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Old 04-03-2015, 18:41   #61
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by rgleason View Post
Have added the last two posts to "Comments" in the Wiki.
See
DSC and Buddy via AIS. | Official OpenCPN Homepage
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Originally Posted by PjotrC View Post


Also I do not know if any popular DSC sets implement anything more than DSCDSE for Distress and for Position report... NMEA allows for more, but finally it is up to the device. So maybe no one ever generates a NMEA message for an ACK.
It is my understanding that ACKs should only be done by the official Coast Station and therefore Cl D radios are not permitted to generate them.
Ray
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Old 05-03-2015, 01:37   #62
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by PjotrC View Post
So maybe no one ever generates a NMEA message for an ACK.
What I meant here was a NMEA sentence generated and sent to the chartplotter by the radio upon reception of a DSC ACK from the aerial.

Ships stations are permitted to send a DSC acknowledge, but only after explicit approval from the coast station. The idea is to cancel an auto-repeat of distress in situation where the vessel in distress is out of range for the coast station, but is in range of another vessel, and there is no need to repeat alerts anymore (and perhaps nobody there to stop this manually).

PS.
Another case of ships station sending a DSC acknowledge is the self-cancellation (which technically is an acknowledge with own MMSI). I think this does not require the coast station's approval.
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Old 05-03-2015, 15:20   #63
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Re: OCPN support VHF DSC Position NMEA sentences?

Thanks for the clarification and additional info.

It is indeed a murky subject.

Ray
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Old 22-03-2015, 01:57   #64
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Re: OCPN support VHF DSC Position NMEA sentences?

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Originally Posted by Gypsy23 View Post
Piotr

It turns out the "NMEA" output from the GME is not RS422, not even RS232. It gets loaded down by the E120W NMEA input impedance (abt 600ohms) such that the signal is only -0.25V to +2.5V (viewed on a scope). All other "NMEA" signal sources into the E120W are at least -4V to +5V when plugged in to the E120W.

When I send captured data $CVDSC/DSE msgs back to the E120W from my PC with a USB-Serial cable which provides signals of -5 to +5, it responds correctly, the same as it did to $CDDSC/DSE. Unfortunately, it still doesn't work with OCPN.

I will have to take this further with GME or build a small interface circuit which presents a higher impedance to the GME radio.
Since this and other posts I had a reply from GME Australia, the manufacturer of my VHF GX600D. They agreed that the talker ID $CV could be changed and also offered to reduce the output Z of the NMEA cct to better drive the typical 600ohm differential NMEA inputs found on Raymarine and other NMEA devices. The GME NMEA o/p will still be 0 to +5V single ended but not get ‘killed’ by driving a low impedance. Top marks to GME for their response to this issue.



I took my radio in for updating last week and the mods were done and worked perfectly. It seems that when they developed the radio the $CV talker ID seemed appropriate and it worked OK with the Garmin plotter they had as a test bed. The Garmin uses single ended NMEA i/o hi/med impedance ccts too so the GX600D was able to drive them correctly. However, GME now see $CD is a more widely accepted talked ID for DSC and will use it for future production.



This brings us back to OCPN. As noted in my earlier posts, I have logged a request in Flyspray for OCPN to support a wider range of DSC talker IDs. I still think this is a good idea even though my particular problem has been resolved by GME. It is clear that Raymarine and Garmin accept at least $CD and $CV, but I expect they would also accept $Cx as has been proposed in the change request. It is also clear that this whole DSC subject has been implemented differently by many VHF and/or Plotter designers so OCPN accepting a wider range of talker IDs will likely resolve other problems in the future as more users hook their systems up to take benefit of these features.


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