In this thread we can see the confusion... but I had hoped the manufacturers would get their stuff right....
So here to clear some of the things up:
1. DSC vs
AIS. There are no AIS receivers/transceivers with DSC. The only time these two meet is when a DSC
radio also has AIS. Plotters can combine these, see point further below.
2. DSC always has accurate
GPS position. This is the reason that every DSC equipped
marine VHF must have a position either from internal
GPS or receive position from
NMEA. Distress calls are the most important DSC call and would be useless without position.
3. Position polling is done by SAR after they receive your distress call. This can be a DSC distress but also
Epirb etc. All they need to know is your MMSI and general vicinity. This is either sent directly in the distress call or it is triangulated by satellites receiving your
Epirb transmissions that have no embedded GPS position.
Your DSC radio should have a GPS position fix on it’s display and have DSC position polling reply set to AUTO, which is default. SAR can
poll your position from far away, using very high and powerful shore based antennas or from airplane and helicopter. This can
work over hundreds of miles.
If you had activated an Epirb, it will also transmit a 121MHz homing signal that can be traced with direction finders but it is a dated method and DSC distress calls do not support it at all. This is why DSC position polling is more than just for buddy
boating.
Also, there are DSC man
overboard gadgets that you clip on your life vest and will transmit DSC distress
MOB calls to all DSC equipped vessels in range.
4. Official NMEA2000 PGN’s are 129799 radio frequency, mode,
power and 129808 DSC call information. I found both my
B&G V50 and Standard Horizon GX1850 transmit both PGN’s, but in mysterious, not yet fully debugged ways.
5. On your modern plotter you have a “ships list”
screen. This lists all ships known to the plotter from every source available: AIS, DSC and ARPA/MARPA. In this
screen you can normally filter to see only AIS or only DSC etc. When you select a ship you get all it’s data that is available.
When my
B&G plotter detects my B&G radio, it enables a “Call Ship” button on that ship information screen. It uses vendor proprietary PGN’s to set up the radio for a DSC individual call. When I turn that radio off, while keeping the other radio on, the button is disabled. Clearly no standard for this.
You can show all of these targets on your chart. I have been testing this and think I saw both radios successfully plot a DSC target... but not always. When a received DSC position is from my own MMSI, the B&G radio sends the PGN but the Standard Horizon does not. My plotter doesn’t plot either way and I tested that with a position several miles away from me as well. These messages must be filtered, which means that when you receive it from your handheld that is away from the mothership, it does not get plotted. But the radios know it and can navigate to it because they have GPS after all.
I am scanning my
NMEA 2000 network using both Maretron and Actisense
gear. I spent hours yesterday updating everything, fighting with Windows drivers, updating firmware and applications etc. It’s all running the latest now and knows about the latest manufacturers like Yacht Devices.
During all this I found some conflicts in my
network so I had a lot of diversions to deal with.
6. The problems with Standard horizon and NMEA2000 are serious and well documented. They are not only for the GX1850 series but also the GX6000. The question is if it’s improved with the new GX2400. I found no info on that radio around NMEA2000 support yet.
As it stands now, you need to switch the radio and NMEA2000 or GPS on in a particular order or it won’t work at all. It’s ridiculous and SH’s claims of this being normal are outrageous as other radios demonstrate perfect behavior. Besides “living with it” the only solution I see is feeding the radio with NMEA0183 data besides the NMEA2000 connection. We had this mess before when plotter manufacturers started implementing NMEA2000. My problem with the US support group for SH (the manager) is that he straight out lies to customers. Ben Ellison of Panbo tells me he is probably instructed to do so from higher up but he knows all these guys and I simply can not tolerate someone lying to me like that.
I not sure if I covered all the issues mentioned in this thread so let me know if I missed something. As soon as I find more time and get a buddy with different MMSI to help I will be testing again
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