Seatalk/NMEA Raymarine/Garmin connection and ZDA sentence

[Plevier]

As a supplementary point, the brochure for the Skanti says this

With the DSC function you may use
an automatic ‘dial-through’ function
to a subscriber ashore via a coast
station without interference or use
of an operator. Just dial the number
of the local coast station followed
by the ordinary telephone number
of the person you wish to reach and
you have a connection even outside
normal mobile telephone coverage.
An automatic DSC call is much
cheaper than a normal operatorassisted
VHF call, so your communication
costs may be reduced
significantly by choosing the
SKANTI VHF 1000 P DSC.

It's repeated in the manual.

Can you actually do this? What sort of coast station do they mean?

 

[laika]

My understanding is that he is not getting time via NMEA at all, because his system does not produce the needed message, so a NMEA conversion is needed, whether this outputs UTC only or UTC and local offset. All I'm saying is that if a DIY converter was made, it would be trivially simple to add a manual local offset capability. No analogue electronics involved. It's all digital.

I'm not suggesting Troubadour stares at RS parts lists; he has already said that he cannot do the software. However, with a bit of support here I might have been persuaded to create a device that does what he needs. However, I'm not finding the posts encouraging.

No offence intended: levity rather than irony was the intended purpose of my hyperbole and you are without doubt one of the most positive contributors to this forum. I also understood the issue was total lack of time over NMEA, but was suggesting that worrying about local time could be ignored in the interests of simplicity. My point about electronics was that even the most trivial of tasks such as selecting components from high level descriptions, or selecting equivalents when a precisely specified component is not available can be intimidating. I do of course agree that adding switches is not much of a stretch beyond the main conversion task given that Troubadour isn't hot on software so I suppose the two points I was making (badly were not connected in the way that they appeared to be.

How does it know the offset? Is it just geographic (i.e. longitude based), in which case frequently wrong as Angus points out, or is it truly local (impossible surely!)?

I would bet more than the cost of a pic programmer that it's from the local time offset you manually plug into the plotter (or source of the ZDA sentences).

 

[Plevier]

My understanding is that he is not getting time via NMEA at all, because his system does not produce the needed message, so a NMEA conversion is needed, whether this outputs UTC only or UTC and local offset. All I'm saying is that if a DIY converter was made, it would be trivially simple to add a manual local offset capability. No analogue electronics involved. It's all digital.

I'm not suggesting Troubadour stares at RS parts lists; he has already said that he cannot do the software. However, with a bit of support here I might have been persuaded to create a device that does what he needs. However, I'm not finding the posts encouraging.

Angus and laika

I'm grateful to you both for your thoughts. I hadn't seen this post when I made my post no 20.
Definitely the internal clock is not updating, it won't do it without ZDA. I know from someone else that with ZDA available, in his case from a Raymarine Seatalk to NMEA conversion box (quite expensive), it does synchronise itself.
Whether that means that a real DSC distress would not pick up a UTC timestamp from GGA or GLL I simply don't know. Poor thinking if it won't.
I will try a ship to ship DSC with the clock deliberately set wrong and see what timestamp that gets if any, a +ve result would prove it's OK but a -ve result would be inconclusive.
In any case I think my post #20 will be an adequate solution. It's just a pity that checking the clock setting is quite a PITA but I will have to make it a regular ritual.
Angus, thanks for even considering doing the programming. I can build things - mainly analog - and I'm OK with high level languages but not micro code!

 

[AngusMcDoon]

What sort of coast station do they mean?

The ones that BT used to run but were shut down years ago maybe. Wasn't aware that they were ever DSC capable.

 

[Plevier]

Checked it all over yesterday.
The internal clock had drifted about 15 mins but that's over a few months since last set.
The set lets you do a test DSC transmission that routes externally and comes back to you. The received test message position was correct from the GPS but the timestamp was that of the internal clock, not the GPS time. I have to assume in the case of a distress message it would be the same.
So must keep the clock correct while I don't have ZDA.