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Old 31-08-2013, 14:35   #1
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NMEA Problem

I need little help understanding NMEA 0183. The boat has a VHF/AIS receiver that receives GPS data from the Garmin and sends AIS targets to the Garmin.

The problem is that the Garmin keeps loosing AIS targets. Since the Garmin alarms on lost targets, this is annoying. If I ever have to rely on the AIS, it could get "interesting".... Yes I know never rely solely on one input to navigate....

The wiring was dine by connecting the output wires from the radio to the listening or input wires on the chart plotter and visa-versa. The connections were made using a connector strip. They are on the 'NMEA HS' settings, so the baud rate should be right.

Any ideas why the Garmin keeps loosing targets? I checked the radio, when the Garmin looses them they are still in the radio's display.
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Old 31-08-2013, 15:18   #2
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Re: NMEA Problem

Maybe the targets get out range?

Maybe the targets stop transmitting?

Maybe your antenna installation is weak?

Can you feed the same signal to any PC AIS software and check if it is the radio that loses the targets, or it is the Garmin unit.

Is there a software toggle in Garmin that allows to switch off target lost alarm?

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Old 31-08-2013, 15:49   #3
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Re: NMEA Problem

are you losing all boats, or just a few? sounds like the boats are just going out of range. if you are losing all at once then probably a lose connection.
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Old 31-08-2013, 16:12   #4
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Definitely not out of range.. I was set to a 10 mile range and the vessel was under a mile off. After loosing it, the Garmin painted it as a dangerous. And then lost it and again painted it as dangerous.

Likewise it would seem if it was the antenna I would loose the target on both the radio and plotter. That did not happen, the radio still saw the target. Nap kinda rules out the antenna.

Will recheck connections at the connecting block.

Thanks
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Old 31-08-2013, 17:21   #5
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Re: NMEA Problem

I need to know the exact model of VHF and chartplotter, and also the exact wiring - which colour goes to which. I suspect the wiring is wrong, simply because when I connected my VHF and plotter it was far from being as simple as in to out and out to in.
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Old 31-08-2013, 18:37   #6
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Quote:
Originally Posted by MarkSF View Post
I need to know the exact model of VHF and chartplotter, and also the exact wiring - which colour goes to which. I suspect the wiring is wrong, simply because when I connected my VHF and plotter it was far from being as simple as in to out and out to in.
It is a Standard Horizon GX2150 connecting to a Garmin 440. There is no multi-plexer in the circuit. It is wired using the simple in to out and out to in would work....serves me right for using logic

Thanks
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Old 01-09-2013, 04:38   #7
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Re: NMEA Problem

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Originally Posted by Snore View Post
It is wired using the simple in to out and out to in would work....serves me right for using logic
Don't have an answer for you but obviously, your logic is sound. If it was wired incorrectly you wouldn't see the targets at all.

I'm just stating the obvious saying check the connections and make sure the Garmin's firmware is up to date. I think quite a few manufacturers' early AIS implementations in plotters required updating, so make sure you're running the most up to date firmware for your device. You could always try taking another connection off the output wires from the AIS and feeding them into, say, opencpn on a laptop. If all is fine when you tap the radio end, but you get targets disappearing and reappearing when you tap the connection at the plotter end, that might be a clue. Obviously easier if you've used chocblocks rather than nicely soldered and heatshrinked connections :-). Check plotter firmware first though.
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Old 01-09-2013, 07:18   #8
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Re: NMEA Problem

Wire your AIS signal into your PC and display it on e.g. Open CPN. Output the data onto another COM and feed this to your Garmin. Watch the lost Garmin objects on your PC.

Move your Garmin to somebody else's boat and wire into their AIS feed, does your Garmin act all the same?

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Old 01-09-2013, 07:41   #9
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Re: NMEA Problem

didn't I read somewhere that some Standard radios need pull-up resistors on the NMEA interface

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Old 01-09-2013, 08:15   #10
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Re: NMEA Problem

Yes, but not the GX2150.

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Old 01-09-2013, 08:44   #11
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Re: NMEA Problem

Quote:
Originally Posted by goboatingnow View Post
didn't I read somewhere that some Standard radios need pull-up resistors on the NMEA interface

dave
Do you recall where you read this. I have the same problem with my Standard Horizon. Chart Plotter works fine but no GPS dat on my DSC Radio.
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Old 01-09-2013, 09:09   #12
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The Standard Horizon has some wiring diagrams at


http://standardhorizon.com/indexVS.c...3&isArchived=0

The one for the Garmin 400 and 500 series is at http://standardhorizon.com/downloadF...lication%2Fpdf. I am confident that this is the same as what I wired, but will check it tomorrow.

The Standard Horizon diagram does not show any resisters.

Since the Garmin firmware is current, that leaves mechanical connections as a suspect (good thing I used a block). I believe there is a way to connect a serial plug to the NMEA 0183 wiring, so I will work that angle also.

Keep the thoughts coming!
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Old 01-09-2013, 09:27   #13
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I case anyone else needs it, this is a link on how to connect NMEA to a serial connector.


http://www.maptech.com/support/doc.cfm?plid=24&docid=76
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Old 01-09-2013, 09:44   #14
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Re: NMEA Problem

So here is Standard Horizon's wiring diagram, for connecting the GX2150 to Garmin plotters :

http://www.standardhorizon.com/downl...lication%2Fpdf

Question : have you wired it like this, including connecting the black and green wires together? The latter is important. Not doing so could easily result in it working intermittently.

Oh I see Snore beat me to it with the diagram.
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Old 01-09-2013, 09:59   #15
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Re: NMEA Problem

One thing to consider is that the VHF and the Chartplotter have different purge times for inactive targets. When you lose a target on the chartplotter and still have it on the VHF check to see how long since the last message was received on the VHF for that target. The chartplotter may be purging a target after a few minutes of no traffic, but the VHF may be holding onto it for a longer period of time.

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