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Ben E

Direct DSC VHF calls to AIS targets, a NMEA 2000 standard??

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This interesting comment conversation has been pulled off the Simrad Go7 and B&G V7 entry, and I hope we can figure out if this is a standard or proprietary feature:

First impressions are good, apart from the lack of radar support. Page 88 of the Operator manual shows a nice user interface to support making DSC calls to an AIS target over NMEA 2000, complete with a change channel option. Not only that, it uses the standard N2K PGN 129808 so it works across brands.
NMEA 2000 using standard connectors and no NMEA 0183 connections!
Posted by: norse at March 31, 2015 8:31 PM | Reply

norse, let me add this:
NMEA2000 PGN 129808 signals an *incoming* DSC VHF call to, for example, a MFD - which can then display the location of the caller on the chart and/or show a notification message (I doubt that the latter has much use as the VHF radio is already ringing loud enough to wake the dead).
A standard NMEA2000 PGN for communication in the other direction, to instruct a VHF radio to set up an *outgoing* DSC call i.e. by using an MFD, is not yet defined. So Navico must do this via a proprietary PGN which won't be (can't be) supported by other manufacturers.
Not to take away from these nice features, though. It's the best Navico could have done given the blazing speed of to define new PGNs ;-) ... should I mention that the above PGN is still listed erroneously as "12808" on their web page and this hasn't been corrected for 5 years now?
Posted by: Henning at April 1, 2015 4:36 AM | Reply

On second thought: Maybe a standard PGN for an outgoing call has been defined and NMEA's website just hasn't been updated?
Does anyone know? Or knows how to get this information?
The GO7 manual, even though it has 122 pages, does not list supported PGNs.
Posted by: Henning at April 1, 2015 4:50 AM | Reply

Henning, look in the installation manual.
Posted by: Ben in reply to Henning at April 1, 2015 7:37 AM | Reply

OK, I did and it says
130842 SimNet DSC Message
The standard PGN numbers go up to 130578 (Vessel Speed Components) so I believe the range above are proprietary messages - including 130842.
Posted by: Henning at April 1, 2015 2:51 PM | Reply

Yes, I think you're right that the 1308xx range are proprietary PGNs, and it's an interesting bunch. My favorite mystery PGN = 130839 Pressure Insect Configuration ;-)

I doubt that NMEA's online PGN list is completely up to date...
...but also have not heard of a new PGN that handled DSC direct calling.
Posted by: Ben in reply to Henning at April 1, 2015 7:29 PM | Reply

The PGN list for the Go7 needs an edit check. There are several listed multiple times with different labels, which is odd. 130842 is one of these, however we know what that one really is, despite two misleading labels -- It is the proprietary PGN which enables AIS class B static data which Navico used at first. Now they use the standard PGNs of 129809 and 128810, although they still support 130842 for those who have the NAIS-300 transponder.

Since you probably won't take my word for it that 129808 is the proper PGN for DSC calls and that it works both ways, I'll have to find something definitive on the web. That's a bit tricky because it's a hard PGN to understand and there was a technical corrigendum to it in 2013 which isn't so easy to understand either.
Posted by: norse in reply to Henning at April 1, 2015 8:29 PM | Reply

OK, first of all, Kees has illustrated that Simrad proprietary PGN 130816 was used previously to make DSC calls from an MFD to a Simrad RS82/87 VHF.
Some documentation from NMEA you could look at is here:
(page 40/52)
Unfortunately, it implies that all DSC calls are distress calls. However, these fields
6 Proposed Rx Frequency/Channel
7 Proposed Tx Frequency/Channel
16 Calling Rx Frequency/Channel
17 Calling Tx Frequency/Channel
do imply that this PGN can be used both to set up a DSC call and report on a DSC call received.

and, the later information:
(it doesn't add to this discussion)

The bottom line is that Garmin has implemented the DSC call to an AIS target years ago and now Simrad can do it too (key point: over N2K using standard PGNs).

So it can be done, but how do they do it? The suspects are
PGN 129808, DSC Call Information.
PGN 129799, Radio Frequency/Mode/Power.
Posted by: norse at April 2, 2015 1:59 AM | Reply

10 Replies

  • I've been studying MFD and VHF operator and installation manuals and their PGN lists. Users are not the only ones confused. The big name reputable manuafacturers are too, since they give conflicting information.

    DSC VHF radios have been around long enough that there are many in use. However, we know that more than a few of them are not hooked up to a GPS and that many users do not use the nice DSC calling features. The easiest way to hook up a GPS to your VHF is by using NMEA 2000.

    AIS is another aspect of VHF. Most AIS receivers or transponders have a little display. The easiest way of getting a larger (more useful) display is to hook the AIS up to an MFD. The easiest way to do that is by using NMEA 2000.

    Once you have your GPS, VHF, and AIS connected to your MFD using NMEA 2000, if all goes well your MFD should collect a list of DSC callers and AIS targets and show you their MMSI number. With the MMSI number, you can go to your VHF and enter that number and place a VHF call. So far, this should work with any N2K VHF because all of them (VHF and AIS) should support the PGNs which tell the MFD the MMSI number.

    Some manufacturers have taken it a step further, Garmin first and now Simrad, and that is to use the MFD to set up the VHF call so that you do not have to type in the MMSI number. You still have to use the VHF to make the call, but without the nasty enter-a-long-string-of-digits step. Simply select the boat to be called from the list of DSC or AIS contacts which the MFD has collected (or that you have entered).

    NMEA 2000 has two PGNs which are used by the MFD and the VHF to communicate: 129808 and 129799.

    129799 is very simple and general.
    129808 is not simple and is specifically for DSC calls.

    129799 has fields for Rx and Tx Frequency in Hz, Radio Channel, Mode, and Channel Bandwidth.
    This looks like it could be used for a VHF or other radio to report its status to an MFD, but it looks too sketchy (without more information at least) for use by an MFD to control a VHF.

    129808 is much more complex, which is expected because it is for use with DSC VHF and DSC is complex.
    It's hard to say exactly how this is used or should be used without more information.

    I've looked through manuals, etc. Let's start with the Icom 506 VHF. That transmits (onto N2K) the PGNs 129808 and 129799, DSC info and VHF status. The Icom 506 VHF does not receive (from N2K) either PGN. Now take the Lowrance HDS-8 Gen-1, it receives the N2K PGN 129808. Therefore the MFD should plot positions and know MMSI numbers of DSC calls to the VHF.

    For the advanced level, where the MFS should be able to set up the VHF to make a DSC call, look at the Garmin VHF 300. It receives (N2K) 129808 and transmits (N2K) 129799, same as the Icom 506. However, some PGN lists for this radio also list it as transmitting (N2K) 129808. That would make sense, but it gets more confusing...

    One Garmin N2K tech document lists the MFD 4x1 and 5x1 as receiving 129808 and 129799 and not transmitting either. Looking at the manual for the 500 and 700 series, it says the MFD receives 129808 and 129799 and transmits 129799. Garmin says this MFD will have the call target feature with any Garmin VHF, despite the conflicting PGN lists.

    The Simrad RS90 VHF uses both 129799 and 129808, although they don't say which are transmit and which are receive.

    So there you have it, it's something to do with 129799 and 129808, although we're not sure what, and neither are the manufacturers ;-)

  • I've just re-added PGN 129808 support to CANboat, and I'd love for someone to test this as I'm stuck in RS82 land (which uses ancient 2004 era private PGNs). I must say that 129808 is not (ahum) the best designed PGN. It does pass on all DSC information available in the radio datagram, just not in NMEA 2000 style. You can see the DSC data format (which is rather different) shine through. Fields overlay depending on other fields instead of including both fields and then not using unused fields.

    Anyway, the real reason I wanted to comment is that Simrad, Fusion and other manufacturers overlay multiple datagrams over one PGN. The way they do this is that the proprietary PGN (like any proprietary PGN) starts out with 16 bits of data that state this is a 'brand X' PGN, which means that any other brand will ignore it. Then they use a 3rd byte that indicates a further level, as a 'sub command' if you will. I think they use this in order not to use up the entire PGN space. Simrad have used (and still do) PGN 130842 in the past for the proprietary version of the missing Class B AIS PGN. So you could argue that having that in the list multiple times is an artefact of them removing what they use it for.

    See for all information I've been able to learn so far.

    If someone is able to log the NMEA 2000 data during a Garmin or Navico DSC call, please send that to me so that I can examine the data exchanged.

  • Since Raymarine has new VHF radios with NMEA 2000 support, I thought it would be interesting to see how Raymarine lines up on this question. The new models are Ray50, Ray60, and Ray70. Ray70 includes an AIS receiver. If you want easy, having GPS and AIS built into your VHF reduces the required connections. Oddly, the manual doesn't say much about AIS beyond how to turn it on, so I don't know if calling AIS target from this VHF/AIS combo is a feature.

    For all of the new Ray VHFs, the PGN list is the same for the two PGNs in question here. They all transmit 129808 and none receive it. None list 129799 at all.

    Raymarine added support for DSC over NMEA 2000 in Lighthouse II V9.45. Reading the manual, that means the DSC Distress Alerts and responses from DSC Position Requests that you send can be displayed on the Raymarine MFD. There is no mention of calling, and although Raymarine MFD has a Buddy List, there is no mention of calling them either.

  • I just installed a B&G Zeus2 plotter, a Vesper XB8000 AIS, and an Icom 506 (model with NMEA2000 capability, but without AIS built in). All of these are networked together using NMEA2000. The Icom screen and the Zeus2 both display the AIS targets. On the Zeus2, you can tap the target, and all of the ship information comes up as a popup. At the bottom of the popup is a "Call" icon. It's greyed out a bit, which probably reflects it is inactive as nothing happens when selected. I suspect when combined with a B&G brand VHF, this easy-call feature would work. With the Icom 506, it does not (although I was told by B&G that it would prior to purchase, and yes, I know, I should have asked Icom instead). Icom PGN does not apparently support receiving a call request. Any advice on what to do to make this work? Other than toss my new Icom?

  • Very interesting, Michael! And first knock I've heard on Icom 506, which I hope to try soon myself. Comments:

    1. Isn't the Icom showing AIS targets with an easy way to make direct calls?

    2. The Simrad RS35 with AIS rx does not have any facility for easy direct calls to AIS targets, though it's been promised and the "call" button you're seeing on Zeus2 anticipates it. But RS35 software hasn't been updated since 2013!

  • Ben, I am also wrestling with a faulty antenna splitter, so have not tried the direct from radio approach yet. As written in the manual, it's just a few more buttons to push, knob to turn, etc., and should work. Not exactly what I was sold on when purchasing the B&G system.

    Regarding the Icom 506, I have always been an Icom fan. Doing a large electronics upgrade on my 12-yr old boat, and the old radio did not even have DSC. When the antenna is wired direct to the VHF, this radio had incredible clarity and reception. I also like that the microphone is a speaker when not transmitting. No more leaning into the radio to hear in high noise situations, as now can just put the mic up to my ear.

    Only other possibility to make it work that I can think of - and I am clearly out of my league here - is hooking up the NMEA0183 from the Vesper AIS to the VHF, and hoping that the Zeus2 can send a PGN to the Vesper to call the VHF using that protocol. The radio specs say that is how Icom 506 is triggered to make a call when wired to their own transponder.

    Now that I look further into the M506 documentation, I see on page 90 of the instruction manual that the VHF can transmit PGN's 129799 (radio frequency, mode, power) and 129808 (DSC call information), but not receive these same PGN's. My guess is that Zeus2 has ability to send these PGN's, but Icom cannot receive them? Wouldn't this just be a simple software issue for Icom to fix?

  • I am still trying to understand - from B&G/Navico Technical Support - how the Zeus2 works. They now say it is proprietary protocol. The installation manual doesn't list 129799 as either received or transmitted. It does list 129808 as receive only. They also list as receive only, a 130842 SimNet DSC Message that someone referenced above.

    Although they promised this would work prior to ever buying the equipment, addressing my issue is not their concern in the near future. After I posted about the problem, a half dozen others with B&G VHF and B&G Zeus all commented that none of their Zeus direct call to DSC features worked either. B&G Navico says they are working on software to get that to work.

  • From page 95 of the Zeus2 operator manual (But I also have the IC-M506 with NMEA-2000 and AIS and the Vesper 8000XP and the Zeus2 12 and this functionality is not working so far for me either)(The manual must be "prospective"):
    "If the system includes a VHF radio supporting DSC (Digital Select Calling) calls over NMEA
    2000, you can initiate a DSC call to other vessels from the Zeus2."
    "The call option is available in the AIS Vessel Details dialog, and in the Vessel status dialog activated from the Tools panel."
    "From the Call dialog you can change channel or cancel the call. The Call dialog is closed when the connection is established."

  • Unfortunately what they may actually mean is "a Navico VHF radio supporting DSC..." I just updated the test Simrad RS35 on Gizmo and now I can place direct DSC calls to AIS targets:

    I'll ask Navico if this feature should work with your M506 and/or other radios.

  • Are there any updates on the feature of direct DCS calling using AIS. I read the ICOM M506 manual and it seems that they support this feature, but only if the radio is connected to an ICOM MA500TR. I was wondering if any radio could receive AIS data over NMEA2K and still conduct a DSC call directly using the AIS data?