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Author Topic:   DSC-Polling
jimh posted 01-22-2006 12:42 PM ET (US)   Profile for jimh   Send Email to jimh  
A recent innovation in VHF Marine Radio Band radio communication has been the introduction of Digital Selective Calling (DSC). This function allows one radio to place a selective call to a particular other radio, and to transmit and receive digital information from that particular other radio. The design of DSC allows short text messages and even remote printing to occur. However, in small recreational vessels, most of the DSC capability is limited to Class-D, which implements some basic safety and position polling features.

VHF Marine Radios which have Class-D Digital Selective Calling (DSC) capabilities include a function where the radio can transmit the vessel's position to other vessels. Generally the radio does not have a means of determining the vessel position itself, and the radio requires that it be connected to a source of NMEA-0183 data that will provide the vessel position information. Typically a radio's NEMA-0183 INPUT is connected to an NMEA-0183 OUTPUT from the vessel's GPS receiver. The GPS is configured to transmit the proper data on this connection, and the radio listens to the data stream.

The vessel's position information is not transmitted continuously. The most common use is the transmission of the vessel position when the DISTRESS button has been activated. In that situation, the radio sends the vessel's position as part of the distress notification message which is transmitted. In addition to the vessels' position, the radio will also transmit the age of the position information and the accuracy of the data. This is a good design feature, as the vessel's GPS may have been disabled and might have old data on its output. Others who receive the data can assess its value based on its age and accuracy. The distress message is a broadcast message and will be delivered to all vessels with a DSC radio which receive the signal. It is somewhat ironic that the Digital SELECTIVE Calling feature is being used here in its most basic application as a non-selective or broadcast transmission.

This functionality and integration of the vessel's radio and GPS are the most basic implementation of vessel position polling. However, the design of DSC allows for other uses of this information in non-emergency situations. For example, a vessel may transmit its position information to a particular other vessel. In this way, two vessels may privately exchange their position information. In order for this to be done, the DSC radio must also have the ability to receive DSC messages and relay their contents on an NMEA-0183 OUTPUT. Typically this data would be sent to a Chart plotter device. (The chart plotter may integrated with a GPS receiver or could be a separate display device.) The chart plotter would then plot the position of the vessel on its display.

Not all VHF Marine Band radios have the ability to both send and receive DSC data. Typically, this feature is only offered on the more expensive models of DSC radios. Look for an indication that a particular radio has DSC position polling reception.

Also, not all chart plotters have the capability to display or plot the position of other vessels. Look for an indication that a particular chart plotter has an NMEA-0183 INPUT and will plot vessel position data it receives.

Let us assume we have two vessels which have the proper radio and chart plotters aboard, and they have been properly interconnected. What else is needed for the two vessels to exchange position data?

The first requirement is that the vessels have registered their DSC radios and obtained an Maritime Mobile Service Identity (MMSI). The MMSI is a unique registration number which is programmed into the radio. This identifier is used when the radio transmits (to identify the source of the transmission) and when the radio listens (to identify which messages are intended for that radio). Let's assume that both skippers have properly registered their radios and have obtained an MMSI.

Next, the MMSI must be programmed into the radio. Typically there is a special sequence for entering an MMSI into a radio. Be careful when programming a radio, as most devices do not permit the MMSI to be changed once programmed, or may only allow one change after initial programming! (In the U.S. there are federal regulations which require all radios sold to only allow the MMSI to be programmed twice by the user. This is probably to prevent capricious changes in a vessel's MMSI.)

Now the two skippers must exchange each other's MMSI in advance. In order to contact another vessel using DSC, you have to know that vessel's MMSI.

Finally, the MMSI of the other vessel has to be entered into the calling vessel's radio. The typical DCS radio on a recreational vessel does not have a full numeric keyboard for entering data, and this can make entry of the MMSI somewhat tedious to accomplish, particularly at sea. Thus it will most likely be necessary to pre-program the MMSI of the other vessel into your radio before leaving the dock. The typical process on a radio without a numeric keypad will probably involve a lot of additional keystrokes and button press combinations.

Now we are ready for our two vessels to exchange position information. Let's review the preparations needed on both vessels:

--DSC radio with input for position transmission
--DSC radio with output for received position
--MMSI registration of vessel
--MMSI programmed into vessel's radio
--GPS output connected to radio input
--Chart plotter with input for external position plotting
--Chart plotter connected to radio
--Other vessel's MMSI known
--Other vessel's MMSI programmed into radio

And one final factor: both vessels have to be within radio range of each other! For most small recreational boats with antenna heights around 6-feet, this means the two vessels will have to be within about 8-miles of one another. Let's call them vessel-A and vessel-B to keep track.

Ready? Let's exchange position data. The procedure is as follows:

Vessel-a sends a POSITION REQUEST CALL to vessel-B. We'll use an ICOM radio as a typical radio and demonstrate the process:

--Push DSC•POS to enter the DSC menu;
--Push [↑] or [↓] to select POS REQuest
--Push DSC•POS
--Push [↑] or [↓] to select the desired pre-programmed individual address;
--Push DSC•POS to enter the standby condition for Position Request Call; (channel 70 is selected on the radio and READY appears at the channel comment indicator;
--Push DSC•POS to transmit the Position Request call;
--After the Position Request call has been transmitted, the following indication is displayed: WAIT ACk
--Push any key to exit.

OK, our message has been sent. Assuming vessel-B is within radio range and is listening, the following will occur at that end (again assuming the use of a similar ICOM radio):


While monitoring Channel 70 and a Position Request call is received on vessel-B:

--DSC appears and RCV POS REQUEST scrolls at the channel comment indicator;
--the BEEP sounds for two minutes; press any key to stop the beep;
--Push DSC•POS to reply to the call; push any other key to ignore.

Back at vessel-A, he is now receving a reply to his request:


While monitor Channel 70 and a Position Request Reply call is received:

--DSC and POS REPLY appears in the display;
--the lattitude and longitude of vessel-B appear in the channel comment indicator and scroll across, showing first the latitude coordinate and then the longitude coordinate;
--the BEEP sounds for two minutes; press any key to stop the beep;
--Push DSC•POS to reply to the call; push any other key to ignore.
--the BEEP sounds for two minutes; press any key to stop the beep;

If vessel-A has his chart plotter turned on, the position of vessel-B should be shown. Repeat all of the above to exchange positions in the other direction.

jimh posted 01-22-2006 12:59 PM ET (US)     Profile for jimh  Send Email to jimh     
The best bet to making this all work is probably to limit the whole system to a single brand of devices. For example, I am quite sure that if you use a Standard-Horizon GPS/chart plotter and a Standard-Horizon radio on both vessels, this will all work.

I would be interested to hear reports from people who have actually done this, and if they had success with inter-operation among various brands of radios, GPS receivers, and chart plotters.

At the moment, on my vessel, I do not have a VHF Marine Band radio with the proper DSC capabilities, so I have not experimented with this. I have been giving some thought to getting a fancier radio as part of a general upgrade of the radio on the boat. I could then implement this set up. However, the problem is that you need some boating buddies who have similar set-ups, or there is not much point to going to all the expense and bother.

I am afraid at the moment the people with whom I do most of my boating are in the category of "radio-challenged" and are probably not candidates for this. And by that I don't mean to insult them. It's just that they are in the same boat (bad pun) with the vast majority of recreational boaters.

Perhaps we can have an informal survey: anyone with a DSC position polling radio and chart plotter set up, please sign in!

jimh posted 01-22-2006 01:53 PM ET (US)     Profile for jimh  Send Email to jimh     
Vessels that want to exchange positions using DSC don't necessarily have to go through the request and reply procedure I outlined above. A vessel can initiate the transmission of its position to another vessel on its own. Using the ICOM radio as an example, there is the procedure:

--Push DSC•POS to enter the DSC menu;
--Push [↑] or [↓] to select POS REPORT
--Push DSC•POS
--Push [↑] or [↓] to select the desired pre-programmed individual address;
--Push DSC•POS to enter the standby condition for Position REPORT Call; (channel 70 is selected on the radio and READY appears at the channel comment indicator;
--Push DSC•POS to transmit the Position Request call;
--After the Position Request call has been transmitted, the following indication is displayed: WAIT ACk
--Push any key to exit.

If both vessel-A and vessel-B spontaneously did this, they would both have each other's position. This cuts down the number of button pushes needed.

bluewaterpirate posted 01-22-2006 02:03 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Basic DSC funstionality resides in the VHF radio and not in any GPS/chartplotter which has already been pointed out. That is very important to remember!

Here are the three equipment scenarios that work. Will work from the worst case to best case:

WORST CASE: You have a Class-D VHF radio and a GPS/chartplotter that is NOT connected to your radio. The operator would have to manually enter their lat/long and time into the radio if:

a. they had an emergency and needed to use DSC feature or
b. they had a position request from another radio.

You can still use the DSC feature as long as you know the other boater's MMSI. The other boater's MMMSI, position, and time of position in the display window of your VHF radio.

MIDDLE CASE: You have a Class-D VHF radio that receives NMEA output positional data from the GPS/chartplotter that is not DSC compatable.

You will have full automatic DSC functionality with one exception. Your GPS/chartplotter will not be able to DSC report page and display the other boat's position.

In this scenario you will view the other boater's MMSI, position, and time of position in the display window of your VHF radio.

BEST CASE: You have a Class-D VHF radio that receives NMEA input positional data from the GPS/chartplotter and transmits DSC information back to the GPS/chartplotter.

You will have full two-way automatic DSC functionality between the radio and GPS/chartplotter. In addition to being able to see the responding boat's data in the display window of your VHF radio, your GPS/chartplotter will display two data windows.

The first is the DSC Report Page that will display the other boat's MMSI, the date and time of the tranmission, a magnetic bearing and range to the responding unit, and a lat/long of the responding unit. When finished reading that you depress a button to display the chart position of the responding boat.

The first thing you have to do after purchasing an Class-D VHF radio is apply for an MMSI. You can apply through Boat US or Sea Tow Web Sites--it's free. Class-D VHF radios are cheap. I just purchased and installed a Standard Horizon Phantom 1000 Hideway model for $133.00 (shipping included). See the pics below: sitebuilderpictures/2006_0107standardinstall0004.jpg

All your DSC caller request information can be preprogramed into you radio prior to leaving the dock. In another call scenario you can use the "Call All Ships" feature to alert other boaters as to hazards to navigation ("Securité, Securité, Securité" call on VHF channel 16 or 22) or if you have a problem but not a real emergency ("Pan, Pan, Pan" call on VHF channel 16 or 22). Using this method you don't need to know the other boats' MMSI. By the way. it is easy to program your MMSI into you radio.

It's just as simple to mix and match vendors equipment as it is to stay with one vendor when connecting your equipment. I used to exchange positional as well as communications information with my fishing buddies all the time. Very easy to use once you understand the basics. Been around for three years.

There you go.


jimh posted 01-22-2006 02:36 PM ET (US)     Profile for jimh  Send Email to jimh     
Tom--Thanks for the tip on the Standard-Horizon Phantom radio. That has to be the least expensive DSC radio that has the position polling feature. You do not get that feature set in the ICOM line until you move up to one of their premium radios like the M422.

Standard Horizon Phantom 1000 Radio


The two radios sell at quite a difference in price.

bluewaterpirate posted 01-22-2006 02:51 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
If you have limited helm space the Phantom PS1000 is the way to go because the radio itself is installed inside your console. It is easy to hear the mic speaker is amplified. It is as loud as my ICOM 502 with an external speaker. This is what the install looks like on my Ventura. sitebuilderpictures/helm1.jpg


jimh posted 01-22-2006 02:59 PM ET (US)     Profile for jimh  Send Email to jimh     
From reading the specifications, I don't think the PS-1000 has a second full-time receiver on Channel-70. That is a plus for the bigger ICOM.
jimh posted 01-22-2006 08:41 PM ET (US)     Profile for jimh  Send Email to jimh     
I just noticed that ICOM has a web page with links to several videos which demonstrate DSC features on their radios:

Riptide23WA posted 01-22-2006 09:51 PM ET (US)     Profile for Riptide23WA  Send Email to Riptide23WA     
Great tpoic, Jim. I have been interested in this feature, as I can see where it would be nice if several boats went out offshore. We could spread out over several miles, yet keep track of where the other boats are.

I have been considering the Raymarine C series multifunction displays, and buried in the literature somewher is mentioned DSC position polling display. The only Raymarine radio that seems to provide the required input is the 240 handset style. Raymarine hasn't responded to questions whether the display would work with other radios.

Will follow this thread....

bluewaterpirate posted 01-22-2006 11:07 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Go with an ICOM or Standard Horizon Class D VHF Radio. More bang for your buck. Raymarine makes great gsp/chartplotters. It's simple to connect the required NMEA connections with either vendors vhf radio with any Raymarine gps/chartplotter.


jimh posted 01-22-2006 11:36 PM ET (US)     Profile for jimh  Send Email to jimh     
More on some ICOM radios:

In the ICOM line it appears that these are the models which currently have position polling receive capability:

M502A (but not M502)

More on the Channel-70 receiver distinction:

The better DSC radios actually have two receivers built into one chassis. One receiver is paired with the transmitter, and listens to the channel selected by the channel selector. The other receiver is dedicated to listening to Channel-70 for DSC transmissions from other vessels. If the radio does not have the dual simultaneous receiver function, then it only listens to Channel-70 when it is not actively listening on another channel. You could say it is set to always scan Channel-70 when it is available to do so.

The dual-receive radios maintain a watch on Channel-70 all the time. This means you won't miss a DSC call even if you are chatting on some other channel when it comes in. Usually this capability comes only in the top of the line radios. The ICOM M602 definitely has the capability. It looks like no other ICOM radio has the dual receive; they use a dedicated scanning of Channel-70.

jimh posted 01-23-2006 12:00 AM ET (US)     Profile for jimh  Send Email to jimh     
More on some Standard-Horizon radios:

The current Standard-Horizon radios which have the position polling receive function appear to be:


As mentioned above, the PS-1000 is the low-cost price leader in this category. This radio is available for about $135.

The only Standard-Horizon radio with DSC Class-D dual receive capabilities appears to be their new PS-2000. This looks like a very nice radio set up for DSC, particularly when used with the VH-310 handset accessory, which includes a full numeric keypad for easier entry of MMSI data.

Chuck Tribolet posted 01-23-2006 12:06 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
The procedure is simpler on the my SH Intrepid:

--Push CALL to enter the DSC menu;
--Push [↑] or [↓] to select POS REQuest
--Push [↑] or [↓] to select select who you want to poll
--Push CALL to send the request


Channel 70 is monitored at all times.
When a Position Request call is received on vessel-B, it just
answers, no operator intervention is required. A mode can
be set where operation intervention IS required if you want
to hide your fishing spots.

SH has much better human factors than Icom. This applies
to both position requests and DSC voice calls.

How much accuracy is in the displayed position? Last I looked,
it was only accurate to one minute of lat/lon, about a mile.

Most recent Garmin GPSs will display the position. In some
cases a firmware update is required.


jimh posted 01-23-2006 12:52 AM ET (US)     Profile for jimh  Send Email to jimh     
Chuck--I reviewed the video from the ICOM website (see hyperlink above) which demonstrates a Position Request Call. When the other vessel responded, the ICOM radio displayed the vessel's position to three decimal places in the minutes field. This would be a resolution of just a few feet.

Perhaps this varies with radios. Tom has two brands of radios in his system, and I am sure he will comment on this.

Chuck Tribolet posted 01-23-2006 01:49 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Correction: I have an SH Spectrum (not Intrepid).

So add the Spectrum (no plus) to the list of radios that
support this.

Also, the SH Quantum GX3500S supports this function.

And finally: My radio manual only shows it supporting position
to minutes (no decimal). However, it actually shows my
position to .001 minutes. Whether it does this for position
requests is unknown -- a while back I dug up the data formats
that are actually transmited, and it only went to one minute,
no decimal. I'll have to run an expermiment.


jimh posted 01-23-2006 09:32 AM ET (US)     Profile for jimh  Send Email to jimh     
Radio Classifications for DSC:

Excerpt from a recent US Coast Guard meeting on DSC radios:

"The emerging international standard for Class D VHF-DSC... is... recommended for vessels which use DSC on a voluntary basis and is considered far superior to the RTCM SC-101 format which is the minimum acceptable standard for equipment sold in the U.S....The superior Class D should be encouraged in preference to the minimal SC-101 type. The Task Force agreed to advocate the use of Class D VHF-DSC for voluntary users rather than SC-101."


Executive summary: A radio with a DSC Class-D rating is preferred.

Moe posted 01-23-2006 12:46 PM ET (US)     Profile for Moe  Send Email to Moe     
I don't know of any VHF radio that can transmit DSC that cannot also receive it. The lower-priced Icom 302, 402, 402S, and older pre-a 502 can all receive and reply to position requests, if they have a GPS connected to their NMEA input. They also receive and display (on their own display) position data in replies to position requests they previously sent, but they do not have NMEA output and cannot send that information, or the position in a distress call, to a GPS. Additionally, the newer bottom-of-the-line 302 can receive position reports and position report replies.

DSC radio is certainly capable of communicating position data with greater accuracy than minutes, but whether you can send and display that data depends on your equipment's NMEA capability. If it only supports the NMEA sentence DSC, that only covers degrees and minutes. But if it also supports the extended DSC sentence, DSE, that contains an 8 character word containing two four digit values of ten-thousands of a minute for latitude and longitude.


jimh posted 01-23-2006 01:40 PM ET (US)     Profile for jimh  Send Email to jimh     
Moe--Have you actually seen those radios receive and display a DSC Position call on their displays?
Moe posted 01-23-2006 01:46 PM ET (US)     Profile for Moe  Send Email to Moe     
No, but I have read the Owner's Manuals which cover how to do that.


bluewaterpirate posted 01-23-2006 02:23 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Moe is right ....... the COM 302 & 402 models can all receive and send DSC positional/informational protocol.
The old 502 could only receive/transmit postional info in dd mm format. That model has been out of production for 2 years. ICOM has now dropped the A designation on the current 502 model. I'll post some info when I get home tonight.


Moe posted 01-23-2006 02:30 PM ET (US)     Profile for Moe  Send Email to Moe     
I should also add the 302 and 402 support DSC Watch, which monitors DSC while you're receiving a signal on another channel. If a distress call is received, they then alternately monitor channels 16 and 70 until the distress signal disappears.

I have no idea, but I'd be surprised if they used a second receiver to do this, when they could periodically retune the local oscillator to Channel 70 for a millisecond or so and check for IF signal during that short period.


bluewaterpirate posted 01-23-2006 05:16 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
My equipment uses the following formats

ICOM502 displays position as dd mm.mmm'/ddd mm.mmm'

Phantom 1000 displays position as dd'/ddd'

Both radios can send & receive NMEA data to/from the GPS/Chartplotter. Each radio will default to the position format it can receive.

Here's how my setup.

My Raymarine RC435 GPS/Chartplotter can only send NMEA data to my newest ICOM502 in dd mm.mmm/ddd mm.mmm format which the ICOM502 can display. (Note: The RC435 is not DSC compatible so it can't receive NMEA data from the radio).

My older ICOM 502 (bought in 2002) could only display the Ray position NMEA output as dd mm/ddd mm even though the Ray was sending ddd mm.mmm format.

My Phantom 1000 receives NMEA position info from my Garmin 376c in ddd mm.mmm format but can only display it as dd My Garmin 376c is DSC compatible so it can receive NMEA data from the radio).

My Raymarine 435 NMEA position output is a static setting, whereas, my Garmin 376c NMEA output is dynamic. Under the Advance NMEA Setup page on my Garmin I can choose from three Lat/Long Minute Precision Settings and they are:

The newer DSC compatible GPS/Chartplotters all have the Advanced NMEA Setup capability. From this page you can change baud rates, turn NMEA sentences on/off, and of course change the position format.

Fruit for thought:

You can take the following position data and transpose the figure from a degrees/minutes format to a degrees/minute/seconds format.

34 35.786'N 076 45.020W by multiplying the 3 digits to the right of the decimal point by 60. The 60 number represents 60 second = 1 mile.

.786 x 60 = 47.16''
.020 x 60 = 01.2''

So you would end up with this position when it comes to the accuracy question from the post above:

34 35' 47.16'' N 076 45' 01.2'' W

There you go ..


jimh posted 01-23-2006 07:31 PM ET (US)     Profile for jimh  Send Email to jimh     
Moe writes:

"I have no idea, but I'd be surprised if they used a second receiver to do this, when they could periodically retune the local oscillator to Channel 70 for a millisecond or so and check for IF signal during that short period."

A superheterodyne receiver just needs a separate local oscillator, mixer, and intermediate frequency amplifier chain, and it can easily be made to be a dual channel simultaneous receiver.

There are other problems with the rapid switching of the local oscillator frequency. Upgrading the synthesizer section of the radio so that it can make very rapid and relatively large jumps in frequency with out increasing the noise sidebands of the oscillator signal takes careful engineering. If the noise sidebands of the injection signal are not extremely low, the radio's resistance to intermodulation distortion will suffer, and the receiver performance will degrade. The details of the innards of these radios are not really of much concern to boaters, so I do not see much reason to go further into them.

Suffice it to say that a radio which uses a rapid channel switching technique to monitor a second channel is a pain to use. The audio output of the primary channel will suffer from the periodic interruptions. It does not make much difference while the radio is squelched, but it does when the radio is actively listening to another channel. The dual receiver approach is superior, and it is the recommend minimum for recreational boaters now, per revision of the FCC rules and the U.S. Coast Guard's endorsement to boater.

jimh posted 01-23-2006 07:40 PM ET (US)     Profile for jimh  Send Email to jimh     
Looking at the DSC-Radio market with an eye to the present and not the past, I think it is important to note the following:

• The United State Coast Guard is recommending Class-D as a minimum for recreational boaters who want to equip their vessels with a DSC radio;

• The only ICOM radio that is Class-D rated is the M-602;

• The Standard-Horizon PS-2000 is rated Class-D.

bluewaterpirate posted 01-23-2006 08:55 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Rescue 21 status as of January 2006, the USCG's new state of the art communications system:

Chuck Tribolet posted 01-23-2006 09:08 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
The Standard Horizon Quantum GX3500S is Class D.


bluewaterpirate posted 01-23-2006 09:23 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Lowrance is also stepping up to the plate in 2006 with their new LVR-950 Class D Radio. It will list for $160.00


jimh posted 01-23-2006 09:36 PM ET (US)     Profile for jimh  Send Email to jimh     
More on choosing a radio for DSC use in the U.S.. I found this on a manufacturer's website:


"The [radio model] meets the internationally recognized requirements for RTCM SC-101 Digital Selective Calling."


The RTCM SC-101 was only recognized in the U.S., and that has since been withdrawn.

Chuck Tribolet posted 01-23-2006 09:38 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
It will be interesting to see what the real differences
between SC-101 and ITU Class D are.


jimh posted 01-24-2006 08:46 PM ET (US)     Profile for jimh  Send Email to jimh     
McMurdo has a Class-D DSC radio available. ID=1009

jimh posted 01-24-2006 09:02 PM ET (US)     Profile for jimh  Send Email to jimh     
Tom--The Lowrance LVR-950 Class D radio is mentioned in that May 2005 press release, yet here we are in January of 2006 and the radio is still not listed on the Lowrance website.
bluewaterpirate posted 01-24-2006 09:24 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
I've heard Lowrance LVR-950 Class D radio is to be released at the Miami Boat Show. I was wondering the same thing. Sounds like you are having a good time.


phatwhaler posted 01-25-2006 11:29 AM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
If you guys are interested in a Class A DSC radio to compare specs with, here is a fine example.

The Ross DSC 500.
(Bottom of the page)

I had one on my Shamrock a few years ago but never used any of the DSC features. Mainly because no one else was equipped with DSC back then. Most Coast Guard cutters have these radios on the bridge. Also, the Tampa Bay pilots have them installed in Pelican cases that they take onboard ships so that ship traffic can be monitored. Overall these things are overkill for us, but if you're a techy they're pretty cool.

When Ross still owned the company they were selling for around a thousand bucks. Now that L3 bought out Ross, I think the price has doubled. Actually, Ross Norsworthy is a pioneer in the development of all of this DSC stuff.

phatwhaler out.

CHRISWEIGHT posted 01-25-2006 06:00 PM ET (US)     Profile for CHRISWEIGHT  Send Email to CHRISWEIGHT     
ICOM showed a new Class-D DSC VHF Marine Band radio at the London Boat Show which claims to have a dedicated Channe-70 receiver. The model M505 looks like a nice unit and will be competitively priced.

A Review of the New ICOM M-505

Regards, Chris

jimh posted 01-25-2006 08:07 PM ET (US)     Profile for jimh  Send Email to jimh     
Chris--Thanks for the tip on the ICOM M-505 radio. This radio will not be available in the United State, however, I anticipate that ICOM will soon introduce a similar model at the Miami International Boat Show in February. I am looking for more details on that radio and will follow up when they become available.
Mike Brantley posted 01-25-2006 10:20 PM ET (US)     Profile for Mike Brantley  Send Email to Mike Brantley     
I saw this online retailer's page with the new Icom IC-M504 mentioned on another boating site...

ICOM M504 Radio

I believe Uniden's similar radio has driven price down and features up for Icom. I'd rather have an Icom or Standard Horizon because of reputation.

I have the original IC-M502 without the NMEA out wire. I had been considering getting the Icom IC-M422 model so I would have that function as well as the built-in hailer capability on my Revenge. But I think I would rather have this new model and use my older radio as a backup/secondary radio on the boat. I like the big rotary knob for channel selection that's on the 502 and the new 504, but not the 422.

I am assuming the 504 is the U.S. version of the 505 model referenced here.

jimh posted 01-25-2006 10:34 PM ET (US)     Profile for jimh  Send Email to jimh     
Ignoring for a moment the DSC portions, the NMEA-0183 inputs and outputs, and the user interface, ICOM radios have a good reputation for being very solid radios, that is, they are excellent receivers and transmitters. Many comparative tests rate them better at the radio portion of their tasks than competitors.

It is good to see they are about to introduce a new radio, which I presume will be DSC Class-D rated. This product will fill a gap in their line in terms of features vs. cost.

I like the rotary channel selector knob. I would prefer a numeric keypad for entering MMSI information, but I suppose it is not done that often--not as often as punching in a telephone number on a cellular telephone.

The collective news gathering ability here is impressive. Keep those new Class-D radio announcements coming.

bluewaterpirate posted 01-26-2006 02:27 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
The Ray54 VHF is Class D rated.


Chuck Tribolet posted 01-26-2006 03:11 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
MMSI info is entered very rarely. For me, about seven times
in the five years I've had the radio. Once for my own MMSI
and about six times to put MMSIs into the address book. It's
not a big deal with up/down buttons, or spinning a knob.


bluewaterpirate posted 01-26-2006 06:25 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Icom M-504 Picture


jimh posted 01-26-2006 08:38 PM ET (US)     Profile for jimh  Send Email to jimh     
I hope ICOM has that radio priced right when it finally comes to market. As it stands now with their actually announced radios, they are way out in left field with pricing for a Class-D radio. They need to come in at $200 to be price competitive. People may pay a bit more for an ICOM, but there are a number of new Class-D radios selling for $200 or less.
jimh posted 01-26-2006 08:43 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is more information on the RAYMARINE Ray54 VHF Marine Radio that meets DSC Class-D requirements:§ion=2& page=830&product_id=1750

The list price on this radio is only $215, so it should be available for under $200 at most discount marine providers.

Riverwhaler posted 01-26-2006 10:01 PM ET (US)     Profile for Riverwhaler  Send Email to Riverwhaler     
I own a Uniden UM525 that has a second receiver. The Uniden UM525 is probably not on everybody's first choice list but it really deserves a look. Lots of DSC features. It is Class-D rated. The UM525 includes a separate radio receiver for the dedicated DSC channel 70 which means you'll never miss an incoming DSC call.
jimh posted 01-26-2006 11:51 PM ET (US)     Profile for jimh  Send Email to jimh     
Fundamental Distinction of Class-D DSC Radios:

All VHF Marine Band radios which are rated DSC Class-D are required to have two receivers so that they can maintain a continuous radio watch simultaneously on Channel-70 (for DSC calls) and on Channel-16 (for voice calls in Distress). In Class-D it is not required that the radio maintain a watch on Channel-70 while it is transmitting on another channel.

The ability to have simultaneous dual reception is the most significant difference between the Class-D rating and the earlier DSC categories under which radios were sold in the United States.

There are a number of other refinements in the Class-D recommendation which further enhance the radio's performance for use in the Global Maritime Distress and Safety System (GMDSS). (I am working on a comprehensive summary of these features and will be publishing an article on this in the future.)

A Bit of History

The development of improved disaster radio communications has been an evolving goal since the 1974 International Convention on the Safety of Life at Sea (SOLAS). Commercial ships have been required to be equipped with sophisticated DSC radio systems for some time. In an effort to attract more recreational vessels to equip themselves voluntarily with DSC radios, the initial requirements in the United States were made very simple so that the cost of a DSC radio would not be excessive. In this way, recreational vessels could also take advantage of the improved safety that results from using a DSC radio.

Early DSC radios available were limited to just transmitting DISTRESS broadcasts using DSC techniques, and not much else.

As the cost of equipment was reduced, the FCC and USCG have coordinated to increase the recommended level of compliance. This has finally resulted in the situation we have now, in 2006, almost thirty years after this initiative was begun. A Class-D DSC radio can now be purchased for about $200, which is actually less than most VHF Marine Radios cost just a few years ago.

Unfortunately, while it appears that the recreational boater can now outfit his vessel with a very capable Class-D DSC radio, in the United States we are still waiting for our maritime safety agency, the U.S. Coast Guard, to complete a massive update of its radio system so that it will be able to receive those DSC DISTRESS calls. This effort is known as RESCUE 21. It was initially anticipated to be operational by c.2007, but this has since been delayed. Final rollout of RESCUE 21 may not be complete until much later due to complications with the technology of the system and cost overruns.

Even without a Coast Guard radio watch guaranteed on Channel-70 in all U.S. Coastal and inland waters, I think it is prudent to equip a recreational vessel with a Class-D DSC radio. The more recreational vessels that are equipped, the more we can all keep a lookout for each other in DISTRESS situations.

CHRISWEIGHT posted 01-27-2006 02:52 PM ET (US)     Profile for CHRISWEIGHT  Send Email to CHRISWEIGHT     
This is how radio is changing here in the United Kingdom and I suspect long term elseware. This passage was taken from the U.K. MCA (Maritime Coastguard Agency) website.


16.5 The Global Maritime Distress and Safety System (GMDSS) was implemented on 1 February 1999. The implementation of the GMDSS has involved the adoption of Digital Selective Calling (DSC) for distress alerting in maritime radio frequency bands – e.g. VHF. While the United Kingdom Coastguard will continue coverage of VHF Channel 16 for the foreseeable future, from 1 February 2005, the Coastguard watch on Channel 16 will be downgraded from a dedicated headset watch to a loudspeaker watch. Also, from this date, ships that are currently obliged to keep a listening watch on Channel 16 where practicable, will no longer be obliged to do so. Where it is considered that VHF should be fitted, with reference to Section 16.2, it is strongly recommended that vessels are equipped with VHF DSC with its significant benefits in distress situations by February 2005.


It is clear that at some point channel 16 certainly here may be given no more attention than any other channel and that safety will rely on DSC being fitted to all vessels.

Regards, chris

jimh posted 01-28-2006 12:30 PM ET (US)     Profile for jimh  Send Email to jimh     
More information on DSC Class-D radios is available in a new article in the REFERENCE section. Included is a brief summary of how Class-D radios differ from radios which met RTCM SC-101 recommendations. See

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