Watch out! If your VHF does not have mmsi number DSC does not work

I must admit that in the 5 or 6 years that I have had a dsc set fitted the only time it has been used in that mode is when I have heard a panpan call or, on several occasions a general call to all ships to place an alert about inclement weather. We only sail in Greece, largely in sunny and benign conditions.

However last trip out we set out from Paxos in 25 knots plus with a large sea running on the back of a moderating forecast. Needless to say it did anything but moderate and eventually just past the tip of Anti Paxos we were in 40 knots plus and the seas were building to 5 or 6m.

The third or fourth time the DSC went off I actually listened to the bloke talking at the other end before cancelling the call. Turned out they were trying to talk to me to see if I really wanted to be out in that weather! :) Seems they'd been tracking me on AIS and had dialled in my mmsi to contact me.

Up till then i'd never bothered with DSC.
 
The technology behind DSC is obsolete early 1980s technology. IMHO DSC had only one single advantage, the little red button that transmits lat/long and your MMSI no in a distress situation. Other then that it's utter rubbish for routine call use. Its hard to believe in 2013 we are still using WWII analogue technology for voice comms instead of a compressed digital voice protocol on the marine VHF band. DSC has no provision for messaging, just call instigation. Marine VHF needs a digital text messaging protocol as well as digital voice comms.
 
My wife wouldnt let me use the VHF radio until I obtained a license. I did the course and obtained a license within a few weeks of buying the boat.
I had done a little reading beforehand. So the course and the exam was not particulary challenging. Quite an enjoyable day in fact. I think everyone on the course passed.


When I bought the boat 5 years ago the VHF set had no MMSI entered so presumably the previous owners had it erased, or more likley never entered a number.
It's illegal to use a VHF without an operators license but no one seems to care about that even though the fine is potentially severe.



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oceanfroggie said:
The technology behind DSC is obsolete early 1980s technology. IMHO DSC had only one single advantage, the little red button that transmits lat/long and your MMSI no in a distress situation. Other then that it's utter rubbish for routine call use. Its hard to believe in 2013 we are still using WWII analogue technology for voice comms instead of a compressed digital voice protocol on the marine VHF band. DSC has no provision for messaging, just call instigation. Marine VHF needs a digital text messaging protocol as well as digital voice comms.
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The trouble with digital voice is that it does not degrade gracefully - doesn't matter for broadcast entertainment but not good for something safety critical. An analogue signal can be understandable almost down to the point where it disappears into the noise floor but the digital signal would have broken up to R2D2 long before.
 
maby said:
The trouble with digital voice is that it does not degrade gracefully - doesn't matter for broadcast entertainment but not good for something safety critical. An analogue signal can be understandable almost down to the point where it disappears into the noise floor but the digital signal would have broken up to R2D2 long before.
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Yes like the switch from analogue cell phones to digital GSM, BUT that prob was only when digital voice was being rolled out. Digital voice within the same range as current VHF would not suffer drop out, instead a weak digital signal would extend the current range. 25w of radio in compressed digital mode would travel a lot further than analog VHF. Perhaps a different part of the radio spectrum might be used for a replacement short range marine voice and text comms system.
 
oceanfroggie said:
Yes like the switch from analogue cell phones to digital GSM
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Difference there, though, is that mobile phones go through a centralised system that converts between technologies. So you with your shiny new GSM phone could still call your friend who had an older analogue one, or your mum with her touchtone landline, or your granny with her Edwardian-technology rotary dial phone. Marine VHF is point-to-point, so everybody needs to be compatible, and how on earth do you manage a changeover like that?

Pete
 
oceanfroggie said:
Yes like the switch from analogue cell phones to digital GSM, BUT that prob was only when digital voice was being rolled out. Digital voice within the same range as current VHF would not suffer drop out, instead a weak digital signal would extend the current range. 25w of radio in compressed digital mode would travel a lot further than analog VHF. Perhaps a different part of the radio spectrum might be used for a replacement short range marine voice and text comms system.
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Hmmm, not convinced of this - I use both digital and analogue VHF voice comms frequently and while the digital is fine down to its threshold, if my life were to depend on a message getting through in the worst of conditions, I would be far happier knowing that I was using analogue communications - a skilled operator at the far end stands a much better chance of digging the critical information out of the hiss than they would with a digital modulation. You see it on your satellite TV as well - watch Sky during a storm the picture and sound are perfect until the losses become too great - then the screen completely freezes. With the old analogue satellite broadcasts, the picture and sound would simply get more noisy but you could make sense of it right down into the noise floor.
 
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