Connecting Two DSC signals into MFD12


Furuno Super Fan
I have 2 x VHF DSC radios but no-where to connect the DSC signal from the 2nd of these radios to my MFD12. Port 1 IN is occupied by my backup GP320B (primary is GP330B on the N2K network); Port 2 IN is taken up with the Hdg signal from the PG500 fluxgate; and PORT 3 IN has a combined DSC+AIS signal at 38400 baud from one of the flybridge DSC radio (which is AIS equipped). I don't always have this flybridge radio switched on.

Am I right in thinking the only way around this is to get a NMEA multiplexer and hook the lower helm's VHF DSC signal to this? If so, would it be best to multiplex with the backup GPS signal (Port 1) or the Hdg signal (Port 2) ?

Alternatively, Is it possible to bring the DSC signal to the MFD12 via the N2K network, via a NMEA-toN2K converter?

thanks and regards
There is currently no DSC support via NMEA 2000 for the NN3D system. I agree that since you have all your NMEA 0183 ports used; a NMEA multiplexer/combiner is your best option. It would need to be done with your HDG on data 2. The NMEA 1 is completely locked out with the GP320B and data 3 already has DSC coming in.
Thanks Johnny. If DSC on N2K isn't already on a list somewhere as a desirable upgrade, could you log it pls? Is there any word on when a new software upgrade is coming for NN3D? Dock rumour says all Furuno resources are diverted to new TZ product and it might be a while....hopefully NN3D isn't really being neglected !

Good point dotdun. I guess you could use the two radios into the same NMEA combiner because in most cases only one radio will be "On" or worse case the data will be the same from both so should cause no conflict.

It always takes more programmers to build a new product. There are many features the NN3D has, that have yet to be added to TZT. NN3D will have changes to the software as we move forward (Just like we have done with the Vx2 over the years) but it is now a fully developed product. TZT is just getting off the ground and will require lots of attention/development, just as the NN3D did. I will say TZT software is much more refined and hasn't had as bumpy of an initial release. The last I heard was new NN3D software was due out later this month. I do not know what enhancements it offers, yet.
Dotdun: one radio multiplex's its DSC & AIS signal outputs at 38400 baud (& receives the gps signal at this same speed): so I have Port 3 set 38400 baud to suit this. The other (non AIS) radio puts out its DSC signal at 4800 baud. Johnny might comment, but I don't think you can 'mix' these signals given their differing baud speeds....There are times when I have both radios on at the same time, or one, or the other so I'd like to find a way to always have the DSC output coming into the MFD whatever radio I'm using. I'll see what N2K sentence upgrades, if any, come with the next software revision but if no DSC over N2k, then I'll look for a simple multiplexer.
1) I'm somewhat perplexed at your need/expectation for DSC that you need to have both radios connected to the Chartplotter. Do you have a large community of buddy boats that require you to track?

2) Yes, there are 0183 multiplexers available to handle both 38.4 and 4800 inputs.

3) You mention N2k, how would you get your DSC data to N2k?

4) Will your AIS radio repeat the GPS data it receives? I ask as you are reserving the precious port 1 for a spare GPS. You could either use the AIS radio as a spare GPS connect to port 1, or disconnect the second radio from port 1 and physically connect the redundant 320 GPS if (ever) needed. (It's very rare to lose a GPS)
Dotdun: fair questions...

1. I don't always have both radios on; the flybridge radio is least used. I would prefer that whatever radio is on that its DSC function is available, for safety primarily

2. Yes, noted

3. via a NMEA-to-N2K converter...but no point unless/until Furuno makes a software change so that NN3D accepts DSC PGN's over N2k

4. It won't repeat GPS data. While it is true that gps antennae are very reliable, the 330B N2K antenna is powered via the MFD and even Furuno MFD's go down sometimes ! My redundancy strategy not only has a 2nd gps permanently installed and powered up but it is also on a seperate power supply and its outputs can be accessed on differing repeaters and displays.

I'll wait and see what if any enhanced N2K functionality comes in the next NN3D upgrade...but otherwise, a multiplexer is not a big investment and I'm now out of NN3D NMEA ports anyway....and more and more NMEA and N2k gear is coming out, so I suspect a multiplexer and/or converter will be useful at some point. Another option that has occurred to me since originally posting is to get an AIS transponder. Then no need to send the AIS+DSC signal from the radio multiplexed at 38400 baud....the DSC signal alone can be sent at standard 4800 baud. Then I'll ask Johnny what he thinks about having two DSC signals coming to the one MFD IN port, given often only one or other radio will be on at same time and if both are on, the signals should be identical in data and timing !
1 - In 8+ years of having a DSC radio, I've seen maybe 5 alerts and only one was a distress signal (and it was a mistake). I would venture to guess that >80% of the VHF radios out there either don't have GPS connected and/or the operator has no clue how DSC works. You'll get the alert whether it's connected to you chartplotter or not.