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Old 01-11-2015, 09:12 PM   #21
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I have Simrad NSO evo2, Simrad RS35 and RS90 VHF radios, and Sitex AIS all on the N2K network, without problems at this point (at least on the RS35 failure and multiple AIS).
What do you use for a radar with the NSO EVO?
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Old 01-11-2015, 09:15 PM   #22
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Oliver,
Perhaps but the RS35 has worked since it was installed in May. I did have a problem with the weather alerts, but got that figured out.
The NSO evo2 has an option to exclude from reporting my own MMSI number.
Henry

Yeah, really no way to tell unless you check it out in N2K analyzer. Since both VHF and other equipment is Simrad that might be why you haven't had a problem.
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Old 01-12-2015, 02:54 PM   #23
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To oversimplify, my AIS transceiver puts two types of sentences on the N2K bus: !AIVDM and !AIVDO. The first is the "normal" information received from another vessel. The second is "own ship" data that the AIS puts on the bus.

That's how my chartplotter knows I'm not about to collide with myself.

The problem comes when another receiver is connected to the N2K bus. It might receive my "own ship" data over the VHF antenna (from my transceiver) and stupidly put that on the N2K bus as !AIVDM data. The plotter may then stupidly think there's another boat on top of me and complain.

But both !AIVDM and !AIVDO have an MMSI number included in the packet.

So, in theory, the VHF radio, which knows my MMSI number, could either ignore my "own ship" transmission, or put it out on the N2K bus as !AIVDO.

Also purely theoretically, the chartplotter could see the MMSI number in my transeiver's !AIVDO packet, and likewise ignore or otherwise properly handle any !AIVDM packets with that same MMSI.

I think what I'm hearing is that I shouldn't count on either the VHF or chartplotter manufacturers being smart enough to do either of these things.

Still, it would only take one of them to solve the problem. I've put in a tech support e-mail to Garmin and Simrad asking if their devices can handle this. It'll be interesting to see if they even understand the question.
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Old 01-12-2015, 07:05 PM   #24
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What you are say is correct in principal, but keep in mind that there is no such thing as !AIVDM and !AIVDO on N2K. There are a bunch of what N2K calls PGNs which are conceptually the same as 0183 Sentences, but often quite different in their construction and how information is packaged up.

The fundamental issue is that in 0183, the whole concept of "who a message came from" doesn't exist. It doesn't exist because on any 0183 wire pair, there is never more than one talker. All you have to worry are the sentences and what they are telling you.

With N2K, there are lots of "talkers" on the bus, so anyone listening has to consider both what information is coming across the line, and also who it's coming from.
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Old 01-13-2015, 09:51 AM   #25
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Simrad got back to me pretty quickly. Unfortunately, they severely limited the length of the question I could enter into their web form, and their answer was even more succinct. Here's my question, their answer, my follow-up and their answer to that:

Q: I already have an AIS transceiver on my NMEA 2000 network but would like to add a VHF radio with AIS receiver as a backup AIS display option. Can the RS35 recognize this as "own ship" and not another boat?

A: Yes, just have to add the MMSI to the radio.

Follow-up: Just to confirm, are you saying that the RS35 will recognize that the incoming data matches its own MMSI number, and not put it out on the NMEA 2000 bus as another vessel?

A: If it has its own MMSI it will not put itself to the bus.

It sounds like the RS35 would not confuse the chartplotter with an apparent imminent collision. The issue of duplicate data still exists, and it will be interesting to see how the chartplotter deals with that.

My must-haves for my new VHF are: NMEA 2000 capable, AIS display capable. Nice-to-haves include: Hailer, Wireless remote. The RS35 is the only one with all of those, plus it's the cheapest of all the N2K/AIS units I've looked at. I can buy the radio and the wireless remote for about the price of the iCom alone.

I had no preference for Simrad going into this. I actually like iCom and Standard Horizon. But the RS35 is earning a spot at the top of my list.
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Old 01-13-2015, 10:06 AM   #26
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I have my doubts, but by all means go for it. Please let us know of the outcome.
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Old 01-14-2015, 10:03 AM   #27
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I have my doubts, but by all means go for it. Please let us know of the outcome.
Will do. ActiveCaptain's weekly Defender First discount just happens to be a B&G V50, which is identical to the SR35, along with the wireless remote mic. For a savings of $150 to $200 on the package, I ordered one.

For the record, Garmin tech support also got back to me. They asked some more questions, and suggested that it may be possible to select the source for AIS data.

It may be a while before the weather allows me to get in and hook all this stuff up, but I'll post the results here when I can.
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