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Author Topic:   DSC--Not Ready For Prime Time
jimh posted 09-15-2007 11:58 AM ET (US)   Profile for jimh   Send Email to jimh  
This spring I made a modest investment in a new VHF Marine Band transceiver for my boat, and I specifically bought one which was rated for CLASS-D DSC operation. DSC, or digital selective calling, is a new technology in marine radio communication, well, relatively new as it has been around for many years now, and it offers many advanced features. The short list is:

--Distress call broadcast with digital position information
--Selective calling of other parties using digital hailing channel
--Remote position polling and plotting of other vessels on my chart plotter

As for the Distress Call function, I have left that alone and trust that if I need it some day it will work as specified, but for the other two features, I hoped that I might be able to actually use them. Of course, to use a DSC radio you need someone with another DSC radio to communicate with you. To that end I strongly encouraged several boater-friends to get DSC radios so we could try this new technology.

My chance to test my new DSC radio came at a recent gathering of friends. Three fellow Boston Whaler owners showed up with DSC radios, making the perfect test situation. We were all moored on the same dock, almost in a row. What better chance to see DSC in action. I'll call my three test boats D, S, and C, as in "DSC."

The first test was an immediate bust. Although D had just bought a very nice DSC Class-D radio, he had neglected to register his vessel and obtain an marine mobile service identity (MMSI). Without an MMSI there is no way to use a DSC-Radio for digital selective calling purposes. There was no possibility of digital communication with this radio.

Next was S, who was certain his radio was programmed with his MMSI. However, no amount of digital calling from my vessel to his produced the slightest response from his radio. The reason for this was never determined. His radio just sat, silently ignoring my DSC calls. His radio also appeared to be a slightly older and non Class-D rated model.

Finally we tried C, who had another older radio, not quite Class-D rated, but one that alleged it had DSC capabilities. Here we had the first glimmer of success. When carefully observing the radio display panel, C's radio alerted him that he had received a call. However, the user interface of C's radio was so complicated that he was not familiar with the procedure to reply to the call, nor did his radio automatically switch to the working channel which my DSC call had specified be used. I am not certain if the radio provided any aural alert (a BEEP or something) to alert him that he had been called via the digital hailing channel.

After several tries this DSC radio interoperation test was abandoned, and we left the dock and went boating. So thus my 2007 boating season is almost over, and despite my new Class-D DSC radio which I have carefully configured with my MMSI, carefully connected to my GPS to provide position data, and carefully connected to my chart plotter to allow plotting of the position of other vessels, I am still awaiting my first actual use of digital selective calling for any useful purpose.

Am I boating in a digital radio backwater? This has gotten so frustrating (and the price of these radios become so cheap) that I am seriously considering buying a second Class-D DSC VHF Marine radio just so I can find out if my first one is working!

I would be pleased to hear the experience of other boaters with Class-D DSC radios. Please tell your story of modern recreational boating radio communications.

bdb posted 09-15-2007 01:31 PM ET (US)     Profile for bdb  Send Email to bdb     
"We were all moored on the same dock, almost in a row."

Too close? Even at low power you might have been blowing over one another.

davej14 posted 09-16-2007 11:13 AM ET (US)     Profile for davej14  Send Email to davej14     
I assume that these boats could communicate by manually tuning to the same channel. Is there a reason that DSC would not also work because of their proximity? This does not make sense to me.
jimh posted 09-16-2007 12:50 PM ET (US)     Profile for jimh  Send Email to jimh     
The radios involved in the test were from respected manufacturers, and, as I recall, we did not have a problem communicating with each other using the normal channels at close range with 1-watt. However, it did not occur to me that the nature of the digital selective calling (DSC) features might not respect the operator's setting of the radio transmitter power.

To clarify: I was assuming that when I selected the transmitter mode to go to LOW power, I was also forcing the digital selective calling feature to use this same power setting. But it might very well be that the digital selective calling feature always transmits at full power. If you think about, it is a very reasonable choice for the designer of the radio to make. If you are making a DSC call you might as well send the call request at maximum power. In this way you are most likely to reach the station you are calling.

I do not have my Class-D DSC radio handy to test this, but it will be interesting to see how it behaves in that regard. If the DSC call is transmitted at full power, then there may have been some problem in my test at the dock due to the very close proximity of the transmitters and receivers. It is all too common, unfortunately, that marine radio receivers do not tolerate extremely strong signals very well. I used to use a marine radio (from what I would consider a second tier manufacturer) and its receiver was so bad that I always had to ask the harbormaster to switch to low power in order that I could communicate with them once I got close to the harbor.

Following the at-the-dock test, I later tried again with one of the other boats when we were at a distance. However, in this case, the distance was at the point where we were just in radio range of each other. We tested this first by establishing regular voice communication on a channel. Then I made a DSC call request to the other radio, but obtained no acknowledgment from the remote radio.

My original inquiry was not particularly technical and was more or less a request for others to tell their user experience, but this question of the power in DSC calling brings up a corollary: is the range of communication with a typical VHF Marine Band radio the same on its voice channels as on its digital channel? There are many technical considerations to this answer. First of all, the human ear is a wonderful instrument for copying signals with poor signal to noise ratio, and it can out perform many purely electronic demodulators when it comes to extracting data. We have to compare that to the digital mode. Which has the longer range?

My radio's manual lists its emissions as


Using the definition of emissions from

I interpret these as follows:

16K0G3E means a 16-kHz wide emission using phase modulation to convey analogue telephony (voice).

16K0G2B means a 16-kHz wide emission using phase modulation to convey a single channel of digital data using telegraphy (teletype). This is probably frequency shift keying.

Which can get through better: PM voice or PM FSK at 16-kHz bandwidth. My seat-of-the-pants guess is that voice might be better on the fringe of a path. That is based on 44 years of actively using radios for communication as both a radio amateur and a professional Broadcast Engineer. Any communication engineers want to comment?

jimh posted 09-16-2007 01:29 PM ET (US)     Profile for jimh  Send Email to jimh     
I found more information about the nature of the digital selective calling emission. According to RECOMMENDATION ITU-R M.493-11 Digital selective calling system for use in the maritime mobile service,

1.3 The classes of emission, frequency shifts and modulation rates are as follows:

(for VHF)

1.3.2 Frequency modulation with a pre-emphasis of 6 dB/octave (phase modulation) with frequency-shift of the modulating sub-carrier for use on VHF channels:
– frequency-shift between 1 300 and 2 100 Hz; the sub-carrier being at 1 700 Hz;
– the frequency tolerance of the 1 300 and 2 100 Hz tones is ± 10 Hz;
– the modulation rate is 1 200 Bd;
– the index of modulation is 2.0 ± 10%.

So DSC is phase modulated frequency shift keying using a 1,700-Hz subcarrier and 1,300 and 2,100-Hz mark/space tones. The data is sent at 1,200-baud.

The digital encoding technique includes error checking provision. What digital encoding technique is being used? Is it SITOR?

Henry posted 09-16-2007 02:33 PM ET (US)     Profile for Henry  Send Email to Henry     

Is it possible to explain all that in laymen's terms?

BellBoyBob posted 09-16-2007 05:26 PM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
I performed a similar test using two DSC class d radios on two separate boats IN THE SAME GARAGE! One was my old Icom 402s and the other was my friends Icom 502 (NOT 502 A). Neither of these radios, we later came to understand, were capable of outputting NMEA for GPS polling. What I found in the test (with both radios programmed with MMSI numbers)was that the DSC "ping" alert worked on both radios but the receiver radio would not jump down to the selected channnel entered from the transmitting radio. When the 502 called the 402 with a position report, the 502's lat / lon came through on the 402's screen (but not, for reasons listed above, on my Garmin 178 screen). Realizing we had radios that could not output NMEA, we sold our old ones on E-bay and I purchased the SH GX3000S with NMEA in and out. I also downloaded a software update for the older Garmin 178 plotter / sounder that included NMEA in(DSE sentence). I have not been able to test the new system because my friend and his boat are back in Minnesota and I am in Rochester, NY. I will find SOMEONE on the water with a class D DSC radio connected to a polling GPS so I can really see if this works... New technology has its bugs - both in the equipment and in the sometimes confused brains of the equipments' owners! The idea behind position polling with DSC is so important in terms of safety. I hope that it will become the standard.
jimh posted 09-16-2007 09:37 PM ET (US)     Profile for jimh  Send Email to jimh     
Bob--It sounds like we are in the same boat. Maybe we can put our boats on the trailer, you drive west and I'll drive east and we can meet on Interstate 80 in western Pennsylvania on a couple of hilltops 30-miles apart. Then we can use our cellular telephones to coordinate a test and see if our DSC radio's work! (But this would be illegal--see below.)

It would be nice if there were some automated test station set up by the Coast Guard so that boaters could check the functions of their DSC radios by calling it. For example, if your local United States Coast Guard station had a DSC radio set up and published their MMSI, you could test your radio by giving them a digital call using DSC and requesting a position. The test radio would be configured to automatically reply with a known position, which would also be published. You could immediately verify that your radio was properly interfaced to your chart plotter and was working properly.

I may just set up my own test station like this so I can check my radio. The price of another Class-D DSC radio is not very high (about $125). A second-hand GPS ought to be very cheap. Technically, I shouldn't even need a GPS as I ought to be able to enter my position into the radio manually, although I bet that most Class-D radios don't have that option available. I will have to go read the manual carefully for mine to see if it does.

Technically, it would be in violation of the FCC regulations to set up an unlicensed station like this unless it were on a recreational vessel. If on shore it would have to be licensed as a marine shore station, and generally those licenses are not easy to get. So to do this legally I would have to buy myself a second recreational boat, take it down to the lake, and launch it.

The other irony of my DSC radio purchase is that in my area, the Great Lakes, the United States Coast Guard has announced that its shore stations here will be the last to be upgraded to the new RESCUE 21 radio system. So for the next few years my DSC radio will potentially be sending its distress calls to no official Coast Guard listeners. With a decent DSC radio now so low in price, you would think that each station ought to have one listening.

where2 posted 09-16-2007 11:41 PM ET (US)     Profile for where2  Send Email to where2     
Jim, if you really want to test this, let me know. My PS1000 is still in it's box. I'm sure I could get an MMSI number assigned for it, and let you borrow it for testing purposes. I'm sure you have an antenna kicking around.
BellBoyBob posted 09-17-2007 10:32 AM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Jim - This issue of DSC testing is so vexing that I just might be willing to take a road trip towing my boat to a meeting point with you somewhere in NY's southern tier to SEE if this technology works in the real world. An alternative would be to meet legally on some lake inbetween our respective homes to try this.
I know that Bluewaterpirate has posted many informative articles and videos showing the DSC technology in successful action. He seems to use the Icom class D DSC radios in his demos. But he uses the Garmin chartplotters as well, showing that different electronics manufacturers are compatible. I am currently using the Standard Horizon GX3000S Class D DSC transciever connected to the "updated" Garmin 178 Chartplotter / Sonar combo. By "updated" I mean there was a free software update on the Garmin website that enables the 178 to input NMEA from the radio. I now SHOULD be able to effect position polling on the GPS map from another boat running through the Standard Horizon IF I can find someone to send me a position report from a similarly equipped boat!
I would appreciate very much Bluewaterpirate's thoughts on these issues we have. In the meantime, on my next cruise out on Lake Ontario, I will stop by the the USCG center at the mouth of the Genessee river and ask for some help - if they are not too busy.
More later,
BellBoyBob posted 09-17-2007 11:00 AM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Another option: I could buy the SH HX600S handheld DSC radio (which I intend to do anyway - providing a radio back up), connect it to my Garmin GPS map 76 CS handheld(which has NMEA out)and test my main unit mounted on the boat. The QUESTION IS: Using the same MMSI number, could I "call myself" as it were? Or, for testing purposes, would I have to assign another MMSI to the handheld radio?
hauptjm posted 09-17-2007 11:02 AM ET (US)     Profile for hauptjm    

It would be nice if there were some automated test station set up by the Coast Guard so that boaters could check the functions of their DSC radios by calling it. For example, if your local United States Coast Guard station had a DSC radio set up and published their MMSI, you could test your radio by giving them a digital call using DSC and requesting a position. The test radio would be configured to automatically reply with a known position, which would also be published. You could immediately verify that your radio was properly interfaced to your chart plotter and was working properly

It seems the Coast Guard does in fact have live testing centers for DSC with MMSIs. See here:

jimh posted 09-17-2007 11:15 AM ET (US)     Profile for jimh  Send Email to jimh     
Unless I am reading it wrong, all of those stations are listening on MF/HF, not on VHF.
jimh posted 09-17-2007 11:17 AM ET (US)     Profile for jimh  Send Email to jimh     
From the cited page:


The USCG plan to implement GMDSS Sea Area A1 is one element of the USCG National Distress and Response System Modernization Project, now called "Rescue 21", which replaces the whole USCG VHF distress system. On 24 September 2002, Secretary of Transportation Norman Mineta announced the award of this $612 million contract to General Dynamics Corp.

Until this system is installed, the Coast Guard cannot reliably receive VHF DSC distress calls.

Buckda posted 09-17-2007 04:59 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Given the responses to this thread and the willingness of one participant to drive across several state lines to test his radio, it is my guess that not many people are using - or know how to use - this feature on their radios.

The radio makers haven't made it easy either. I'm planning to dump my radio on my project boat and find a better, multi-function radio/loudhailer that is DSC capable for my 18' Outrage over the winter. Perhaps then I'll be able to answer your radio's call Jim!


hauptjm posted 09-17-2007 05:36 PM ET (US)     Profile for hauptjm    
jimh, you are correct. The site I referenced is for MF/HF not VHF. Now, I'm confused. As Buckda states, is there not a "ready market" of these devices being used? I guess I assumed that this technology was fairly common to newer devices.
Thirsty Whaler posted 09-17-2007 08:17 PM ET (US)     Profile for Thirsty Whaler  Send Email to Thirsty Whaler     
Am I wrong, I thought that DSC receiving capabilities for USCG stations were not up and running on the Great Lakes yet?
Chuck Tribolet posted 09-17-2007 08:40 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Dollars to donuts C was an Icom. Don't blame DSC, blame Icom
for their dumb user interface. My SH sets itself to the
working frequency, rings like a telephone, pick up the mike
and talk.

You shoulda poked around in S to make sure that the MMSI was
really set, and set to what was expected.

Also, the CG's new system is operational in the following
* Atlantic City, NJ
* Eastern Shore, VA
* Mobile, AL
* St. Petersburg, FL
* Seattle, WA
* Port Angeles, WA

See .
And even if the CG doesn't get it, I'd guess that about half
the radios on the water now are DSC capable.


Buckda posted 09-17-2007 08:48 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Chuck -

You're right on my end. It's an ICOM, and it's going on the project boat this fall.


bluewaterpirate posted 09-17-2007 09:28 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
DSC Demo using ICOM 504 and 502 radios and Garmin 2206 and 545 GPS/Chartplotters.

ICOM 504/Garmin 2206 test radio ICOM 502

ICOM 504 rear mic version/Garmin 545 test radio ICOM 502


jimh posted 09-17-2007 11:39 PM ET (US)     Profile for jimh  Send Email to jimh     
I think Tom's demonstration video recordings are great, and so are the nice demonstration videos on the ICOM website:

Maybe they'll convince more people to upgrade to new DSC Class-D VHF Marine Radios. In the meantime it is lonely out here in the backwaters of the DSC radio revolution.

jimh posted 09-18-2007 08:47 AM ET (US)     Profile for jimh  Send Email to jimh     
Re having a second Class-D DSC radio to use for testing:

I was curious if my radio was able to transmit a vessel position without having a GPS connected to it via NMEA-0183 serial data connection. I found the answer in the instruction manual; the radio can be programmed manually with a location latitude and longitude. You also have to program a time for the position. So for the purpose of testing with a second radio, it would not be necessary to have a second GPS.

For the Standard-Horion GX1500S the procedure for manual input of a vessel location latitude and longitude is explained on page 55 of the owner's manual.

bluewaterpirate posted 09-18-2007 09:10 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Jim is absolutely right ..... I manually input all the data into my test radio ... it's very easy to do.
jimh posted 10-12-2007 07:36 PM ET (US)     Profile for jimh  Send Email to jimh     
Update on our DSC testing in the backwaters of the midwest:

Last weekend we did get two Class-D rated DSC radios to cooperate a bit further. I sent a DSC call request from my Standard-Horizon radio to a Uniden radio which had been configured with an MMSI. The Uniden radio alerted the operator that it had received a DSC call request. However, the operator was not totally familiar with the operating procedure of the Uniden radio and could not reply with a DSC acknowledgment. The DSC call was not completed.

We are inching closer to our first DSC call here in the digital backwater.

BellBoyBob posted 10-13-2007 02:49 PM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Jim - I, too, would like to hear acoounts of this system actually working in the real (water) world...I know Bluewater pirate demo's of DSC radios interfaced with various plotters shows that it works for both DSC calling and polling, but out there...?
I now made my purchase of the Garmin 540s (backed out of the 440s deal I thought I was going to make thinking I will purchase this GPS for at least five years worth of use - I want the bigger screen) and this will be interfaced with the SH GX3000S DSC radio with NMEA in and out. There is NO REASON why my gear will not do what I want it to now. Here's hoping!


jimh posted 10-05-2008 11:33 PM ET (US)     Profile for jimh  Send Email to jimh     
October 2008 UPDATE

After two seasons of boating with a VHF Marine Band Radio which supports Digital Selective Calling to Class-D provisions, I was finally able to actually initiate a digital selective call to another vessel, and also to receive a digital selective call from another vessel. Yeah!

The other vessel was not very far away--about 25 feet--and was using the exact same brand and model radio. And we coordinated the calls by yelling to each other. However, the technology worked--our radios responded to the digital selective calls as we hoped.

In addition, we were also able to check the remote position polling function between the radios. I could request a remote position poll from the other vessel, which, if a reply was authorized, resulted in my chart plotter displaying the position of the other vessel. Yeah! That worked, too.

The next phase of testing will be to find another vessel with a different brand of radio and see if the two will interoperate. Prior tests using mixed brands have failed, however, in those tests, neither vessel had previously confirmed its capabilities with DSC.

Bella con23 posted 10-06-2008 07:39 AM ET (US)     Profile for Bella con23  Send Email to Bella con23     
I happy to hear the outcome of your DSC test. I was beginning to wonder if the system worked at all.

I'm sure that it will vary from plotter to plotter, but what kind of indication did you receive on your plotter and was it immediate?

jimh posted 10-06-2008 08:57 AM ET (US)     Profile for jimh  Send Email to jimh     
When the DSC Remote Position information was transmitted to my vessel by other vessel, my chart plotter moved the cursor to the location of the other vessel, and the chart plotter also gave me several menu choices of what to do with the information. I am sorry I did not take careful notes, but I believe one choice was "GO TO VESSEL." I elected that option, but then the chart plotter told me that there where navigation hazards in the path and refused to comply. I did not explore that option further. A second option was something like "SAVE VIEW." When that option was selected the other vessel's position was plotted on the chart display. Later I noticed that the marked position was identified with the marine mobile service identify (MMSI) of the remote vessel. There was a third option, but I don't recall precisely what it said. Perhaps it was "IGNORE."

On my boat I have the DSC radio mounted below the helm station in the locker below the wheel. This keeps the radio out of the weather, and for general purposes it is a good location for the radio. But with DSC operation you need to have access to the controls of the radio and to see the display on the radio. With my boat's current configuration, the radio is in a awkward position for interaction like that. I may have to move the radio to a more prominent position at the helm station.

jimh posted 10-06-2008 09:03 AM ET (US)     Profile for jimh  Send Email to jimh     
I should also mention that the chart plotter and the radio are all from the same manufacturer, so, again, this tends to insure good interoperation, and in fact that notion influenced my choice of what chart plotter and radio to buy. I figured that if they were all from the same brand they would certainly be ready to work together.

At the other end of the circuit, the remote vessel did not have a chart plotter, and when I sent my position to that radio, the radio display presented my latitude and longitude on its front panel display.

The price of a Class-D DSC VHF Marine Band radio is now very modest, about $150, and I cannot imagine why anyone wouldn't get a Class-D radio when upgrading from their current radio or when buying their first radio.

bluewaterpirate posted 10-06-2008 09:22 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
I was offshore last weekend and observed a realtime DSC Emergency. Both of my ICOM 504's received the call and responded appropriately. One is connected to a Garmin 2206 and the other to a Garmin 545. Both ICOMS forwarded the position information to their respective chartplotters with all the appropriate data. The craft in extremis was 22 miles from my location. Radios switched to channel 16 and I was able to listen to the Coast Guard and vessel in distress communicate. The Coast Guard switched them to Channel 22. Other boats in the area responded to the DSC Emergency.

I regularly exchange positional/informational information to other boats in my area using DSC functionality. Most of these boaters use Furuno/Raymarine/Garmin MFD's connected to ICOM/SH/Uniden VHF radios. I have noted no interoperability issues between vendors when the equipment is connected and setup correctly.


jimh posted 10-07-2008 03:44 PM ET (US)     Profile for jimh  Send Email to jimh     
Tom--I think the offshore boaters you are encountering are more advanced than some of the inland boaters around the Great Lakes.

It's around 50-50 if most VHF Marine Band radios even work, in my experience. By "work" I mean they can transmit and receive around ten miles.

Using a Class-D DSC radio, what information other than position can be exchanged?

bluewaterpirate posted 10-08-2008 10:38 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
JimH .....

We use DSC as a means of talking to one another when we want to do it discretely. By this I mean we want to direct one or more of us fishing in the same area to a particular VHF channel without transmitting that information by VHF voice.

The way we do that it that we enter our friends MMSI #'s and names into our Individual Call List stored by our VHF radios. I have 31 friends that are programed into my ICOM 504's. When I want to talk to one or more I go to the Individual Call menu select the one(s) I want to talk with then select one of the prepramed channels we use for communications purposes (6, 8, 68, 77) and then transmit this data via DSC. On the other end they receive the DSC call they can do two things in acknowledgement:

1. Can Comply
2. Cannot Comply

If they choose can comply after they seen the response their radios will automatically switch to the VHF channel received in the DSC msg.

After that it's a matter of picking up the mics to talk.

There you go.


jimh posted 10-08-2008 03:33 PM ET (US)     Profile for jimh  Send Email to jimh     
Tom--OK, I understand. You are not exchanging any information by DSC, you are just using it to make a selective call, do it discretely, and then have voice communication on an obscure channel which is not likely to be monitored.

In Class-A DSC communication it is possible to send data via the serial data link between radios, and you can have remote printing. A home office can send a telegram to a vessel and have it print on the ship's printer. I thought you were transmitting data like that.

themclos posted 10-09-2008 12:45 PM ET (US)     Profile for themclos  Send Email to themclos     

Do you also use DSC to discretely transmit your location to a friend if there is a hot bite and you want to share your location only with him?

I thought this was possible as well.


bluewaterpirate posted 10-09-2008 01:19 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Yes we do that ........

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