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Old 22-01-2015, 00:36   #1
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OCPN support VHF DSC Position NMEA sentences?

This may be covered in other threads but I couldn't find it using search.

DSC equipped VHF radios can/may output NMEA sentences for responses to Position requests and Urgent Assistance calls. I understand the sentences are "DSC" and "DSE".

If I connect the NMEA output of my VHF radio to OpenCPN (V4.0), will it display the transmitting/sending ship's location and MMSI?

Can anyone provide the format/syntax of the DSC and DSE sentences pls?

Ray
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Old 22-01-2015, 03:55   #2
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Re: OCPN support VHF DSC Position NMEA sentences?

Quote:
Originally Posted by Gypsy23 View Post
This may be covered in other threads but I couldn't find it using search.

DSC equipped VHF radios can/may output NMEA sentences for responses to Position requests and Urgent Assistance calls. I understand the sentences are "DSC" and "DSE".

If I connect the NMEA output of my VHF radio to OpenCPN (V4.0), will it display the transmitting/sending ship's location and MMSI?

Can anyone provide the format/syntax of the DSC and DSE sentences pls?

Ray
Ray,

yes this is implemented.

Have look at the help manual ("?" Button) under Data connections|NMEA sentences.

bcn
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Old 22-01-2015, 16:57   #3
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Re: OCPN support VHF DSC Position NMEA sentences?

BCN, thks for the fast reply. Good to know DSC and DSE are supported. I apologise that you had to point me to the Help file for the answer, I should have tried there first but other Google searches on the subject didn't get me any closer before I asked.

The help file doesn't give format detail but does refer to the source code. I looked at the source code for clues and put together a bit of a picture of the format but I have limited recent software skills so searched elsewhere. I eventually came across an article by Eric Raymond titled "NMEA Revealed" which is very handy but did not mention DSC/DSE, however, in the bibliography he lists "Data Interface in Digital Selective Calling Class-D Radios" continuousWave: Whaler: Reference: Data Interface in Digital Selective Calling Class-D Radios which has a lot of detail about the 2 sentences gained from real-life experiments.

This is good information, along with links to 3 prior articles on the subject, which will be very useful for anyone researching/preparing to interface various radios/GPS/plotters. It is not official and has some information gaps but worth having in one's library.

Ray
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Old 22-01-2015, 21:09   #4
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Re: OCPN support VHF DSC Position NMEA sentences?

Please post your experience if you try it. Just two days ago I tried it and it did NOT work for me. I took my handheld DSC radio (with built-in GPS) and did a POSITION SEND command to my boat's fixed VHF radio. (Each radio has a unique MMSI.) The position came up on my fixed radio, but nothing came up on the OpenCPN chart or in the NMEA stream.

I don't know if OpenCPN (or the radio) only shows/transmits DISTRESS calls, or if they also do routine incoming positions. Perhaps I have to acknowledge at my radio in a certain way the sends the NMEA out instead of just dismissing it. I'm not sure, and I did not have time to experiment. Frankly I was reluctant to experiment too much because my boat is 100 yards from the water, and technically I'm only supposed to transmit when on the water. I considered walking my handheld out onto the dock, but it was icy, windy, and very hazardous to go out there.
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Old 24-01-2015, 03:01   #5
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Re: OCPN support VHF DSC Position NMEA sentences?

Hello Doc
I have not yet connected my VHF radio to OCPN but I have done some bench testing by sending appropriate NMEA sentences from my PC to emulate the VHF/Plotter situation. I confirm I was able to receive and display DSC sentences on OCPN but not yet seen a successful DCE sentence. Also, the DSC message did not come through on the first transmission of a single sentence, it required 2 transmits in close succession.

Either or both of these problems could be due to my test sentences or test rig so it is too early to be sure yet. I hope to experiment with real-life radios in the next few days and will report back then.
R
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Old 24-01-2015, 19:25   #6
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Re: OCPN support VHF DSC Position NMEA sentences?

Doc
I have made further progress with my tests, still on the bench emulating the VHF radio output.

Both Distress and Position Request work as required however I have not been able to get a Cancel Distress message to act correctly on OpenCPN. It seems to log another distress call. More work needed.

One point for you to check. AIS has to be activated within OpenCPN for these messages to show on OpenCPN as they use that part of the software to display to location of the ship/vessel. Note that the serial connection from the VHF to the PC must still be at 4800b and is not otherwise associated with an AIS device, it just needs the software operating to display it and the pop-up box with the information is an AIS info box. The message is also listed on the AIS Target List.

Ray
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Old 24-01-2015, 22:15   #7
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Re: OCPN support VHF DSC Position NMEA sentences?

Ray - Thanks for your continued updates. I am watching with interest.

FYI, I've had AIS working flawlessly for about 4 years. It comes in at 38400 on an emulated Bluetooth COM port. My GPS comes in at 4800 on a separate emulated COM port, and autopilot signals go the other direction on the same COM port. For four years, DSC has been disconnected, and I haven't really missed it. (Nobody has ever made a DSC call to me.)

I recently bought a vYacht router to translate Seatalk to NMEA and send it out via WiFi. The router also has an NMEA input that I have no use for, so I figured I might as well connect the DSC wire to it. As an initial test I connected the GPS to it and confirmed that the router sends stuff out successfully. But when I connected the DSC wire and did a SEND POS command from my handheld VHF, I did not see anything.

As I mentioned before, I probably won't do any serious testing of this until spring thaw.

Quote:
Originally Posted by Gypsy23 View Post
...Also, the DSC message did not come through on the first transmission of a single sentence, it required 2 transmits in close succession...
This is interesting and somewhat concerning. When you say it did not "come through," are you saying that it did not appear on the NMEA debug window, or it appeared there but did not show a target on the chart?
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Old 25-01-2015, 00:09   #8
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Re: OCPN support VHF DSC Position NMEA sentences?

Your system is already more sophisticated than mine! I am still hard wired although I did play with a WiFi screen synch to my Android tablet last year.

As to the questions raised by your reply:
1) You should probably check your handheld DSC-VHF to see that it is set-up to provide an auto answer to the Position Req. This is a user set option on my DSC-VHF.

2) When I mentioned it didn't come through, it failed to show on the NMEA debug window even though I saw it leaving the sending PC. There are still a couple of variables at play here so I am not too concerned yet. My emulation was via a networked port from within the same PC using another app. I want to try it via serial connection and then with my VHF before I start ringing alarm bells. I'll look at the data from the VHF too to see if it repeats any sentences.

Anyway, my initial question has been answered and proven. OpenCPN does support the DSC/DSE sentences. The question remains as to whether there are any latent problems or incompatibilities with various sending devices. From what I have read so far it is far from foolproof. I'll be testing a connection into my Raymarine E120W too so I will have a comparison.

I was going to go to my boat today but it was too hot!!!
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Old 25-01-2015, 01:08   #9
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Re: OCPN support VHF DSC Position NMEA sentences?

Quote:
Originally Posted by Gypsy23 View Post

......
however I have not been able to get a Cancel Distress message to act correctly on OpenCPN. It seems to log another distress call. More work needed.

...........

Ray
Ray
Can you catch the "Cancel Distress" sentence, by using the VDR plugin?
Please publish the file here.

Thomas
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Old 25-01-2015, 01:59   #10
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Re: OCPN support VHF DSC Position NMEA sentences?

Thomas
My experiments have been with sentences based on the research of the format by James Hebert. He has written a few articles, this is one of them continuousWave: Whaler: Reference: Data Interface in Digital Selective Calling Class-D Radios. In this he describes a sentence he trapped from a radio sending a cancel message. "$CDDSC,12,3381581370,12,06,00,1423108312,0236,338 1581370,,S,*20". His tests were done near Detroit as the lat/lon in field 6 indicates. His understanding of this sentence is that when a radio sends a distress message (the '12' in the first field) with it's MMSI (field 2) then repeats it's own MMSI in field 8, it is to be interpreted by the receiving radio and attached NMEA listeners as a cancellation.

I created a test DSC Distress message with expansion DSE for my own location in Sydney Australia:
$CDDSC,12,3380400790,12,06,00,2335015115,0925,,,S, E*65
$CDDSE,1,1,A,3380400790,00,45004400*17

Also a Cancel message with DSE:
$CDDSC,12,3380400790,12,06,00,2335015115,0930,3380 400790,,S,E*63
$CDDSE,1,1,A,3380400790,00,45004400*17

OCPN (V4) drops a Distress indicator in the correct position but when I send the cancel it seems to just register a new Distress. I have made that diagnosis by seeing that the pop-up message for the second (cancel) sentence starts a new time count.

So far I haven't actually used my radio to generate these messages. Partly because of access to my boat and partly because some of the tests would entail sending a DSC Distress message which would not be welcome by the SAR monitors or other boaters! That's one of the problems of testing this kind of thing. Jim Hebert was able to send and trap the distress messages because he used transmissions into a dummy load and in a relatively shielded area so as not to trip real-world alarms.

I hope to go to my boat in the next few days and try some of the tests with the radio connected, but not the distress message. On the other hand I will also have the opportunity to try my emulator messages into a Raymarine E120W to see how it responds to the Distress and Cancel messages.

I will trap/log as much as I can and report my findings so we decide what info might help you.

Oh, perhaps you can answer a query. During my experiments I occasionally saw a " - " black bar dropped over a previous DSC sent vessel location "green diamond" icon. I wondered whether it meant cancel but I haven't seen it across a red distress marker. Is there any listing or description of the symbols/icons used by OCPN for the DSC messages?

Keep up the good work on OCPN.
Ray
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Old 25-01-2015, 02:04   #11
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by RhythmDoctor View Post
But when I connected the DSC wire and did a SEND POS command from my handheld VHF, I did not see anything.
Doc
Sorry my earlier reply did not really address your point. I now see you sent a SEND POS from the H/H not a POS RQ from the fixed radio. I haven't tried to develop a SEND POS sentence for my emulator work but will try to get a friend to send one to me when I'm testing on board so I can trap the data exchange.
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Old 25-01-2015, 02:44   #12
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by Gypsy23 View Post
Oh, perhaps you can answer a query. During my experiments I occasionally saw a " - " black bar dropped over a previous DSC sent vessel location "green diamond" icon. I wondered whether it meant cancel but I haven't seen it across a red distress marker. Is there any listing or description of the symbols/icons used by OCPN for the DSC messages?
So many years since the original work on DSC/DSE, and so little real life testing... What I remember clearly is that I did not look at the Acknowledge sentences, so skipping them indeed is something to add to the code. Should not be difficult, but I do not have the kit today

The black bar across is likely the timeout, similar to sleeping targets in AIS. Distress targets will not timeout, but a plain Position Report probably does.
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Old 26-01-2015, 04:33   #13
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by PjotrC View Post
So many years since the original work on DSC/DSE, and so little real life testing... What I remember clearly is that I did not look at the Acknowledge sentences, so skipping them indeed is something to add to the code. Should not be difficult, but I do not have the kit today

The black bar across is likely the timeout, similar to sleeping targets in AIS. Distress targets will not timeout, but a plain Position Report probably does.
Tks for the clarification. I saw it in action today on both Distress and Position markers whilst doing further testing. It looks like it gets dropped in at about 8min duration then the msg and marker are deleted at 10mins for both types of msg.
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Old 26-01-2015, 04:37   #14
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Re: OCPN support VHF DSC Position NMEA sentences?

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Tks for the clarification. I saw it in action today on both Distress and Position markers whilst doing further testing. It looks like it gets dropped in at about 8min duration then the msg and marker are deleted at 10mins for both types of msg.
This looks like the application of the standard setting for AIS targets when not updated.
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Old 26-01-2015, 05:22   #15
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by cagney View Post
Ray
Can you catch the "Cancel Distress" sentence, by using the VDR plugin?
Please publish the file here.

Thomas
I couldn't capture a Cancel msg but I did do more testing with my emulator on both OCPN and a Raymarine E120W. The results:

1) Distress msg - The E120W creates a large pop-up with red boundary about 80% of the screen but does not drop any mark. The Op has to make a deliberate action to create a waypoint. If the msg pop-up is closed there is nothing to show where the event was until a repeat Distress msg is received. OCPN shows a smaller pop-up and drops a red marker whilst still suggesting the Op creates a WP. There is also the wonderful Red 'explosion' boundary around the red mark to ensure it is readily seen.

2) Position msg - The E120W acts in virtually the same way as it did for the Distress msg except that the pop-up is grey. OCPN does not create a pop-up for Position msgs but drops a green marker. A right click query on the marker brings up the info pop-up.

3) OCPN deletes either Distress or Position msgs after 10 mins with a warning black bar across the marker 2 mins before the delete if the msgs have not been refreshed/resent in that period. E120W messages and locations are gone when the pop-up is closed and expect the Op to have made a WP before closing.

4) Cancel Distress - Both E120W and OCPN threat this as a new Distress msg. Jim Herbet reported the Cancel msg as a new function on a SH GX1700 VHF which was accepted and acted upon by an SH GX1500S. It looks like it is a specific interpretation by SH (maybe others) because my 2013 built GME GX600D does not offer that Cancel feature. However, a review of the code in OCPN should perhaps be put on the 'do list' even if it is changed so as to ignore the Cancel and let it timeout rather than refresh/recreate a Distress when the intention is to have it deleted.

I think my emulation process is the closest I will get to testing the Distress mode or Cancel Distress, but I am confident OCPN reacts appropriately and reliably to the Distress and Position DSC messages today.
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