Thursday, January 28, 2010

Using a WatchMate with ICOM DSC Radios

I recently learned that several very widely used ICOM VHF and HF radios with DSC only accept a NMEA GGA sentence and they don't accept the standard RMC sentence that is put out by class B transponders. Unfortunately, class B transponders don't provide the GGA sentence that the ICOM requires.

This means when you are using a class B transponder as your source of GPS data, you can't also use it to feed your position to your ICOM DSC radio. That's too bad because it makes perfect sense to do this. You'll have the transponder on all the time and it has a GPS inside. Being able to also use the single-button distress feature of these DSC radios would be excellent.

So, we did a little experimenting and found that we can have a WatchMate do this for you. So starting in V3.15 of the firmware, if a GGA sentence is not found in the input stream, the WatchMate will generate one and place it in the output stream along with all the other GPS and AIS sentences. With this you can connect your DSC radio directly to the output of the WatchMate and the transponder will happily feed them both!


  1. Hi,

    I have a WatchMate 850 and don't seem to be able to link it to my icom ic-m412 VHF. Can you confirm if the internal transponder/gps will automatically generate the right sentence structure.


  2. Hi Nick, drop us a line at and we can provide you with the full answer but in short there is a way to connect to the M412