DSC (Digital Selective Calling) Explanation

[ka4wja]

Salty,
You are WAY over-thinking this...

(DSC is not a complex system.....to the contrary, many "tech geeks" eschew its simplicity, because of more modern digital protocols, but the fact remains that few, if any, of these more modern digital protocols are as reliable / robust as the HF-DSC system...)

I'm not sue how to explain things better, without confusing everyone!
But, I will clarify what I wrote, and I think it will be clear...
I hope!

Originally Posted by SaltyMonkey

text messages...

How do people normally perform this efficiently? What is the common software and hardware? Is there a means to convert DSC => SMS so you can contact others via phone?

and are there any limitations on character length?

for example.

First and foremost, I wrote that Maritime DSC is "sort of like 'text messaging' ", NOT that it is "text messaging"...

Originally Posted by ka4wja

a) DSC (whether VHF-DSC or MF/HF-DSC) is sort of like "text messaging", except it doesn't use any external infrastructure (no mobile phone towers, nor internet needed!), just your radio and anyone else's DSC radio...

It has absolutely NO connection to any "phone", nor any "mobile device", nor "computer", nor "tablet", nor "Wi-Fi", nor "internet", nor "SMS", etc. etc. etc. etc....
none at all!

Maritime DSC has been with us a lot longer than mobile phone "text messaging"....(remember DSC has been around for 20 years...)
And, has nothing at all to do with "text messaging", except that instead of a "voice call" over the radio, it is a 'text call" over the radio....

As for "limitations", if you look at what I wrote, it should be clear that the limitations are just these 5 messages....and that is it!!! (yes, when sending a "Distress" alert message, there is place where you can select "type of distress" (from a short list of half-dozen choices), should you choose...but that is it)
{of course, included with all messages are your MMSI# and your position, but other than that, the "message content" is just these 5 choices}

Please note the red bold type here....
These are the exact messages that can be sent, and that is it!!

Originally Posted by ka4wja

d) These DSC "text" messages are limited to just 5 simple messages...
1 --- A "test" message (just confirming that your radio's DSC systems are working).

2 --- A "routine" message (just as it sounds, this is just a friendly, routine greeting)

3 --- A "Safety" message ("Sécurité")

4 --- An "Urgency" message ("Pan Pan")

5 --- A "Distress" message ("Mayday")

Again, I'm not sure how to make it any more clear, these are the 5 messages that can be sent...





As for your other questions....here are the specific answers in red...

Originally Posted by SaltyMonkey

How do people normally perform this efficiently?
By using their DSC radios, of course...

For short-range comms, they would use their Marine VHF-DSC-FM radio....which every sailor should have had installed for at least the past decade or more!! (except for some in Australia, where some sailors have commented that the chandleries have only started stocking VHF-DSC radios in the past half-dozen years???)

For long-range comms, they would use their MF/HF-DSC-SSB Radiotelephone (usually an Icom M-802 or M-801e)....


What is the common software and hardware?
All you need is the radio....that is it!!
There is nothing else needed....


Is there a means to convert DSC => SMS so you can contact others via phone?
No...

and are there any limitations on character length?
The limitations are as stated above....
In brief, there are only 5 messages that can be sent....and that is it...
{included in each of these is, of course, your MMSI# and (assuming you've installed the radio correctly and have it connected to a GPS), your position...}

Again, I'm sorry that wasn't more clear in the videos....but since you don't see a phone, etc., nor hear any mention of a phone, etc., and the entire system is all about marine radio, I thought it was understood that this had nothing at all to do with phones...


Fair winds...

John

[ka4wja]

Ping,
While I appreciate delving into the minutia, as well as the geeky stuff...
I'd really like to keep this thread about how simple it is for the average sailor to understand and use DSC...

Originally Posted by El Pinguino

How did telex ever get involved with GMDSS ? from the link ...

Not delve into the bowels of the GMDSS standards...


fair winds...

John

[ka4wja]

Pete,
The simple answer is:
The DSC system architecture / DSC digital communications system has a lower C/N threshold, than a wideband FM voice system...

Originally Posted by Pete O Static

How does sending a digital hail on channel 70 ( DSC ) have more range than a voice message on channel 16?

This means that the DSC data will get thru at a slightly longer range than the voice signal would be able to...
{in hindsight, I should not have written any range numbers without directing you to a discussion about VHF radio range and radiowave propagation...
http://www.cruisersforum.com/forums/...ge-149499.html
sorry about that..}

And, secondarily, the DSC data is sent repeatedly....in one push of the send button, the message is sent multiple times in one transmission, and the receiving station only needs one to be decoded...

And, of course, there is FEC..."forward error correction", where the DSC signal is encoded so that the receiving station can correct errors...


I hope this clarifies...

Fair winds...

John

[Dockhead]

Originally Posted by ka4wja

. . .
Again, I'm sorry that wasn't more clear in the videos....but since you don't see a phone, etc., nor hear any mention of a phone, etc., and the entire system is all about marine radio, I thought it was understood that this had nothing at all to do with phones...


Fair winds...

John

For text messaging, the killer app is DeLorme or Yellow Brick satellite messengers. Completely interoperable with the worldwide mobile telephone network -- so can send and receive SMS messages, and can also send short text emails. The device is cheap and simple, and there are UNLIMITED plans at affordable prices.

I love radios (Extra Class ham), and have never liked anythings satellite much, but I have to say, this is a complete game-changer. Probably 90% of what you need to say on a sat phone or on HF radio can be successfully communicated by SMS.

It would be really cool to have a PSK31 to SMS bridge, which could be set up with just a few nodes, and which would be so much in the spirit of amateur radio, but I'm afraid -- no one will bother considering the existence of these devices.

[SaltyMonkey]

@john

Im having to overexplain my questions here

How do people do this efficiently, meaning how do they ENTER text transmissions easily in #2 without any complex radio keypad character shift crap that is built into the radio? What other hardware or software will make this easier? What do YOU use?

What is the character limitation, meaning are there any character limitations to send #2 like messages. Can a messages be 4096 bytes? 1 Gig? What?

Think about how people use this everyday, how do YOU use this? Is there any HAM hw or sw?

[SaltyMonkey]

with respect to DSC => SMS, it would be nice to have a sea to land bridge to translate these into phone messages.

[Dockhead]

Originally Posted by SaltyMonkey

@john

Im having to overexplain my questions here

How do people do this efficiently, meaning how do they ENTER text transmissions easily in #2 without any complex radio keypad character shift crap that is built into the radio? What other hardware or software will make this easier? What do YOU use?

What is the character limitation, meaning are there any character limitations to send #2 like messages. Can a messages be 4096 bytes? 1 Gig? What?

Think about how people use this everyday, how do YOU use this? Is there any HAM hw or sw?

What John was trying to say is that you cannot send any kind of message of your own via DSC of any kind.

DSC sends a digital message (to a specified MMSI, a list of specified MMSIs, to All Ships, or to All Ships in a specified region) which contains:

1. Nature of the call (Test, Routine, Safety, Urgency, or Mayday).

2. Nature of distress (if Distress call) (10 predefined types of distress)

3. Vessel MMSI

4. Vessel position

5. Requested working channel.


You don't get to write anything. Any further actual communication is done by phone (voice).


DSC can do a few other things:

1. Request position from specified MMSI or list of MMSI numbers.
2. Automatically respond to a position request.
3. Initiate a position report to a specified MMSI or group of MMSI

Those are the basics; there are different classes of DSC and some variations.

[nigel1]

Salty,

You cannot enter text into a DSC call. All the DSC "texts" are pre-programmed, and in fact DSC is really only an alerting system.
For example, if I want to make a routine voice call to another boat, and I know their MMSI number, I can send a Routine DSC alert to that MMSI address, and that should cause the receiving radio to sound an alarm.
An option of the DSC alert is the user can select a working VHF channel, and and depending on how the receiving radio is set up, it may automatically change to that channel.
The whole point of VHF DSC is to avoid calls being made on Ch 16, which should be exclusively used for distress and other safety traffic.

I use the routine DSC function to call the UK Coastguard when filing a traffic report.
The DSC alert is sent, and when the CG sends back the acknowledgement, my radio is automatically switched to the working channel that they have selected for the voice message to be sent.
I then just pick up the handset and pass the message, and Ch 16 is not used at all in the exchange.

[kerrydeare]

Originally Posted by nigel1

... I use the routine DSC function to call the UK Coastguard when filing a traffic report. The DSC alert is sent, and when the CG sends back the acknowledgement, my radio is automatically switched to the working channel ...

I have entered several local USCG MMSI numbers into my HX870 handheld. It is "legal" to contact the USCG in this fashion to make a system test call?

[SaltyMonkey]

Originally Posted by Dockhead

You don't get to write anything. Any further actual communication is done by phone (voice).

I must have misread then. I didn't get what he indicated above with:

"inquiring about dinner plans"

[Dockhead]

Originally Posted by SaltyMonkey

I must have misread then. I didn't get what he indicated above with:

"inquiring about dinner plans"

Yes -- he meant initiate the call as a routine call, then discussing dinner by voice on the requested working channel. As Nigel said, all without ever cluttering up 16

[nigel1]

Originally Posted by kerrydeare

I have entered several local USCG MMSI numbers into my HX870 handheld. It is "legal" to contact the USCG in this fashion to make a system test call?

It would appear that the USCG have an exclusive MMSI number to allow a VHF DSC test call to be made and acknowledged.

http://www.navcen.uscg.gov/?pageName=DSCTesting

[kerrydeare]

Originally Posted by nigel1

It would appear that the USCG have an exclusive MMSI number to allow a VHF DSC test call to be made and acknowledged.

http://www.navcen.uscg.gov/?pageName=DSCTesting

Thanks for this. I earlier encountered this particular USCG MMSI where it was listed as "USCG Coast Stations" with no reference to using the DSC
Test Call function. Very helpful.

[El Pinguino]

Originally Posted by ka4wja

Ping,
While I appreciate delving into the minutia, as well as the geeky stuff...
I'd really like to keep this thread about how simple it is for the average sailor to understand and use DSC...
Not delve into the bowels of the GMDSS standards...


fair winds...

John

John, it was a rhetorical question...the answer, of course, is that GMDSS - including the DSC component - was designed by a committee , probably the same people that brought us the giraffe and the pelican.

If it was truly was a simple system it would be possible to explain on the back of an envelope in under 5 minutes ...

In fact, if we only talk about the 'distress' sending component of the system that is quite achievable.

[Rustic Charm]

Thanks John, your explanations are very clear and simple.

I've not really found DSC hard to understand. But I am surprised here in the south how little it has taken off. It's still relatively 'new' here only 'actively' being sold in shops here in the past few years. I mean 'actively' in that a salesman said to me when asking for a VHF with DSC 'don't worry about that, it's more an American thing and you will need an MMSI to use it'. Of course I wanted DSC so I purchased a standard horizon on the Internet instead.

To date, I've not been able to raise any merchant ship using DSC in this area. This summer I'm hoping to find someone I know has DSC to test it. But, so far no one I have asked even has it.

However, there is something good happening. Finally the positives of the system are getting through and now when you go into a shop most radio's are sold with DSC than without. This is a noticed change in only the past 2-3 years I think.