GPS source/priority

[sailor11767]

I am on my second season on our new boat, equipped with NN3D. Still learning.

It seems that we have 3 sources of position data (GPS).

1) Connected to the NavStation NN3D is a GPS receiver that sends position information in via 0183 (I believe). That works fine, and shares the position with the NN3D at the helm.

2) Connected to the helm NN3D is an AIS transponder. It seems that this includes position data, that the NN3D can use and share. Due to errors in my understanding of my system, that's actually been my primary GPS source.

3) The primary GPS is an N2K antenna. Unfortunately, I've recently discovered that this does not work. I'm starting to trouble shoot.

So, two questions:
* First, is it possible to select and prioritized GPS sources? Once I have the N2K sorted out, I'd like it to be primary. But can I choose?
* Second, could I have the N2K source somehow disabled? I can see how I can select N2K data that is SENT, but I don't seem to be able to turn N2K connectivity ON/OFF. Is it always on, and not something for me to keep looking for?

And one other question. It seems that every time it turns on, it sets me in the South Atlantic off Africa. I have to push "ship" button to recenter. Seems this ought to be automatic? Am I missing something?

Thanks!

 

[Johnny Electron]

First, is it possible to select and prioritized GPS sources? Once I have the N2K sorted out, I'd like it to be primary. But can I choose?

Yes, you can pick your primary source selection in the installation wizard. If the selected device is bad (say like a bad NMEA 2000 GPS) then the system will autoswitch to the next good source of data it can find. This is done based on the priority below:

1) Furuno Network items providing the data
2) NMEA 2000 items providing the data
3) NMEA 0183 items providing the data

So lets say you have a Furuno FA50 AIS that connects to the network and puts out bare bones position data. If the primary source is down, it will start looking for a backup source of data and start running down the priority list. It runs into the network and finds what it needs. It will lock on and use that source until the next power cycle. When coming up the next power cycle it will again look to see if it can get what it needs from the primary selected device. If it isn't working, it will switch over again to whatever it does find (after a delay of a few mins). In this example of a bad primary GPS device, it will normally place the boat icon at zero lat and zero lon until GPS is obtained.

Second, could I have the N2K source somehow disabled? I can see how I can select N2K data that is SENT, but I don't seem to be able to turn N2K connectivity ON/OFF. Is it always on, and not something for me to keep looking for?

That depends on the device in question. For example the Airmar weather stations offer GPS and Yes it is possible to use the weathercaster software to turn off and on PGN output. It would be unlikely that someone would do that without a good purpose but it is possible.

If you have a good source of position (many times better than say your network AIS unit) via 0183, you can always choose that as your primary source until the bad unit is repaired/replaced. When the 0183 device is on, and the NavNet comes up it will go right to the working primary device (say 0183) and use it right off without delay. It won't switch to the network AIS because it is getting what it needs from the primary selected device.

Readers please note that TZT systems do this in a similar way but a bit smarter. TZT system will sense if the primary device comes back up on line during operations and will auto-switch back to the primary source when it comes online. (without power cycle)

 

[sailor11767]

Johnny Electron,

Thanks for a very complete response. I have more data to share.

With your response and the information below, I found the installation wizard and the GPS priority. And when the N2K GPS is working, the chart comes up right at the boat position. So all that is behind me. Except, it's not.

The "N2K network" on this boat is very short. It's 3 tees (total 5 connectors) with power, 2 resistors, the GPS, and the NN3D. I removed the GPS, inserted the B&G, nothing (can't see the data pushed onto the N2K by the NN3D). I removed the NN3D and inserted the B&G, nothing (can't see the GPS data). On a lark, I removed one of the resistors (so now my network has only 1 resistor) and inserted the B&G. Boom, everything works. The B&G shows data pushed by the NN3D and GPS data, the NN3D can "see" the B&G on the network, it sees and reads the GPS (GP330B, I think), everyone is happy. Then I remove the B&G, and insert the resistor, and everything stops working. The NN3D network map doesn't even show a N2K network.

I took some resistor readings. With all off, and all put together, I have 60 ohms on the data pairs. I removed all connections (so I just have the tees), I have open circuit. Either resistor gives me 120 ohms. So, resistance all seems in line.

Any thoughts? How can adding a device (while also removing a resistor) "fix" the network?

Any thoughts would be appreciated.

Thanks.

 

[Johnny Electron]

With all off, and all put together, I have 60 ohms on the data pairs.

Well a good bus with two terminations will read 60 ohms. With yours "all off" it reads good. I suspect you have two terminations on your bus you are not aware of. First off the GP330B has a termination pin option that someone might have used. If installed it will be a terminator on your bus. That pin is installed right where the GPS head meets up with the cable. (manual shows the placement). You might check that because I would guess that is one of your terminations you are not aware. You seem to have another or a problem with a remaining component or cable.

 

[sailor11767]

Well, fiddlesticks. My network fully configured is 60ohms, and with both drops on (GPS and NN3D) and no resisters it is open circuit. So I really can't see where to look for another resistor (but your tip on the GPS is nice - that's would let me remove a tee and put the resistor near the end of the network).

Yes, I have problem with a component or cable, I think. I just don't know what to start replacing. All items work with three items on the network, nothing works if any one item is removed (the classic troubleshooting of removing items until the problem goes away doesn't work here).

I can "fix" it by leaving an extra device connected and laying in the bilge. Not very stylish, but at least it makes the network work. LOL Maybe I'll find someplace to mount it in the cockpit.

 

[sailor11767]

This is coming up on a year old. In typical internet forum fashion, the OP asks a question and goes away.... So here's the end of the story as best I can remember many months later.

The bottom line is that my power came in on a Garmin power drop. A yellow cord with 2 wires, one power and one ground (and a shield? I forget). It ends in a standard 5 pin N2K plug. I accidentally found that the the data pins, that should be completely isolated, weren't. As I recall, one was shorted to either power or ground, I forget. It was strictly in the cord -- I removed it at both ends, and could ohm it to find the short. Since the pin was a dummy anyway, I grabbed it with a pair of pliers and pulled it out. It no longer kills the data on the bus.

Since then, my NN3D has had flawless GPS from the N2K data source. Case solved!

All my troubleshooting data in prior posts? Not sure what all that meant or why I had what I was reading, and I couldn't reliably repeat it anyway.

I hope this helps someone in the future.

 

[Johnny Electron]

Thanks for the follow up information. Much Appreciated! :jump