to the ship’s Global Positioning System (GPS), which allows the apparatus to know who it is, what time it is and where it is. This allows a distress signal to be sent very quickly.

There are major advantages in Digital Selective Calling (DSC).

How does it work?

DSC compliant radios are easily recognizable by a distinctive red button marked “Distress“. Satellite and digital technology used for several years on commercial ships is now available to the recreational boater. DSC radios allow boaters to make ship-to-ship private calls and the DSC distress channel is currently being monitored by commercial ships and some coastal guard stations.

To participate in the digital messaging, your radio must be registered to get a 9 digit identity called Maritime Mobile Service Identity (MMSI).  In South Africa, you will get your MMSI number from ICASA. This becomes, much like a cell phone, your boat’s unique phone number.

In an Emergency

When pressing the emergency button your VHF will send out a general emergency call including details of your MMSI number and your exact position – all automatically! Even if everyone on board becomes incapacitated, the VHF will continue to broadcast the emergency with all relevant details.

Commercial ships and coastguard stations (where installed) monitor these broadcasts. Commercial ships will relay maydays to the Coast Guard where coastal monitoring is not installed yet. Because your MMSI number is unique, the Coast Guard has all the details of your boat, so it knows who you are, exactly where you are, and that you are in trouble.

What else can DSC do?

Another feature of the DSC radio is the ability to place private ship-to-ship calls to other vessels equipped with DSC radio. Basically if you know the MMSI number of the radio you are calling only that vessel will receive you message. Just like using your cell phone.

How many times have you tried to contact a friend, who you know is on the water, on the radio? Tried him on 16 – no response. See if he’s listening on 9 – no response. Frustrating!

DSC solves all of that. If you have your friend’s MMSI number in your VHF, all you do is choose the working channel you want to use, then ask your radio to call him by choosing his name from a menu. If he is in range his VHF will automatically switch to the working channel you have chosen and will ring like a phone. He just answers you using his VHF mike!

Already some computer applications are available for fleet managers to track their ships using the DSC technology. Who knows what will be available in future – linked to your cell phone while on-board?

Watch this space!

 Posted by at 8:56 am

  2 Responses to “VHF DSC”

  1. I’ve completed my VHF SRC course January 2017 – and after some difficulty got hold of the ICASA application form – not even with the help of other skippers and kayakers could we figure out how and what to fill in. I am a qualified skipper but want the MMSI number for my handheld Standard Horison HX870 when using it on the Kayak because of a variety of reasons I go out on the Kayak on my own and need the DSC function. Can I forward the application form (ICASA – MMSI Number) to anyone that can help me with completing the document?

    082 373 24 38

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