Standard-Horizon HX890, CLASS-H DSC Radio

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
SVGrendel
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Standard-Horizon HX890, CLASS-H DSC Radio

Postby SVGrendel » Tue Dec 11, 2018 6:34 pm

[Originally part of an earlier discussion on formal recommendations for DSC radios, but now separated into its own thread--jimh]

I recently acquired a new Standard Horizon HX890 handheld described as Class H. The vendor states "...The new HX890 shares all the same capabilities of the extremely popular HX870, with the addition of some great new features...." Note that the HX870 is described as a Class D radio.
http://www.standardhorizon.com/indexVS. ... rodID=2869

I was disappointed to discover that the HX890 does not support transmitting the DSC Position Request function yet the HX870 does support this function (according to its manual). To be fair, the HX890 manual omits this (TX) function although it describes how to receive (RX) a position request from another radio. However, the HX890 manual also describes support of auto polling a "fleet" of other vessels (positions), yet my initial testing shows that the function does not work--which may be reasonable insofar that auto polling requires periodic transmission of a position request to each of the vessels in the "fleet".

It also appears that the HX890 does not support transmission of All Ships Urgency and Safety messages, while the HX870 does (again, according to the manual).

Clearly, and contrary to the product advertisement, the Class H HX890 does NOT share all the same capabilities of the Class D HX870. Upon contacting the vendor, I was advised that the differences in capabilities are due to the differences in Class. (They also advised that they may revise their advertising.)

I've found little information on the relative capabilities of VHF/DSC Class D and Class H on the internet--[the prior] thread seems to be as good as it gets (and thank you for that!). But it appears that Class H is a step backward from Class D (which is unfortunate).

I also regret that the link (in the initial thread post) to the gentleman from Australia, Glenn Dunstan, appears to be broken. I would have liked to view his information on the matter.

Finally, the "great new features" advertised for the HX890 appear to be limited to the ability to receive FM broadcast (entertainment) stations, and some new voice scrambling capabilities. Hardly a beneficial trade off for useful marine DSC functionality, IMO.

jimh
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Re: Standard-Horizon HX890, CLASS-H DSC Radio

Postby jimh » Wed Dec 12, 2018 11:31 am

SVGrendel--hello, and welcome to the forum. I noticed that Glen's website domains have apparently lapsed and been acquired by someone more interested in redirecting traffic to an on-line merchandise shopping website than to information about GMDSS topics. This is unfortunate. Having been operating this website for more than 20-years, I periodically wake up from a nightmare that I forgot to renew my domain name registration, which is perhaps the most valuable asset of the website. (I got quite anxious just talking about that, so I had to go check my domain expiration date: good for another 1.5-years before renewal. Phew.)

I also tried to search for a newer site run by Glen about GMDSS, but I could not find one. I don't know what happened or where the information went. At least some of the content is preserved here by my quotation of it. The temporary nature of some web resources is unfortunate but a continual problem.

Back to GMDSS information.

Thanks for the comments on the new Standard-Horizon HX890 handheld Class-H certified DSC radio. I will look for some more information about Class-H criteria in the associated ITU-R Rec. M-493-14 standard. I was just updating some broken links to that resource in other articles. Here is working hyperlink to that resource:

Digital selective-calling system for use in the maritime mobile service
https://www.itu.int/rec/R-REC-M.493

A very careful reading of that document should reveal more information about the distinctions between a Class-D and Class-H DSC radio. I will include such a careful reading on my to-do list, and I will remark here if I find anything of interest. Thanks for bringing up the topic.

jimh
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Re: Standard-Horizon HX890, CLASS-H DSC Radio

Postby jimh » Wed Dec 12, 2018 1:50 pm

I have browsed the ITU Recommendation R-M.493-15 searching for mention of "Class H". I found that on folio 42 in TABLE A1-4.9, under the rows "Polling" and "Polling Acknowledgement" that the Class-H device is not required to perform those DSC functions. However, neither is a Class-D device, yet most of them do perform that function.

The "call sequence" mentions "1st telecommand" should be "Symbol 103" and "2nd telecommand" should be "Symbol 126."

I interpret that as follows:

From TABLE A1-3, Symbol 103 as 1st telecommand means "Polling"
From same table, Symbol 126 as 2nd telecomand means "No information"

The details of making and acknowledging a position request are given in section 8.3.3.2. Here is an excerpt:

For position requests message 2 consists of 6 no information symbols (symbol No. 126).

In acknowledgements to a call requesting ship’s position (see Fig. 3d)) [sic] message 2 consists of twelve
digits (six symbols), the first of which should be coded in accordance with § 8.1.2 followed by one
symbol No. 126.


Section 8.1.2 describes how to send position data, but curiously only to a resolution of one whole minute.

Based on this rather cursory look, it seems that position polling and position polling request acknowledgement are not mandatory behaviors for either Class-D or Class-H DSC VHF Marine Band radios--unless I have significantly misinterpreted the recommendation.

As for Standard-Horizon not including the function to make a position poll request in their model HX-890, I can only guess the motivation. Perhaps they thought that a handheld radio would be subordinate to a ship's fixed mount radio, and would be used on an auxiliary vessel like a tender or dinghy. In that case the mothership would be polling to find out where the auxiliary vessel has gone, not the other way around. But omitting the function to make a position poll request, unless there is some regulatory reason to drop it, seems like a bad move. Maybe the dinghy is lost and wants to find the mothership.

The most curious aspect: as best I can recall, it was Standard-Horizon that introduced position polling in DSC radios, long before it was available in other makes. That they seem to have broken it in their HX890 radio is somewhat odd.

SVGrendel
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Re: Standard-Horizon HX890, CLASS-H DSC Radio

Postby SVGrendel » Fri Dec 14, 2018 2:16 am

Thank you, Jim, for your helpful insights. (And for running such a "tight ship" on your forum!)

First of all, I should commend Standard Horizon for promptly amending their website description of the HX890. They now omit the claim that it "...shares all the same capabilities of the...HX870...." and merely state that it "...has some prominent new features....", to wit: a new flavor of voice scrambler and FM broadcast reception.

I also reviewed the ITU Recommendation M.493-14 publication which I found, as a casual reader, fairly inscrutable. Nevertheless, I see that your reference to Table A1-4.9 shows that Polling and Polling Acknowledgement appears to be not only "not required" but "not allowed" (if I correctly interpret the meaning of "---" in the table; see the Legend to the Tables on p. 30). Which, if true, makes it even more curious that the function commonly appears on both Fixed and (some) Handheld Class D radios.

Based on review of on-line manuals, it appears that the Class D handhelds vary in this regard:
--The Standard Horizon HX851 and HX870 support TX of Position Request (and Position Response), as does the Uniden MHS335BT and Lowrance Link2 (which has it under some "buddy boat" rubric);
--The ICOM M93D, however, does not support Position Request, but does support Position Response (as does the Class H HX890). (Uniquely, the ICOM's GNSS receiver apparently receives GLONASS as well as GPS signals for position information.)

I also note that Table A1-4.5 appears to prohibit Class H radios from transmitting the Urgency and Safety All Ships message--which is consistent with the absence of this function on the Class H HX890 while it is present on all of the Class D handhelds.

Other tables (A1-4.3 ff) show some differences in Class D and H in the area of Distress Alert Relays and Relay Acknowledgements, but I'm ignorant of what practical difference that would make. But, as a practical matter, on more than one occasion after an evening of revelry at some shore-side pub up in the wilds of coastal British Columbia I have encountered the challenge of finding the "mothership" in a large anchorage after a fog has rolled in. I would have happily used the Position Request function of a handheld radio (and it's navigation capabilities!) to reduce the time required to tuck in for the night!

And regarding section 8.1.2, I can report that the Position Response sent by the HX890 includes (lat & lon) minutes position to 4 decimal places. I dunno how that comports with the description in 8.1.2, but I seem to recall that one of the problems of the early SC-101 DSC radios was a dilution of accuracy and precision in position data that compromised its effectiveness in finding a vessel in distress.

Altogether, is is frustrating that the sole canonical reference for the relative capabilities of various classes of VHF/DSC radios seems to be the inscrutable ITU publication above. I can only imagine the difficulties that product engineers must overcome in attempting to get their devices type-approved by various national RT authorities.

BTW, not to be picky, but wouldn't this thread be more appropriately lodged under your VHF RADIO collection rather than SMALL BOAT ELECTRICAL?

jimh
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Re: Standard-Horizon HX890, CLASS-H DSC Radio

Postby jimh » Fri Dec 14, 2018 1:47 pm

Re the ability of a DSC radio to sent an ACKNOWLEDGEMENT of a DISTRESS ALERT call: I believe that only Class A DSC radios are allowed to do this. Sending an ACK to a DISTRESS ALERT may cause the automatic repetition of the alert at periodic intervals by the originating radio to stop. You don't want a local boat with a Class-D radio to be able to shut off another boat's distress alert; only a rescue agency with a shore station should do that.

Re the position resolution: upon some more thought, there may be a description in another standard for how to enhance any position data sent in a DSC radio message to another DSC radio. Most of the M.493 is describing how the radios are to communicate and interoperate. This is different from what the radios will produce as a data output on their serial ports, which is covered in another standard. Unfortunately, that standard is not an ITU standard, but a IEC standard, and you have to buy it--at a sizeable investment--to get the details. The IEC standard is really a re-naming of the NMEA standard, and again, you have to buy that to find out what it says. And, you have to agree to never disclose the contents.

I know that in the NMEA data messages output from a DSC radio on their data link, the position data in the sentence $DSC is only to one-minute of resolution, but if the $DSC sentence is immediately followed by $DSE then the position data is enhanced to a very small fraction of one-minute--about six decimal places as I recall without having to look it up.

You may find my four-part series or articles on how DSC radios work to be interesting reading; it starts here:

http://continuouswave.com/whaler/refere ... sTest.html

Re the thread's location in the forum hierarchy: yes, I was thinking of moving the discussion. I have moved it to VHF MARINE RADIO but left a shadow link in the original forum. I do that when I don't want to break any links to the original location that may be pointing to it from other websites. I also split off this discussion from the original thread as much of the discussion here is specific to one particular radio, the Standard-Horizon HX-890.

floehopper
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Re: Standard-Horizon HX890, CLASS-H DSC Radio

Postby floehopper » Fri Dec 14, 2018 2:49 pm

In case it's helpful, you can still access much of the content that was on the http://www.gmdss.com.au website using the Internet Archive's excellent Wayback Machine [1]. Looking at the site in 2017, the homepage says: "The GMDSS web site has closed, as the owner is now a gentleman of leisure" [2]. Please do consider submitting other useful websites to the Internet Archive and making a donation to support their excellent work!

[1]: https://web.archive.org/web/20161206150 ... ss.com.au/
[2]: https://web.archive.org/web/20170204193 ... ss.com.au/