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Getting your VHF to "talk" with your GPS is the main challenge in getting DSC going. But it's a lot easier than most people think; invest an hour or two, and you'll have it made.

DIY Boat Project: Installing a DSC VHF Radio

Winter has set in and now’s the time to tackle those DIY projects you’ve been putting off – like mounting a new DSC equipped VHF radio at the helm. Don’t let this job slip by for yet another season. Barely 10-percent of the boaters out there have their VHF properly installed for DSC transmission, which is down-right shameful. What’s the big deal? With DSC activated, as long as you’re within radio range of the Coast Guard, if you hit the panic button and make a 911 transmission they’ll have your exact latitude and longitude, automatically. The Guard will also know all about your boat; its size, type, and other vital info they need for SAR operations.

Installing DSC is a lot easier than you might guess: all you have to do is mount the radio and antenna, then run two wires from your GPS to your VHF. You’ll also need to get a (free) MMSI number to program your radio with, and then DSC will be ready to roll.

Wait a sec – if it’s that easy, why hasn’t everyone already installed DSC? Essentially, the problem is a lack of standardization. All VHFs have been required to offer DSC capabilities for over a decade now, but no one ever defined wiring color-codes, plug, or adaptors. As a result, the chances are you’ll have to do some electrical cut-and-paste to get this job done.

Your first task will be to identify your GPS unit’s NMEA 0183 or 2000 data-out wire. Ignore black, red, and unshielded wires, and check the blues, greens, oranges, and purples. If it’s not marked, use Google to find your units owner’s manual (nearly all of them are online, at this point) and figure out what color it is. Next, you’ll need to find the VHF’s NMEA data-in line. Again, in a perfect world it would be marked, but it probably won’t be, forcing you to do a bit of research. Once you can ID these two wires, connect them temporarily by twisting them together. Finally, you’ll also need to connect the common ground.

Is your VHF now getting GPS data? It should be – but it might not just yet. If this is the case, there are two likely reasons why DSC still isn’t enabled. The first is that the owner’s manual or source you found the color coding in was incorrect—in my experience, the manuals are wrong on a regular basis. The best way to find out if this is the case is to simply swap the wires in the GPS’s “out” bundle one at a time, and see if it makes any difference (watch the display on the VHF to watch for the change; most VHFs display latitude and longitude as soon as the data begins flowing, and some others put a small satellite icon on the screen).

If wire-swapping doesn’t do the trick then it’s time to look at your GPS’s internal menu, because in some cases, you have to “tell” the GPS to output a NMEA data stream. Usually, this will be in the “settings” menu, and activating it will be as simple as changing the setting from “off” to “on”.

Everything seems to be linked up properly? Good deal. Now disconnect those twisted wires, and use crimped butt connectors to join them on a more permanent basis. Finally, use heat-shrink tubing to protect the connections.

Now that the VHF is playing nicely with the GPS, your data stream is flowing, and DSC is active, you’ll need to add in that MMSI number. This is simply an ID number which is registered in the Coast Guard’s database, so they’ll know who you are if and when they ever receive a DSC emergency transmission from you. Again, this stage of the process is a lot easier than most folks think. Just go to BoatUS’s free MMSI web site and fill out the basic data about your boat, and they’ll give you a number on the spot. Then program the number into your VHF (the method of doing this varies from manufacturer to manufacturer but it’s usually a simple procedure). Finally, mak,e sure everything is in order by doing a DSC broadcast radio check.