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Old 10-11-2011, 22:42   #1
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DSC Position Request from Handheld with Boat's MMSI

I'm looking at buying a hand held VHF with GPS capability. The advice given by the FCC is that they should be programmed with the same MMSI as the primary radio, unless they are to be used often on other boats. Under normal circumstances I would want the hand held to have the same MMSI as the primary, since I want it to be the backup in case of a failure of the primary. I would also like to use it on the dinghy. My question is what will happen if I send out a position request from the primary radio to the MMSI number that is programmed into the unit. Will the primary radio report its own position or will the hand held respond with its position? I can see that since reception is inhibited during transmission that if the primary radio just blindly sends out the request for a position from the inputed MMSI number the primary will never receive the request and the response will be from the hand held. However if the primary recognizes its own MMSI it may never send out the position request and simply report its own position. My experience is that marine electronics are not overly smart and it will probably just transmit the position request. I figure that someone on this forum must have tried this by now. So has anyone tried this and what was the result?
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Old 11-11-2011, 00:23   #2
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Re: DSC Position Request from Handheld with Boat's MMSI

I would ask for a separate MMSI number in any case. What is the down side? None, that I can think of.
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Old 11-11-2011, 02:49   #3
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Re: DSC Position Request from Handheld with Boat's MMSI

If both have the same MMSI, Both radios will respond with their own position. ( assuming the handheld has a GPS)

In Europe, its currently impossible to seek additional MMSIs for a ships station, but the situation of DSC equipped handhelds ( a situation not envisaged under GMDSS) is currently being discussed.The UK I believe. almost uniquely in the EU has agreed to issue a Ships Portable License, hence providing an individual MMSI for a handheld. The gotcha, is that you cant use that MMSI outside the territorial waters of the UK.



The overall concern is the MMSI number space could easily be exceeded.

I beleive the situation is the same in the US for FCC MMSI authorisations( As opposed to Boat-US).

A proposal here to deal with it is http://www.gmdssforum.net/index.php?...action=search2

Dave
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Old 11-11-2011, 03:29   #4
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Re: DSC Position Request from Handheld with Boat's MMSI

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Originally Posted by goboatingnow View Post
The UK I believe. almost uniquely in the EU has agreed to issue a Ships Portable License, hence providing an individual MMSI for a handheld. The gotcha, is that you cant use that MMSI outside the territorial waters of the UK.
This is great stuff and IMHO the right way to deal with it -- Ship's Portable License.

You "can't use that MMSI outside the . . . UK", but as we all know, in a distress situation, one is relieved of such restrictions. Also, I can't really imagine that anyone will care about your using your perfectly legal in the UK portable MMSI for private communications (position polling, for example).
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Old 11-11-2011, 04:17   #5
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Re: DSC Position Request from Handheld with Boat's MMSI

sounds like a good safety option. Would you use it for ship to ship (yacht to dingy etc) as well as a backup as well as liferaft grab bag? I guess its a good safety feature to have a gps transmiting on DSC in a liferaft. What models are you looking at? I Was going to buy a $150 handheld but I like the idea of a backup radio/dsc/gps. And yes as I understand it all radios/gps etc should have the same MMSI on the ship theyre registered to
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Old 11-11-2011, 04:50   #6
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Re: DSC Position Request from Handheld with Boat's MMSI

I tested that scenario several times today. My Standard Horizon HX851 handheld has the same MMSI programed as the SH GX2000 fixed mount. Position reports, position requests, individual calls all work as expected. One calls and the other answers. The GX2000 also sends the position to my Lowrance HDS chartplotter.

Great MOB solution from my perspective.
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Old 11-11-2011, 05:00   #7
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Re: DSC Position Request from Handheld with Boat's MMSI

Dave,
Haave you actually tried it and got that result or did you find the information somewhere. If you have a source for the information I'm sure that it has additional useful information on DSC that I would like to read so could you please pass that on.

I'm currently looking at a Standard Horizon HX851.
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Old 11-11-2011, 05:01   #8
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Re: DSC Position Request from Handheld with Boat's MMSI

I agree with both of you -- great to be able to poll your dinghy, for example, for a position. Initiate ship-to-dinghy calls. Great MOB device. And you have DSC distress in the dinghy if you need it, or on your person.

I ordered a SH HX851S for these exact purposes. I will get a Ship's Portable Licence with individual MMSI from Ofcom when the radio arrives.
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Old 11-11-2011, 05:21   #9
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Re: DSC Position Request from Handheld with Boat's MMSI

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Originally Posted by Dockhead View Post
I agree with both of you -- great to be able to poll your dinghy, for example, for a position. Initiate ship-to-dinghy calls. Great MOB device. And you have DSC distress in the dinghy if you need it, or on your person.

I ordered a SH HX851S for these exact purposes. I will get a Ship's Portable Licence with individual MMSI from Ofcom when the radio arrives.
I think one big advantage is the fact that if you get caught out later than expected in a strange area you could find the bearing and distance to the boat from the dinghy. It might even help you find your boat in a crowded anchorage. The biggest problem with choosing whether to get a separate MMSI for the portable is that it is a major problem if you change your mind. Once you put in an MMSI the unit must be returned to the company to get it changed and that is not always practical. I can somewhat see why it should be difficult to change the MMSI, but it seems to me that having to ship it back to the factory is a bit too much. Seems like another case of bureaucracyrun amuck.
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Old 11-11-2011, 06:05   #10
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Re: DSC Position Request from Handheld with Boat's MMSI

The answer is "polling". You can add or delete other mmsi's from the polling group (that you create) on both radios. Depending on the model of radio they can be polled together with the same mmsi, but generally it's better to have a separate mmsi for the hand held if the purpose is ship to shore communications (EG). If the hand held is ultimately going to end up in the ditch bag, it should have the same mmsi as the ship,and ship's radio so as to communicate a ship wide pan or sos. That said exactly how far can a hand held VHF transmit if you're in the water?
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Old 11-11-2011, 06:17   #11
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Re: DSC Position Request from Handheld with Boat's MMSI

The hand held will transmit as far as it ever does from the surface of the water. The reception distance will totally depend on the height of the receiving antenna rather that the receiving antenna and the transmitting antenna.
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Old 11-11-2011, 08:51   #12
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Re: DSC Position Request from Handheld with Boat's MMSI

Though I do nopt yet have a DSC capable hand held to test , I have just tested my Standard Horizon Matrix 3000 doing a poition request from own MMSI. The radio reports no reply after about 30 seconds. It does not report its own position.
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Old 11-11-2011, 14:15   #13
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Re: DSC Position Request from Handheld with Boat's MMSI

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The hand held will transmit as far as it ever does from the surface of the water. The reception distance will totally depend on the height of the receiving antenna rather that the receiving antenna and the transmitting antenna.
It's good to see you remember your USCG course material, however, VHF is only line of sight. With DSC, the signal repeats itself through other DSC radios in the area until it connects to somebody who actually cares (USCG). This is why it's important to have your DSC-VHF radio turned on at all times (when at sea) as you won't know that you've been used as a repeater. Anyways, as for your position request, it probably went into etherland if you don't have it connected to your gps chartplotter. Another thing the radio needs to be set up (it doesn't come ready to go) see: page 52 in your manual and the vessel has to be in the polling list.
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Old 11-11-2011, 14:41   #14
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Re: DSC Position Request from Handheld with Boat's MMSI

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Originally Posted by Seahunter View Post
With DSC, the signal repeats itself through other DSC radios in the area until it connects to somebody who actually cares (USCG). This is why it's important to have your DSC-VHF radio turned on at all times (when at sea) as you won't know that you've been used as a repeater.
Iv'e never heard of this and frankly, don't believe it for a second. Do you have any documented proof of this function?

Eric
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Old 11-11-2011, 14:45   #15
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Re: DSC Position Request from Handheld with Boat's MMSI

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Originally Posted by goboatingnow View Post
If both have the same MMSI, Both radios will respond with their own position.
The radio sending the request won't respond as it won't receive the position request because it can't receive while sending.

Eric
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