How to Make DSC Fully Functional on a VHF Radio

Integrating GPS with VHF is a key step to ­activating DSC functionality. Here are four ways to make it happen.
VHF radio with DSC feature
Connected to GPS using one of the methods described by the author, one long press of the “Distress” button broadcasts your position and more. Courtesy Icom

To set up the automated distress function and the digital selective calling features on a VHF radio, you must acquire and enter an MMSI number, and the radio must be connected to or have an integrated GPS. Here, depending on the features of your VHF, are steps you need to take.

First Thing

MMSI stands for Maritime Mobile Service Identity, and you are far safer in your boating adventures if you have logged that number into your VHF, and networked it with a GPS source. You can register for and obtain an MMSI number at or America’s Boating Club at


NMEA 0183 was designed decades ago to allow various electronic devices to “talk to” each other. It has been largely superseded by the NMEA 2000 protocol, but most fixed-mounted GPS units offer an NMEA 0183 output pigtail with four very fine wires. Connect the GPS Data Out to the VHF Data In, and do the same for the GPS In to the VHF Out. Then, go into your GPS’s settings and activate NMEA 0183 to recognize the VHF. When complete, GPS coordinates will appear on the VHF display. Tin the wires with solder, then crimp the connections for best data transfer.

Read Next: Marine Distress Calls Explained

Chart plotter ready for DSC
Chart plotters interfaced to a DSC radio will display incoming DSC calls on-screen. This is helpful for aiding a boater in distress directly or by relaying the info. Courtesy West Marine


NMEA 2000 has largely replaced NMEA 0183 except in VHF to chart-plotter protocol and some autopilots. However, VHF companies are finally enabling NMEA 2000-VHF connectivity. With it, connecting a VHF to a chart plotter is as simple as T-connecting the NMEA 2000 cable into the vessel’s NMEA 2000 backbone. Some radios include these two parts; some require an added purchase. Either way, when it’s done, the VHF and chart plotter begin communicating, and the vessel’s geolocation is transmitted with each communication.

Internal Equipment

Some radios such as Icom’s M510 have an internal GPS module. If the radio location has a fairly good view of the sky, it works fine, and the VHF can be considered a backup navigation ­device—it’s pretty slick. 

External GPS Antenna

If the VHF doesn’t have a clear view of the sky, or if the radio doesn’t have built-in GPS, an external GPS antenna might be needed. Icom radios include a dedicated antenna connection for an optional, very small ­antenna that doesn’t require outside power. If there’s NMEA 2000 aboard, connecting the VHF to the backbone allows the radio to receive data from the network antenna. No separate antenna is required, though an extra antenna does provide ­redundant safety.