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Chuck Husick: Techno-Talk, January 2007 BoatUS Magazine -

DSC/VHF/MMSI

Help When You Need It


Would you spend $200 to save your life? That’s the cost of a VHF/DSC radio, the most effective emergency communication device you can put on your boat. I believe you owe a duty to yourself and to everyone on your boat to install a DSC radio, connect it to your GPS and learn how to use it.

Until recently virtually all radio communications began with a voice hailing call on channel 16, the international calling and distress channel. Hailing on channel 16 works fairly well, except when a call is blocked by other callers. Although inconvenienced, we repeat the call, adding to the congestion and blocking other calls. However, a distress call that is blocked or made incomprehensible doesn’t just cause temporary inconvenience. Lives can be lost if the message does not get through immediately.

The DSC system avoids the major deficiencies of channel 16 voice hailing for both distress and routine calling by substituting a digital message, similar to the text messages used on cell phones, for the channel 16 hailing voice hailing call. The brief, typically 1/3rd of a second, messages are sent on channel 70, which is reserved exclusively for DSC signals. There are no voice calls on channel 70 and the brevity of the digital call virtually eliminates interference from other users. DSC calling, combined with the Coast Guard’s DSC-based Rescue 21 system and the DSC radios on virtually all Coast Guard boats and on tens of thousands of your fellow recreational mariners vessels will create an incredibly valuable safety net.

In addition to its value for emergency signaling DSC hailing also makes routine communication as easy as making a telephone call. To call a vessel or shore station simply select a working channel, enter the Maritime Mobile Station Identity (MMSI) of the station you want to call and press the enter button. Your DSC call tells the station you are calling who you are (your MMSI) the working channel you wish to use and your position (position can be optional for routine calls).

You can buy a Class D DSC radio, the type with two separate receivers, one permanently tuned to channel 70, the DSC hailing channel for the price of a dinner for four at a nice restaurant. The Maritime Mobile Service Identity number (MMSI) registration number you need to be identified on channel 70 is available at no cost by phone or on line from BoatUS (At last count BoatUS has issued more than 35,000 MMSIs).

To obtain the most value from your DSC radio for emergency signaling and routine signaling it must be connected to your boat’s GPS or Loran C receiver. Be sure that your radio is properly connected to the boat’s GPS or Loran C receiver. Making the connections is not difficult, you need connect only two wires from the GPS to two wires from the radio. Whether you make the connections yourself or have someone do it for you be sure to verify that the position information is transmitted in your DSC hailing calls. Remember, in an emergency five minutes saved can save a life.

DSC calling has obvious value in the hand-held radios many boat owners carry as back-up for their fixed mount sets and when on their yacht’s tender, a canoe or kayak. At present there are very few hand-held radios that offer DSC capability. However, today’s GPS receivers are tiny, require little power and are cheap enough to make including them in a hand-held a practical option. It’s virtually certain that the safety value of DSC will make a distress button available in many if not all newly designed hand held radios.

Many boaters routinely verify the operation of their radios by making a “radio check” call. To perform the test with a DSC radio select a working channel (not channel 16), enter the MMSI of a friend’s radio or that of a marina or yacht club and press the “enter” button to send the DSC hailing message. If the called station receives your call it will usually respond with a digital acknowledgment message that will appear on your radio’s LCD screen and then switch to the working channel you selected for voice communication. Under no circumstance use the distress key to make the radio check call.

Go to www.boatus.com/mmsi for information about obtaining your MMSI. Click on the DSC Radio Tutorial to view “Can You Hear Me Now” a BoatUS Foundation / U.S. Coast Guard radio communication briefing for the recreational mariner.





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