DSC Basics

[jackdale]

This site is short and sweet

VHF DSC - safety for all

[Rustic Charm]

Originally Posted by jackdale

This site is short and sweet

VHF DSC - safety for all

and looky here, Australia has it's first VHF DSC volunteer costal station commissioned..

VHF DSC for Pt Phillip Bay

[Rustic Charm]

It seems to me that the basic confusion going on is that there is a difference between VHF and HF DSC and what they are capable of.

Secondly, there is a difference in use of the DSC system in Australia and the US regions.

And this talking of 'class' of DSC is not helping laymen like me

[Dockhead]

Originally Posted by Rustic Charm

It seems to me that the basic confusion going on is that there is a difference between VHF and HF DSC and what they are capable of.

Secondly, there is a difference in use of the DSC system in Australia and the US regions.

And this talking of 'class' of DSC is not helping laymen like me

The only difference between Australia and the rest of the world is that Australia, uniquely, elected to declare no Sea Area A1 anywhere in its waters. Ordinarily all countries have a Sea Area A1 around their coasts, and GMDSS protocol calls for VHF DSC to be effective in Sea Area A1 areas for distress signalling, because SAR services are supposed to have seamless VHF coverage in Sea Area A1 areas. In Australia, uniquely, the area right up to the coast line is declared as a Sea Area A3, so the SAR services do not guarantee coverage with VHF (or for that matter, MF/HF radio), and GMDSS protocol calls for SOLAS vessels to use Inmarsat or EPIRB for distress signalling. As someone above mentioned, you are likely to be ok with MF/HF DSC in Australian waters, so in the absence of seamless VHF coverage, Australian boats are especially well advised to have SSB sets on board with DSC capabilities. This would be particularly useful for pan pan and securite calls when you find ourselfare reluctant to set off your EPIRB.

Your coast guard and SAR services certainly have DSC on their VHF radio stations, and you can certainly call your coast guard and SAR services with VHF DSC as long as you have coverage; it's just not recognized as an official GMDSS protocol because of the lack of seamless coverage -- that is, you are not allowed to rely on it.

Because of the lack of seamless VHF coverage in Australia, if you want to be sure that you can actually talk to rescue services and/or coast guard (which obviously you can't do via EPIRB), you will need a sat phone and/or SSB radio. Non-INMARSAT sat phones are not GMDSS, but for a non-SOLAS boat, this is probably not really important. Note that Australia was the first country to abandon non-DSC watchkeeping on MF/HF, so if you want to use your SSB set for distress signalling, you MUST have DSC.

The reason for all of this is the great length of deserted coastline in Australia. In other parts of the world, there are SAR and/or coast guard VHF coast stations every 30 or 40 miles and seamless coverage. You can be sure to be able to reach a coast station by VHF anywhere up to 40 or 50 miles offshore. Therefore, VHF DSC is your primary distress signalling and even SOLAS vessels are not required to have anything else. Your situation is a little different.

Here's a good article which might clear up some things: GMDSS requirements

[ka4wja]

Dockhead certainly wrote this in a much more succinct way than I would!!

But, one thing that we both left out....
(I specifically didn't want to add anything else that might confuse things....but realize I should have included this before...)

That is that while Australia did declare all of their waters Sea Area A3, they also have some Sea Area A4 waters that they are responsible for....and this is why they use HF-DSC, as well as INMARSAT-C, to cover these waters...
And, this is why Australian yachtsmen have long ago been advised to carry HF-DSC radios...
{And, while I don't have the specific reg in front of me, I recall that for many years now if a non-SOLAS Australian vessel (such as a cruising sailboat) wished to equip with a marine HF radio, they were required to equip their boat with an HF-DSC radio as well as obtain the requisite licenses/training for this....
This contrasts with the US...where we haven't had any non-DSC marine HF rigs approved / sold for a LONG time, but you as the boat owner could equip your boat with whatever marine HF radio you desired...hence why there are still so many of my fellow US-flagged cruising boats that, after about 20 years, still have old non-DSC HF rigs aboard! }




BTW, in addition to all my ramblings, THANKS...
Thanks to you Dockhead for starting this thread!!

Fair winds..

John

[jackdale]

Originally Posted by Rustic Charm

It seems to me that the basic confusion going on is that there is a difference between VHF and HF DSC and what they are capable of.

Secondly, there is a difference in use of the DSC system in Australia and the US regions.

And this talking of 'class' of DSC is not helping laymen like me

Classes of DSC - from an Australian perspective.

VHF DSC technical specification

[ve7mdl]

This is getting to be a long thread and I have been out of network range for a few days, so let me try and add a few comments:

1. Class A DSC radios are used by large ships and expensive, so this class is not used by pleasure craft. Class E is the pleasure craft version of MF/HF DSC. Class D is the one used in pleasure craft VHF radios and I think this is the focus of this thread.

2. Accepting a distress (or distress relay) alert on a Class D radio only has a local meaning. The radio does not transmit anything. Some radios allow you to ignore a distress alert (and I'll use the correct term here), which is useful if you have some important communication going on in one radio while another switches to channel 16.

3. DSC distress alerts should be followed up with a standard MAYDAY call on channel 16. This allows SAR personnel to confirm the validity of the distress call and to get further information (number of POB, description of vessel).

4. While some radios may allow users to issue distress alerts without having a GPS connected, the accuracy of the location is doubious.

5. While you should not test a DSC radio by pushing the distress button, there is a very convenient test function on all newer radios. When issued, the test call (which is sent to a specific station) will show up at the receiving station and this station can respond either manually or automatically. This way you test both the DSC transmit and receive function of the radio.

BTW, the Canadian Coast Guard supports VHF DSC at all their stations.

Cheers, ....Erik.
Industry Canada recognized Radio Instructor and Examiner
m/v B.C. Girl.

[gamayun]

Thanks, Erik. That was concise and cleared up the different radio classes for me.

I have always wondered about using the handheld VHFs with DSC. I assumed that the signal is line of sight, but with the more powerful CG towers that we have in the US (Rescue 21 system), can a handheld DSC alert get picked up at least 20 NM offshore, ignoring all other conditions such as sea state, etc.?

[hellosailor]

gamayun-
20nm can very well be "line of sight" !
I have used a 5-watt handheld VHF to communicate through an antenna that was sited on the Empire State Building, very likely 20nm away from where I was. And yes, I could still physically SEE that building, at that distance. That's what makes it line of sight.
Of course the USCG is not likely to have many antennas a thousand feet up in the air--but they still do try to erect them on rooftops and towers, way higher than the antenna on a recreational vessel.
You will find "line of sight" or "distance to horizon" calculators on the web, which will let you put in the height of two different antennas, above sea level, and they'll give you the actual "line of sight" distance between those two heights.
VHF also sometimes "skips" or "bounces" and a ten mile range between two sea level radios is easily possible when that happens. So, "your mileage may vary".

[hellosailor]

Something that I don't recall ever seeing mentioned, by anyone, is that by now we should all be anticipating the death of all current radio in favor of "the internet of things" and marine radios transitioning to use IP (internet protocol) and internet addresses, now plentiful since IP addresses have expanded from four triplets to eight.


Really, in an age when refrigerators and vending machines have their own IP addresses, and the telephone network has been eclipsed by radios using IP addresses and VOIP (we mistakenly call them cell phones), why shouldn't marine radio systems by simplified and improved by jumping over to the internet?


If my personally assigned IP address (yes, anyone can get them) was 555.121.255.512.125.551.212.555 and I had a range with 50 address in it, it wouldn't matter if I was using a cell phone, or VHF, or marine HF, or satphone. The same master routers and name servers that shuffle everything around the internet now, could just as easily route all my traffic to me, regardless of the device and the location, as long as it had some type of internet access. And with satphones and all being dirt cheap these days, that's no longer unreal. Internet access from Mt. Everest and the Antarctic is something like 16 years old by now!
Logically?
MMSI, DSC, all of that is a horrible wasted redundant thing, when the systems are begging to be integrated. No more private databases to maintain at the FCC or NOAA or whoever, just point the 'call' to the internet, and let it get routed along with everything else. (Or hacked, as the case may be.)


These days, when a kid gets a cell phone, changes schools, family moves, goes to college out of town, gets a job someplace else, moves cross-country...their phone number stays the same and stays with them. It ain't the 1990's any more! Not so long ago, if you moved cross-town, you had no choice except a new number. Now? Really, you've got to be joking.


It is time the ITU took up consideration of a paradigm shift to the 'internet of things' and gave all the vendors a chance to move from beta to vhs once again.(G)

[gamayun]

Originally Posted by hellosailor

gamayun-
20nm can very well be "line of sight" !

Yeah, duh. I guess where my thinking was going is whether they're more likely to pick up the DSC "data" than a voice call on a handheld? You seem to be saying that it's all the same.

[Terra Nova]

Originally Posted by hellosailor

...we should all be anticipating the death of all current radio in favor of "the internet of things" and marine radios transitioning to use IP...with satphones and all being dirt cheap these days, that's no longer unreal...

Sat link could do it. Expensive. But remember what happened to Rebel Heart? Service cancellation notice was sent by snail mail!

[Rustic Charm]

Originally Posted by hellosailor

Something that I don't recall ever seeing mentioned, by anyone, is that by now we should all be anticipating the death of all current radio in favor of "the internet of things" and marine radios transitioning to use IP (internet protocol) and internet addresses, now plentiful since IP addresses have expanded from four triplets to eight.


Really, in an age when refrigerators and vending machines have their own IP addresses, and the telephone network has been eclipsed by radios using IP addresses and VOIP (we mistakenly call them cell phones), why shouldn't marine radio systems by simplified and improved by jumping over to the internet?


If my personally assigned IP address (yes, anyone can get them) was 555.121.255.512.125.551.212.555 and I had a range with 50 address in it, it wouldn't matter if I was using a cell phone, or VHF, or marine HF, or satphone. The same master routers and name servers that shuffle everything around the internet now, could just as easily route all my traffic to me, regardless of the device and the location, as long as it had some type of internet access. And with satphones and all being dirt cheap these days, that's no longer unreal. Internet access from Mt. Everest and the Antarctic is something like 16 years old by now!
Logically?
MMSI, DSC, all of that is a horrible wasted redundant thing, when the systems are begging to be integrated. No more private databases to maintain at the FCC or NOAA or whoever, just point the 'call' to the internet, and let it get routed along with everything else. (Or hacked, as the case may be.)


These days, when a kid gets a cell phone, changes schools, family moves, goes to college out of town, gets a job someplace else, moves cross-country...their phone number stays the same and stays with them. It ain't the 1990's any more! Not so long ago, if you moved cross-town, you had no choice except a new number. Now? Really, you've got to be joking.


It is time the ITU took up consideration of a paradigm shift to the 'internet of things' and gave all the vendors a chance to move from beta to vhs once again.(G)

I would not rely on anything to do with the internet for saving life and limb at this time. Just look at the delay in sending and receiving sms messages, the amount of times the internet connection fails, the amount of times those on NBN have phone problems.. Nope.. maybe in the future, but not yet. No where near reliable enough.

[Sandero]

Just curious... can any supply stats on how many or what percentage might be better of pleasure craft have upgraded to DSC?

Do we have any reports of how many times DSC was used in an emergency or distress situation? Is this making a difference? Saving lives? is there any way to know? It sure seems better...

Why don't they require DSC? and phase out the old VHF?

[Rustic Charm]

Originally Posted by Dockhead

The only difference between Australia and the rest of the world is that Australia, uniquely, elected to declare no Sea Area A1 anywhere in its waters. Ordinarily all countries have a Sea Area A1 around their coasts, and GMDSS protocol calls for VHF DSC to be effective in Sea Area A1 areas for distress signalling, because SAR services are supposed to have seamless VHF coverage in Sea Area A1 areas. In Australia, uniquely, the area right up to the coast line is declared as a Sea Area A3, so the SAR services do not guarantee coverage with VHF (or for that matter, MF/HF radio), and GMDSS protocol calls for SOLAS vessels to use Inmarsat or EPIRB for distress signalling. As someone above mentioned, you are likely to be ok with MF/HF DSC in Australian waters, so in the absence of seamless VHF coverage, Australian boats are especially well advised to have SSB sets on board with DSC capabilities. This would be particularly useful for pan pan and securite calls when you find ourselfare reluctant to set off your EPIRB.

Sounds good.. helped me understand that once I worked out what a Sea Area A1 is.

Your coast guard and SAR services certainly have DSC on their VHF radio stations, and you can certainly call your coast guard and SAR services with VHF DSC as long as you have coverage; it's just not recognized as an official GMDSS protocol because of the lack of seamless coverage -- that is, you are not allowed to rely on it.

This bit, I'm not so sure about From what AMSA tells us the only costal stations that will have DSC are those who have voluntarily purchased their own VHS with DSC sets? Would they not advertise their MMSI's if they had DSC?

Because of the lack of seamless VHF coverage in Australia, if you want to be sure that you can actually talk to rescue services and/or coast guard (which obviously you can't do via EPIRB), you will need a sat phone and/or SSB radio. Non-INMARSAT sat phones are not GMDSS, but for a non-SOLAS boat, this is probably not really important. Note that Australia was the first country to abandon non-DSC watchkeeping on MF/HF, so if you want to use your SSB set for distress signalling, you MUST have DSC.

Ok, I 'get' that DSC is available on SSB, but VHF?

The reason for all of this is the great length of deserted coastline in Australia. In other parts of the world, there are SAR and/or coast guard VHF coast stations every 30 or 40 miles and seamless coverage. You can be sure to be able to reach a coast station by VHF anywhere up to 40 or 50 miles offshore. Therefore, VHF DSC is your primary distress signalling and even SOLAS vessels are not required to have anything else. Your situation is a little different.

Here's a good article which might clear up some things: GMDSS requirements

Thanks Dockhead, that's both helped explain and raised more questions for me..

It still seems to me that VHF DSC is NOT well establised in Australia and if your trying to call a coast guard with DSC it will be very hit and miss.