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Old 13-11-2011, 05:47   #46
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Re: DSC Position Request from Handheld with Boat's MMSI

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Under some strange atmospheric conditions I have listened to VHF conversations near Cape Hatteras from Long Island in the Bahamas, but I wouldn't count on that being a regular occurrence.
Probably tropospheric ducting or sporadic E-layer propagation. Both types of propagation can cause long distance VHF communication. I have an AIS monitoring station in my shop that is on 24/7 and I routinely (almost daily) receive signals from several hundred miles away at certain times of the day. Usually between midnight and 9-10am. Tropo ducting is primarily caused by temperature inversion layers in the atmosphere.

Eric
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Old 13-11-2011, 12:12   #47
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Re: DSC Position Request from Handheld with Boat's MMSI

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I'm disappointed to hear that the alert will not be relayed and will be digging in to understand that situation. Unfortunately, there is no way to test distress alerts that are not official distress alerts, so some things could be tested if that was allowed, but currently there is no provision to do that other than DSC Test.
If you think about it , there's a very simple reason , why automated distress relaying cannot be done. There is in practice no easy way to prevent a uncontrolled massive relaying that could result in thousands of alerts being generated , and being received by possible many countries land stations, all of which would have to respond. Theoretically the relaying could go round the world or large parts of it. Think of a relay starting in France and ending somewhere in Turkey, generating the need for 10000s of acknowledgements and alerting the rescue services of 10 nations.!!!

Dave
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Old 13-11-2011, 12:25   #48
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Re: DSC Position Request from Handheld with Boat's MMSI

Fairbank, just to correct your post on Sailnet

The ITU regulations state that an MMSI is assigned to the ship not the radio. Hence all radios onboard are programmed with the same number. That is the default situation.

However the ITU has recognised both becuase of AIS sarts and the proposed Class H DSC handheld, that there is a need to deal with the situation.

Some countries have forged ahead and implemented solutions. The UK has brought out along the standard ships license a portable ships license, you can have as many portable ships licenses as handhelds and each gets its own MMSI. You CANNOT use these handheld outside the territorial waters of the UK ( In this regard its like the US only BoatUS MMSI)

NOTE. If you do not have a portable ships license, Then you ARE required to confirm to the ITU standard, which is one MMSI per ship in all radios.

This is the case for FCC obtained MMSIs in the US.

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Old 13-11-2011, 15:37   #49
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Re: DSC Position Request from Handheld with Boat's MMSI

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NOTE. If you do not have a portable ships license, Then you ARE required to confirm to the ITU standard, which is one MMSI per ship in all radios.
That only applies to FCC issued MMSI's. If you have an MMSI issued by Sea Tow or Boat US and only operate domestically, you can get a different number for your handheld from them without having a portable license.

Eric
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Old 13-11-2011, 18:33   #50
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I did make that clear eric

Dave
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Old 13-11-2011, 21:03   #51
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Originally Posted by Seahunter

There probably a lot of things you've never heard of, and many more that you'd not believe. Documentation, how about the USCG? However, you'll need to watch this:
VHF Marine Radio - DSC Radio USCG- Pt. 1
+
VHF Marine Radio - DSC Radio USCG- Pt. 2
+
VHF Marine Radio - DSC Radio USCG- Pt. 3

Thanks. Didn't know that
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Old 14-11-2011, 04:27   #52
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Re: DSC Position Request from Handheld with Boat's MMSI

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Thanks. Didn't know that
Didn't know what? That your DSC radio automatically relays distress alerts as pointed out in the video? It is totally incorrect. The video is full of misinformation.

Eric
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Old 14-11-2011, 06:08   #53
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Originally Posted by fairbank56

Didn't know what? That your DSC radio automatically relays distress alerts as pointed out in the video? It is totally incorrect. The video is full of misinformation.

Eric
Yes i read further and figured that out. Just didn't see a point in reposting.
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Old 14-11-2011, 11:12   #54
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Re: DSC Position Request from Handheld with Boat's MMSI

It won't go far....the reason they make it float is not that you'll transmit from that position but that you can find it in the water if it comes off your belt or PFD. It flashes, too when in the water!


Hold it as high as you can to transmit (within circumstances of course).
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Old 15-11-2011, 08:51   #55
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Re: DSC Position Request from Handheld with Boat's MMSI

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I do believe you went on about automated DSC relay, A function that doesn't exist and never has.
Never say never. That function did in fact exist on early DSC equipment. The Sub-Committee on Radiocommunications and Search and Rescue (COMSAR), at its second session (27 to 31 January 1997), requested manufacturer's and ship captains to disable immediately, the automatic relay features of shipborne DSC equipment and to advise users of such equipment to immediately cease transmitting this type of distress alert relay. Of course, our class D units have never had the ability to this.

Eric
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Old 15-11-2011, 16:01   #56
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That's not strictly the case. What existed on HF sets was an automated repeated sending of distress relay alerts should the first one go unacknowledged. ( ie rather like the original DSC alert ) some early HF sets with DSC had a feature whereby the initial distress relay was semiautomatic. Ie no data entry but operator initiated. Subsequent distress relays were completely automatic until a distress relay ack was sent. This feature was removed ( I think ITU M.R.493-9)

It was never included into any VHF sets to my knowledge

Dave
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Old 16-11-2011, 04:36   #57
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Re: DSC Position Request from Handheld with Boat's MMSI

The information from the IMO COMSAR document states: "Automatic: A DSC radio receiving alert, transmits a DSC distress relay signal if the alert has not been acknowledged within five minutes, or if a second alert from the distress ship is received. No action by a radio operator is necessary. Only certain GMDSS DSC radios have this feature".

"Semiautomatic: An operator receiving an unacknowledged distress alert on DSC, presses a button which transmits a DSC distress relay signal. The MMSI and position of the distressed ship is automatically derived from the received distress alert, but can also be manually entered by the operator. All GMDSS DSC radios have this feature."


Nothing in the document as to whether these radio's were VHF or MF. Most likely refering to MF only.

Eric
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Old 16-11-2011, 10:57   #58
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Re: DSC Position Request from Handheld with Boat's MMSI

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The information from the IMO COMSAR document states: "Automatic: A DSC radio receiving alert, transmits a DSC distress relay signal if the alert has not been acknowledged within five minutes, or if a second alert from the distress ship is received. No action by a radio operator is necessary. Only certain GMDSS DSC radios have this feature".
I know what COMSAR says, but to my knowledge, under ITU regs no such radios ever were on the market. Im a marine radio instructor since for a long time and never seen such units. To my knowledge here in Europe under RTTE regs no such radios were legal.

Its worth pointing out that in the early days, there was several manufacturers that produced odd "outside the spec" radios, usually with incorrect software. |Early ICOMs for leisure units had for example, a Distress Acknowledge feature.

Its irrelevant anyway.

Dave
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Old 19-02-2012, 19:52   #59
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Re: DSC Position Request from Handheld with Boat's MMSI

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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
yea, no. that's pretty much how its supposed to work. It can function like a VHF PLB, great safety device as well as sweet radio/GPS. I've had my HX851 for a few months and like it a lot. I just need a cable to use the NMEA outputs into my pc > I saw a tutorial but can't find it now does anyone have a link?

Look, even the USCG is doing DSC now...
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Old 20-02-2012, 06:43   #60
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Re: DSC Position Request from Handheld with Boat's MMSI

No, that's not how it works. The guy in the CG video doesn't have a clue.

Eric
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