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Author Topic:   Datagrams on Data Links from Digital Selective Calling Radios
jimh posted 04-21-2014 04:59 PM ET (US)   Profile for jimh   Send Email to jimh  
I have created a separate article that presents the information I have deduced about the content of some datagrams sent over the IEC-61162 data link interface from a Class-D digital selective calling radio to other vessel electronic devices. See

jimh posted 04-24-2014 02:37 PM ET (US)     Profile for jimh  Send Email to jimh     
I am also interested in discovering when a digital selective calling radio will output a datagram on its data link using IEC-61162. So far I have seen only a few instances when this occurs:

--when a DSC radio receives position a position report from another station in response to a position request

--when a DSC radio receives a distress alert message from other station

I am testing for more situation when there will be output of a datagram on the data link from the radio, and I will append more findings to this thread.

jimh posted 04-24-2014 06:18 PM ET (US)     Profile for jimh  Send Email to jimh     
More testing showed this behavior:

If a DSC radio was sent an unsolicited position report from another station, that is, the position report was not a reply to a position request, then the radio did not output a datagram on its data link interface.

jimh posted 04-26-2014 03:00 PM ET (US)     Profile for jimh  Send Email to jimh     
I believe I have been able to interpret the datagram that is sent on the data link output of a DSC radio to other ship electronic equipment when that DSC radio receives a distress alert message from another station and sends datagram according to IEC-61162. I explain in detail in the linked article (above).
Chuck Tribolet posted 04-27-2014 07:30 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I suspect these results may not be general to all DSC VHF


jimh posted 04-28-2014 08:47 AM ET (US)     Profile for jimh  Send Email to jimh     
Chuck--What is your basis for that statement?

The results from any Class D radio should be consistent with the recommendation of the ITU-Rec. M.493-13. That recommendation cites IEC-61162 as the standard by which a data interface should be provided, which should also provide consistency.

Here is an excerpt from M.493-13:

12.6 Data interface

DSC equipment should be provided with facilities for exchange of data from shipborne navigational equipment or systems, or other shipborne equipment as necessary in accordance with IEC 61162 for purposes including automatic position updating.

Chuck Tribolet posted 04-28-2014 10:36 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
A given radio may do more than is required for Class D.


jimh posted 04-28-2014 01:10 PM ET (US)     Profile for jimh  Send Email to jimh     
Chuck--Yes, lots of them already do provide more features than required. For example, Standard-Horizon provides a built it GPS receiver, and a way to set up for automated position requests at a preset interval, and none of that is required in Class-D. But here I am looking at the datagrams that will be sent from a typical Class-D radio on its data link. I am looking at the most common datagrams--ones from distress alert messages--and I very much doubt you will find much variation in them from brand to brand, radio to radio. If you make your own observations and find something that differs from what I have described, please let me know. I am always interested in new examples of data sent on these wired data links.
jimh posted 04-29-2014 11:16 AM ET (US)     Profile for jimh  Send Email to jimh     
I added a new section to the reference article, "The Interface Between Human and Machine," discussing the several interfaces in the flow or path of a distress alert signal, beginning with a human who wants to send a signal and ending with a human that receives the signal. The interface between humans and machines and machines and machine is mostly governed by applicable standards or recommendations, but I could not find a recommendation for how a recreational grade chart plotter ought to present information about a distress alert call. I would be interested to hear from any readers who might have insight or a comment on this part in the signal flow.
Chuck Tribolet posted 04-29-2014 04:50 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
A chart plotter should do something real obvious to call attention to the incoming distress call (lots of beeping), display vessel, lat-long, distance, and bearing, and if space on the screen allows, the position on the chart. And have a "push enter to navigate there" option.


jimh posted 05-01-2014 11:32 AM ET (US)     Profile for jimh  Send Email to jimh     
A DSC radio sold in the USA is subject to some rather strict requirements on its behavior upon receiving a distress alert call. The frequency and duration of the aural alert tones are spelled out in the cited recommendations, resulting in the radio producing the aural alert signal that I call "the French police car siren."

Chart plotters sold in the USA for use on recreational boats are not under any sort of similar restraint of sale for certain behaviors related to receipt of a datagram from a DSC radio. In fact, I am not sure there is really any regulatory guidance on what datagrams a DSC radio might sent to a chart plotter. But there seems to be no regulations on what a chart plotter will do with those signals once it receives them on its IEC-61162 wired interface.

My anecdotal observations from my HDS-8 chart plotter are reported in my DSC Alert Test articles:

I plan to report more about how a chart plotter responds to a radio's signal via wire interface in a future article. In very limited testing so far, the response of the chart plotter has been a bit confusing and will be investigated further.

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