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  #1  
Old 02-27-2012
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Does AIS require GPS input?

Hi all,

I've recently picked up one of these ICOM MXA5000 receive only AIS units. Under $200 for a name brand like ICOM made me bite the bullet.

I'm not sitting here trying to wire everything up. I've got a the radio cabling handled...but now wondering what is the best way to wire to the Raymarine C80 plotter.

Would I simply take the Data Out (NMEA 0183 @ 38400 baud) to the plotter at the helm? Or do I also need to give the AIS a GPS data feed for it work properly (so from NMEA/Seatalk junction box, 1 nmea data feed to the AIS box input, then 1 output wire from AIS box to plotter).

My GPS is directly wired via seatalk to the plotter already, and is repeating down to the NMEA/Seatalk junction box I've got down below for the purposes of sending data to the laptop.
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Quickly. For AIS you need to get GPS data to the AIS. Most transmit/receive units have a dedicated GPS as that is required by law. For your application a NMEA talker feed on your Chart Plotter goes to the AIS to give it GPS data presuming it did not come with a dedicated GPS. The output of the AIS goes to a high speed NMEA input on your chart plotter. Since you don't transmit you don't have the last feed, the heading data from the gyro-compass. This is not a required feed for a class B AIS.
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Quote:
Originally Posted by svzephyr44 View Post
Quickly. For AIS you need to get GPS data to the AIS. Most transmit/receive units have a dedicated GPS as that is required by law. For your application a NMEA talker feed on your Chart Plotter goes to the AIS to give it GPS data presuming it did not come with a dedicated GPS. The output of the AIS goes to a high speed NMEA input on your chart plotter. Since you don't transmit you don't have the last feed, the heading data from the gyro-compass. This is not a required feed for a class B AIS.

Thats what I needed to hear. Also, since the AIS is connected to the radio, do I need to have a separate set of wires to the VHF for emergency/distress DSC button?

Last question, I purchased a length of 28gauge wire (6 in the bundle)...so is it possible to plug in 2 wires each to the NMEA out of the seatalk/nmea junction box...2 for the AIS, 2 for the VHF for emergency distress/DSC? Meaning can I plug multiple "listeners" to the NMEA out of the seatalk/nmea box.
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Old 02-28-2012
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Quote:
Originally Posted by night0wl View Post
Thats what I needed to hear. Also, since the AIS is connected to the radio, do I need to have a separate set of wires to the VHF for emergency/distress DSC button?

Last question, I purchased a length of 28gauge wire (6 in the bundle)...so is it possible to plug in 2 wires each to the NMEA out of the seatalk/nmea junction box...2 for the AIS, 2 for the VHF for emergency distress/DSC? Meaning can I plug multiple "listeners" to the NMEA out of the seatalk/nmea box.
Lets make sure we are on the same page. I made the assumption that your radio and AIS both talk NMEA 0183 as most of the equipment around today does. If that is true:

1. The NMEA 0183 specification states that any NMEA "talker" can power up to four (4) "listeners." So you could take a "talker" wire off your junction box (which I presume has the GPS data as pretty much they all do.) You would be wiring the "listeners" in parallel - the NMEA + out from the talker goes to the NEMA + in on both listeners - same for the NMEA - out it goes to the NMEA - in on both devices. BTW if you have not yet purchased the junction box you can most likely get the same data from either your chart plotter or your autopilot computer (presuming you have one.)

2. Many older NMEA devices can daisy chain. That is you can feed NMEA into the device and it will repeat the NMEA sentences on the NMEA out of the device. Coupled with the 1 to 4 ratio this gives you lots of NMEA connections. Consider your chart plotter can power at least four devices, each device can power four devices, each of those can power four devices and so on. The limitation is that some manufacturers Insert WHY I HATE RAYMARINE HERE violate the specification and don't repeat the input sentences (the technical name of a NMEA message) on the output side. There are several possible reasons for this. My explanation is that (unnamed marine electronics manufacturer that I hate) does this so that they can rip you off for more unnecessary "conversion" boxes.

3. Note that there is no real relationship between the AIS and the Radio. You are just trying to get the GPS sentences to both of them. I don't understand why the AIS is connected to the radio unless you are feeding data through the AIS receiver into the radio. Can you please clarify?

4. In a pure NMEA 2000 world plugging the Radio and AIS into the NMEA 2000 bus would make this all happen auto-magically.

Last edited by svzephyr44; 02-28-2012 at 12:03 AM. Reason: substitute junction box for chart plotter
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Ok...progress. I dont have enough wire to finish the project tonight.

But I *think* I followed the instructions you gave. From my NMEA out on the Seatalk/Nmea box, I plugged in 2 wires in each the + and the - ports (So, 2 + and 2 -). Back at the nav station below, I took 1+ and 1- wire and hooked it into the ICOM M422 radio. *VERY* weird setup Icom has, with 1 single wire handling both nmea polarity wires. The wire in the core was for the + and the shielding was for the -. It took me hours to figure this out. Nevertheless, the result as follows:



I took the other + and other - and put them into the ICOM AIS unit. As I mentioned before, I dont have enough 28 gauge wire to run from the output of the AIS to the NMEA input (38400/high speed) on the plotter. Need to make a run to Boat Owners Warehouse or West Marine tomorrow to finish the job.

So, today's lesson was to *FINALLY* hook up my VHF for DSC distress which will broadcast my GPS location. Woo hoo...?
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The more I'm reading the more this (receive only) AIS unit seems to *NOT* require GPS input. Only the plotter or unit displaying the data requires GPS!
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Quote:
Originally Posted by night0wl View Post
The more I'm reading the more this (receive only) AIS unit seems to *NOT* require GPS input. Only the plotter or unit displaying the data requires GPS!
That is correct
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Old 02-28-2012
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Hey,

You are correct that your AIS receiver does not need GPS data. Since you are not broadcasting AIS information, it doesn't need GPS. It will SEND the AIS data, which includes location information on a vessel (LAT/LONG, as well as COG, SOG), to another device, like a chart plotter. That plotter needs to have GPS information it can calculate CPA and other information.

Your ICOM DSC VHF radio SHOULD receive GPS data so that you can broadcast DSC alerts.

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Quote:
Originally Posted by night0wl View Post
The more I'm reading the more this (receive only) AIS unit seems to *NOT* require GPS input. Only the plotter or unit displaying the data requires GPS!
As was pointed out above this is correct. I forgot that we were in the receive only mode. In the US by law the AIS has to have a dedicated GPS attached if it transmits. This raises an interesting question. Who does the CPA calculations, the AIS or the Chart Plotter? I will have to delve into this a little more to figure it out.

BTW most AIS transmit capable units output their GPS data on the NMEA high speed buss. So you don't actually need to have another GPS.
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Old 02-29-2012
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Well, its hooked up to get GPS and multiplex it back to the plotter. I guess there are now two routes for this data back to the plotter.

Got everything dry-fit today for AIS data to helm. Pretty neat, Beneteau or my dealer even included the NMEA cable to plotter (which I had bought an extra one of, not knowing it was prewired). That saved me $40 and having to fish wires down the pedestal. So, only now have to butt-splice/shrink tube the wiring connections and fish the wires to make it all clean.



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