The Offshore Voyaging Reference Site

Is Your Radio Talking to Your GPS?

Even though I have been working on our new-to-us J/109 off and on for nearly two years, there are still chores on the to-do list, one being to program our new MMSI number into the VHF—I did our AIS transmitter as soon as we got the boat.

Luckily for me, although disturbing to find out, there was no MMSI number in the VHF, so the two previous owners were forgoing a big safety feature.

I say luckily because radios and AIS transmitters sold in the USA can only be programmed once, or at most twice, at least without help from the manufacturer. Who thought that was a good idea? Homeland Security, as I understand it. Don’t get me started.

Anyway, I had assumed that the radio was at least getting GPS positioning sentences, since there were two wires leading from the correct terminals on the radio to…the wrong terminals on the source.

I hadn’t changed that, so clearly it had been that way for years since the “professional” hooked it up and never bothered to check it worked! Saints preserve us from “professionally maintained boats”.

The fix took minutes and was confirmed when “GPS” came up on the panel.

With these two problems put together, the nice red distress button on the radio was for decoration only.

So I have made a mental note to always check the display for that indicator when I turn the radio on, since it would be easy for the wires to get disconnected or a parameter to get changed in the source GPS (say BAUD rate), rendering this important feature useless.

By the way, while this crappy little radio is adequate for our needs, if I we were still going offshore and cruising countries where DSC is used more than it is here, we would be replacing it. More here.

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Philippe Candelier

The radio is actually not really talking to the GPS, rather listening NMEA sentences. It does not send back messages.

Jean-Louis Alixant

Hi John,
Thank you for pointing out this safety-critical verification.
For those that will look into it, be aware that it may be necessary to adjust the communication protocol, specifying the words to exchange, and setting baud rate. The point is that if it appears not to work, it may need to look a little deeper in the system. We followed instructions provided by a local electronics specialist.
By the way, more recent VHF sets equipped with their own internal GPS antenna may also benefit from an NMEA connection. In our case, the VHF mounted at the nav station was systematically losing GPS signal over a certain heel angle range (not straightforward to find out). Connecting it to the NMEA network solved the problem.
Our set allowed the VHF to listen to NMEA sentences, but also to broadcast on it. So in the event we would lose all NMEA-connected GPS sources (such as in power conservation mode), the VHF would add yet another one.
Finally, the “one-time MMSI programming” also applies in other countries, such as France 🙁

George L

the resetting may not be such a big deal, in some cases you can request a reset code on a website and then you can reset it yourself. At least works like that on some handhelds.