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Old 01-05-2013, 17:16   #1
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Dumb DSC VHF questions

Hi all,

I'm thinking of finally upgrading the antique (non-DSC) VHF aboard. I've read how the distress function works by sending an all stations DSC message with the ship's MMSI and GPS location (if supplied) and I understand the safety benefit of this. I also think I get the gist of how a ship to ship DSC call works using an MMSI number.

My dumb questions: Does a DSC VHF send a digital signal (i.e. MMSI number) at any other time? Is there a way to identify the origin of a standard, analog radio call because the sender is using a DSC radio?

Thanks much,
Gary
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Old 01-05-2013, 18:00   #2
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Re: Dumb DSC VHF questions

The DSC VHF radios don't generally transmit their MMSI or GPS data, but there is a "query" capability, where (if I am not mistaken) your radio can be interrogated for your position. I believe this works by the interrogating station sending a specific DSC message that includes your MMSI. This way your radio is the only one that responds.

I may be wrong on the details, so look into this if it concerns you.
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Old 02-05-2013, 07:28   #3
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Re: Dumb DSC VHF questions

Your radio will only respond to a position query if you have it set to auto-reply. The default for this setting is typically "OFF". The only way another boat can get your position is if you have auto-reply "ON", or you respond manually. The other boat would have to know your MMSI in order to query for your position as well.

Eric
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Old 01-12-2013, 15:35   #4
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Another dumb question: In the US we have to set all VHF radios on board to the same MMSI. If a MOB with handheld issues distress call will the other VHF radios on board recognize the distress call even though they have the same MMSI as the distress message?
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Old 01-12-2013, 17:30   #5
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Re: Dumb DSC VHF questions

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Originally Posted by transmitterdan View Post
Another dumb question: In the US we have to set all VHF radios on board to the same MMSI. If a MOB with handheld issues distress call will the other VHF radios on board recognize the distress call even though they have the same MMSI as the distress message?
I suspect they will. Our hand held DSC VHFs are programmed with the same MMSI as our fixed radio. A DCS call on one shows up on the other. We take advantage of this - when I am out in the dinghy with the HH, Michele can simply poll my position on the fixed radio and it shows up on the chartplotter. Vice-versa, if my dinghy excursion was a rum squall and I don't remember where the boat is, I can poll its position and use the HH to navigate back to it!

Also, regular calls to/from our HH from/to our fixed radio work just fine.

The only thing we have found the radios share is the DSC phone call feature from other boats. If someone calls us, all radios ring and any can answer.

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Old 01-12-2013, 18:08   #6
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Re: Dumb DSC VHF questions

Do people actually use the DSC function? I've never called anyone, never had anyone call me, and don't know anyone who's had it happen either. I've had a DSC radio for years, broadcast AIS, etc. Everyone just hails on 13 or 16.
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Old 01-12-2013, 18:16   #7
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Re: Dumb DSC VHF questions

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Originally Posted by rebel heart View Post
Do people actually use the DSC function? I've never called anyone, never had anyone call me, and don't know anyone who's had it happen either. I've had a DSC radio for years, broadcast AIS, etc. Everyone just hails on 13 or 16.
I tried calling a pushboat in the ICW.......new SH GX2150.......it didn't work, they didn't know what was happening nor how to answer. But when I hailed them by name on 13 the called right back.
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Old 01-12-2013, 18:20   #8
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Re: Dumb DSC VHF questions

Oh man, we live on it. Never have to listen all day to the mindless chatter on the cruiser hailing channel. Or the endless radio checks, etc. Anyone we really want to talk to has our mmsi. Everyone else can dinghy up and say hi if they want to talk to us.

Other than "phone calls", we use it all the time to locate each other or to push waypoints back to the boat from the dinghy when exploring possible cuts and anchorages.

Best thing since sliced bread. The problem is most radios do not implement it well. Standard Horizon makes it so simple. Icom is like Sanskrit.

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Old 01-12-2013, 18:44   #9
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Re: Dumb DSC VHF questions

We recently completed the Sail Indonesia Rally and I introduced quite a few very-experienced cruisers to DSC calling, many of whom wondered why they had never used it before. It allows a call to be made to a specific MMSI number privately (although the conversation is not). This would be handy if you wanted to invite one boat in the anchorage over for cocktails but didn't want to hurt the feelings of the boats you didn't invite (it didn't help much, though, as everyone would see where the dinghies wound up for the evening).

More importantly, it freed up the hailing channels, which many Indonesians also use for conversations, making obscene noises and even playing the AM radio over.

The drawback is that if you have multiple radios sharing the same MMSI number, all radios will 'ring' on an incoming DSC call and will continue to ring until the call is answered on every single radio that's ringing, unlike a phone at home where a call answered at one extension silences all others. Regardless, we remain big fans of the feature.

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Old 01-12-2013, 18:52   #10
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Re: Dumb DSC VHF questions

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The drawback is that if you have multiple radios sharing the same MMSI number, all radios will 'ring' on an incoming DSC call and will continue to ring until the call is answered on every single radio that's ringing, unlike a phone at home where a call answered at one extension silences all others.
Hmmm, I can't say this is true or not for us. It seems like that is not the case, but we have our radios set to only ring 5 times and then go silent. From memory, I recall that once answered by one radio, the other radios go to the designated channel and become a party line for the answering radio connection. They are set on auto answer, so maybe that is why. Or maybe different manufacturers implement it differently.

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Old 02-12-2013, 05:07   #11
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Re: Dumb DSC VHF questions

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Originally Posted by rebel heart View Post
Do people actually use the DSC function? I've never called anyone, never had anyone call me, and don't know anyone who's had it happen either. I've had a DSC radio for years, broadcast AIS, etc. Everyone just hails on 13 or 16.

Very underutilised for general calling even here in Europe , where its been in use for seem time.


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Old 02-12-2013, 05:21   #12
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Re: Dumb DSC VHF questions

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if my dinghy excursion was a rum squall and I don't remember where the boat is, I can poll its position and use the HH to navigate back to it!
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Old 03-12-2013, 00:01   #13
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Re: Dumb DSC VHF questions

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Does a DSC VHF send a digital signal (i.e. MMSI number) at any other time?
When you have a AIS transmitter, you will send out your MMSi.
Then the boats in vicinity can see your MMSI on their plotter
and can call you up when there is a reason.
Greetings, Wilhelm
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Old 03-12-2013, 00:09   #14
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Quote:
Originally Posted by rebel heart View Post
Do people actually use the DSC function? I've never called anyone, never had anyone call me, and don't know anyone who's had it happen either. I've had a DSC radio for years, broadcast AIS, etc. Everyone just hails on 13 or 16.
We use it all the time!--especially between the dinghy and mothership. The drone of Ch. 16 can get drowned out by our stereo, or completely missed during a nap. But that DSC alarm cuts through unmistakably.
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Old 03-12-2013, 00:12   #15
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Re: Dumb DSC VHF questions

Quote:
Originally Posted by Paul Elliott View Post
The DSC VHF radios don't generally transmit their MMSI or GPS data, but there is a "query" capability, where (if I am not mistaken) your radio can be interrogated for your position. I believe this works by the interrogating station sending a specific DSC message that includes your MMSI. This way your radio is the only one that responds.

I may be wrong on the details, so look into this if it concerns you.
You are not wrong on the details. See: VHF-DSC Marine Radio Technical Information - Understanding DSC VHF Marine Radios

DSC basically gives you these functions:

1. Distress call. Will transmit a generic or specific distress call including your position and MMSI. Radios within range on other vessels will all shriek. Coast guard acknowledges and calls you back. Much more efficient than simple voice distress call.

2. Position polling. Request position of another vessel, if you know its MMSI, and if the other vessel has set its radio to respond to position requests. Position will be shown on your chart plotter if it is connected.

3. Position report. You can broadcast your position to selected vessels.

4. Routine DSC call. I am amazed that this is so little used -- it is incredibly convenient. If you enter a vessel's MMSI number, you can call so that their radio rings like a telephone and automatically switches to your working channel. This is how I always call the Coast Guard for radio checks or filing passage plans.


With a DSC handheld on your dinghy, you can check position of the dinghy from the mother ship, and vice versa.

DSC is awesome.
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