GPS doesn't talk to AIS

[Critter]

Over the weekend I tried to get my new AIS receiver (NASA AIS Radar) running. It picked up a nice list of ships in the bay, but it couldn't get a GPS position from my plotter (low-end Navman, #5500 I think).

Each unit has a single wire responsible for the NMEA GPS signal, and according to the NASA manual these should be connected together at a little terminal block that came with the unit. Now I'm kind of a dummy when it comes to electronics, but it seems odd to send a digital signal through screw terminals. And only a single wire? I guess they compare its voltage to ground.

The NASA unit requires an RMC sentence IIRC; anyway, it's one of the alphabet soup of signals that the plotter claims to provide.

Any suggestions on moving forward? Do I need to program the plotter to output the specific signal that the AIS wants? Is there a better way to connect the wires? Do the two units need a more intimate common ground?

TIA ...
Max

 

[Alchera]

There's nothing wrong with using screw terminal blocks for digital NMEA signals. That's what I have for all of my NMEA connections and it works just fine. Use twisted pair or shielded wire if you can, unshielded wire can pick up noise and you may end up losing sentences. No problem if you can't, but if you notice later on that the system starts acting funny when certain components are on, that's probably what is happening. One of my backup GPS antennas can't be used when the laptop power converter is plugged in for that reason, and I haven't bothered to change it out yet. Also for that reason, you may want to turn off any charging systems when you are testing the NASA, to eliminate noise as a possibility.

Make sure your plotter has been configured to output the sentences you want, on my system (a Raymarine) you have to configure that. Then I would measure the voltage out of the plotter NMEA wire relative to the ground at the AIS radar, just to make sure there's something there. The next step would be to wire up a serial connector into a laptop so that you can actually examine the NMEA sentence, or possibly borrow a known working GPS antenna or plotter with a known working AIS output and trying that out to see if it's a problem with the NASA. Or find someone that already has a working NASA AIS Radar, take your unit down to their boat and plug it in to make sure it works. (I have one, if you want to go this route.)

Of course, you could always hire a marine tech who already has all the right equipment, but I assumed you wanted to try to fix it yourself!

- Mark

 

[Gottosail]

Nasa ais unit

I also just recently purchased a NASA AIS unit and keep having issues with my GPS (Garmin Handheld 60) and AIS interface. My situation is similiar to what Max described...the unit will be up and running...showing traffic around the Bay...and then it seems like the GPS switches back to its Default settings...the GPS signal is lost....and the AIS screen goes blank? Sound familiar? I'm curious how Max's situation is resolved....Keep us posted....Thanks

 

[Critter]

...the unit will be up and running...showing traffic around the Bay...and then it seems like the GPS switches back to its Default settings...the GPS signal is lost....and the AIS screen goes blank? Sound familiar?

No, I've never gotten the radar picture at all. Actually I do: I get a picture with the stored GPS position at the center, but it seems to be the location of the factory in England! Obviously any local traffic doesn't show up on that screen.

Actually Moonduster gave me a good lead after looking up the manual online in New Zealand (thanks Wayne!). It appears that my plotter doesn't output an NMEA signal in its default state. Hopefully I just need to tweak some settings to tell it to output the signal. Probably won't be able to get to it for a couple of weeks though ...

 

[BobJ]

If I forget to keep my Garmin (276C or 478) charged up, it defaults back to Garmin's proprietary output instead of NMEA Out. The first time I plug it back into the AIS, I have to go into the GPS's settings and change it to NMEA Out again. Otherwise the AIS doesn't know where we are.

I also had a quirky thing happen during the 2006 SHTP. At 0000 GMT (I think it was 1700 local time), the Garmin would stop outputting NMEA to the AIS and I would get that annoying alarm. If I turned both units off and back on, the Garmin would be fine again. A software upgrade (downloaded from Garmin's site) fixed the problem.

I have both the AIS and GPS's wired to the same switch on the panel. Once the GPS is on and acquired, I hit "Radar" to unfreeze the AIS.

Just to encourage you guys, I'm a bean-counter and even I could get the thing to work, so hang in there.