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Setting Up A VHF Radio With Digital Selective Calling

DSC is one of the best deals in town. Setting up your VHF radio with digital selective calling is simple, and it could save your life.

Raymarine VHF radio

If you've bought a VHF radio in the last few years, chances are it has a red distress button on the front. Lift the flap, press and hold the button for five seconds, and details of your vessel, your position, and the fact that you require urgent and immediate assistance are broadcast to the U.S. Coast Guard and anyone else with a DSC-equipped radio within range. The beauty of the system is that it should summon assistance even if you're unable to speak.


Never press the transmit key on the mic without a connected antenna or you could damage the radio.

When you consider that a DSC-equipped VHF can be had for about $150 and is arguably the single most important piece of safety equipment that you can have aboard, it sounds like a bargain. However, according to recently published Coast Guard figures, almost 90 percent of DSC-capable radios aren't programmed, making that little red distress button completely useless. Here's what you need to do.

Techno Two-Step

Two things need to happen for a DSC-VHF radio to work properly. First, it has to be connected to a GPS; second, the radio needs to be programmed with an MMSI number. MMSI stands for Maritime Mobile Service Identity and refers to the unique number assigned to a particular boat. Connecting your VHF to your chartplotter provides your coordinates to the radio so they can be transmitted in an emergency. With no GPS hooked up, the position of the boat must be triangulated from the transmission by multiple shore stations, reducing accuracy. Connecting the VHF to a GPS — such as a chartplotter — isn't difficult, but you must follow the instructions that came with your VHF and GPS to ensure compatibility. This is where many boaters become frustrated. In reality, it's often a matter of just connecting a couple of small wires. However, if you're shopping for a new VHF, manufacturers now offer VHF sets with GPS built in, eliminating the need to connect a GPS.

Once the connections have been made, the next step is to program the MMSI number into the VHF. An MMSI is a nine-digit number unique to the vessel, not to the radio. If there's more than one radio aboard, they must all be programmed with the same MMSI number. Obtaining an MMSI number is easy and can be done online. BoatUS Members can get a number for domestic use free of charge by answering a few simple questions. If your plans include travels to foreign ports (including Mexico, the Bahamas, and, yes, Canada), you'll need to get a Ship Station license and MMSI from the FCC.

VHF radio

Some modern VHF sets now have GPS built in which makes set up easy.

Entering the number into the VHF is fairly straightforward, although the specifics of how this is accomplished vary by make. Follow the instructions that came with the VHF to the letter. In many cases, if a number is entered incorrectly, it can't be changed without returning the VHF to the manufacturer. Check and double check that the number you entered on the VHF display is identical to your assigned MMSI before pressing the confirm button.

That's it — job done! Your VHF has just become a powerful tool to summon help in an emergency.

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Mark Corke

Contributing Editor, BoatUS Magazine

A marine surveyor and holder of RYA Yachtmaster Ocean certification, BoatUS Magazine contributing editor Mark Corke is one of our DIY gurus, creating easy-to-follow how-to articles and videos. Mark has built five boats himself (both power and sail), has been an experienced editor at several top boating magazines (including former associate editor of BoatUS Magazine), worked for the BBC, written four DIY books, skippered two round-the-world yachts, and holds the Guinness World Record for the fastest there-and-back crossing of the English Channel — in a kayak! He and his wife have a Grand Banks 32.