AMEC B600W Class B SOTDMA AIS, data multiplexing included

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

12 Responses

  1. Roger says:

    Will this allow the use of a GPS antenna over NMEA 2000, or does it require a dedicated GPS antenna?

    • Ben Ellison Ben Ellison says:

      Hi Roger, All Class B AIS transceivers are required by regulation to have their own GNSS (GPS) receiver. So what you’re asking for is not possible. However, AIS units like this one typically output GNSS position/SoG/CoG info over NMEA 2000, WiFi, and USB. You can see the PGNs in the table above as well as some configuration options like GPS update rate.

  2. Roger says:

    thanks for the quick reply. Looks like there will be GPS antennas all over the boat, One built into chart plotter, one for autopilot, and one for AIS

  3. Paliswe says:

    Messages from an AIS receiver can easily overload an NMEA2000 network and choke the communication for all other units connected to the NMEA2000. Using NMEA0183 HS will ease the tension on the NMEA2000 network and the AIS will have a dedicated connection to the MFD.
    The NMEA0183 connection is also recommended by for example True Heading, instead of using NMEA2000
    An old protocol isn’t always bad 🙂
    In my little sailing vessel I have a True Heading AIS class B since 10 years back and it works flawlessly, despite new MFD from time to time. One summer I also tested Vesper Marine XB 8000 and found it full of good things, especially it’s ability to connect to WiFi, both as a host and connected to a WiFI router. The nice thing with the latter is that I’m not limited to connect my cell phone / laptop to only one item, I can connect to all units that are connected to the WiFi router. Not all equipment offers this, I haven’t seen it on Garmin MFD for example.
    Another very useful function with the Vesper XB 8000 is that it has a standing-wave-ratio meter built in. With this I can check how good my VHS antenna works.
    I haven’t had the opportunity to test the Vesper Cortex, but with all those functions it will come with another price tag.

  4. Anonymous says:

    Paliswe, good to know… first I heard about AIS swamping out N2000….but does anybody even make a N0183 HS heading sensor anymore? And if other devices on the N2000 network that need GPS data (such as autopilot) be able to use it if it were on N0183 HS?

  5. Roger says:

    Paliswe, good to know… first I heard about AIS swamping out N2000….but does anybody even make a N0183 HS heading sensor anymore? And if other devices on the N2000 network that need GPS data (such as autopilot) be able to use it if it were on N0183 HS?

    • Paliswe says:

      @Roger GPS data is routed to the MFD and then the Autopilot gets all the information from there.
      I use the position from the MFD (Garmin 7410) and not the position data from the AIS for navigation but the MFD can be set to use the position data from the AIS instead of using internal GPS data. This because the GPS in the MFD is newer than the one in my old True Heading, with a faster update rate.

      Vesper XB 8000 has a NMEA 0183 connection. This can be used to route info from the NMEA2000 network to devices that do not have NMEA2000. I used it for sending AIS info to my MFD.

  6. Paliswe says:

    It was said to me by a guy on True Heading. Maybe it was because True Heading at that time didn’t have NMEA2000 on their AIS, I don’t know. Perhaps it’s time to reconsider this opinion.

    • Ben Stein Ben Stein says:

      I’d suggest it probably is time to reconsider this opinion. I’ve also never heard of AIS swamping N2K nor have I experienced it, including in some of the nation’s busiest ports.

      -Ben S.

  7. Ben Stein Ben Stein says:

    I’ve been thinking about the assertion that AIS might overwhelm a NMEA 2000 network. I’m not sure why it took me quite so long to connect the dots, but they finally connected. It’s simply not possible. Let’s take a quick look at how AIS works. (https://www.navcen.uscg.gov/?pageName=AISworks) There are two AIS frequencies and AIS transceivers use both of these frequencies. Transmissions are made using FM modulation at 9,600 bits per second. In reality, the same message is broadcast on both frequencies to avoid interference and congestion from disrupting transmissions. But, even if we assume both frequencies are available for separate transmissions there’s only 19,200 bits per second of throughput over the VHF transmission mechanism for AIS.

    NMEA 2000 networks run at 256 kbs or 262,144 bits per second. As you can see, there’s simply no chance AIS will overrun N2K. Even if encoding the data into NMEA 2000 PGNs added overhead there’s no chance it would be greater than 10x.

    -Ben S.

  8. Lutz says:

    I have installed a B600S last year and I have been happy with it during the first season. The only downside I found was that the USB port should not be used for operation but for programming only as it is not properly isolated (like it was on my true heading AIS receiver!) but this can be overcome by using one of the two nmea0183 ports (if not the N2K port).

    During last winter I realized that the multiplexing capability of the unit is somewhat limited: I tried to use the slow NMEA port of the unit to feed an NMEA 0183 capable listener (a display) to show the GPS position data. Surprisingly this did not work well, simply as the nmea port of the display to be used got clogged up by the data feed from the B600S. Proper analysis showed that the B600S sends its complete stream of data including the phrases for AIS (VDM/VDO) data as well over the slow port which of course no regular nmea0183 port can handle. I checked this with AMEC and they confirmed my analysis.

    So the multiplexing capabilityof the B600 series is somewhat limited. As it cannot filter any data (not even its own) out this makes the slow NMEA port useless for outputting data.

    A workaround could be to output the data over the high speed port and utilize a proper multiplexer to adapt the data stream with respect to content and speed to make it fit to any listener. and of course this will not pose a problem using N2K.

Join the conversation

Your email address will not be published. Required fields are marked *