Icom MA-500TR AIS NMEA0183 Sentences

[freaky930]

Hi!


I got an Icom IC-423 and would like to make DSC Calls directly from my Plotter.


I know that the MA-500TR is capable to initiate a call on any compatible ICOM Radio via its interface an a proprietary NMEA0183 sentence.


Does someone already know, what this sentence.qould be or does anyone have the MA-500TR and could log the communication between the Transceiver and the radio?


That would help a lot!


Kind regard and many thanks!

[stevead]

If it is anything like my old Icom 504, it will be a standard NMEA 0183 DSC sentence.

For obvious reasons I've never sent a DSC Distress Alert sentence to the radio but aeons ago when playing around, sending the Individual, All Ships, Position & Poll Request sentences to my radio all seemed to work.

[Statistical]

Originally Posted by stevead

If it is anything like my old Icom 504, it will be a standard NMEA 0183 DSC sentence.

For obvious reasons I've never sent a DSC Distress Alert sentence to the radio but aeons ago when playing around, sending the Individual, All Ships, Position & Poll Request sentences to my radio all seemed to work.

It isn't standard bcause there is no standard message for this (annoyingly).

To be clear the OP is asking about specifically initiating a DSC call by selecting a target on the MA-500TR. That uses some proprietary non-standard protocol only understood by specific Icom radios and only sent by the MA-500TR.

Note that other manufacturers do the same thing. A Garmin chartplotter can initiate a DSC call on an AIS target but only if you have a Garmin radio. Raymarine same thing but only Raymarine to Raymarine. If you have a Garmin chartplotter and icom radio no dice.

Annoyingly this 'could' easily just be a standard NMEA0183 or N2k message like the hundred or so other messages to allow cross brand interoperability but no standard message exists (likely because the big brands don't want it to).

[stevead]

Forgive me for misreading the OP's the original question!

I got an Icom IC-423 and would like to make DSC Calls directly from my Plotter.

I'll reiterate, assuming the OP's Icom IC-423 behaves like my older Icom IC-M504, upon reception of correctly formatted standard NMEA 0183 DSC sentences, it will initiate a DSC call.

The question that needs to be asked is "What is the OP's Plotter?" and is it capable of sending a standard NMEA 0183 DSC sentence to a connected VHF DSC transceiver ? If it is a commercial chartplotter, it is highly likely that it can't.

That uses some proprietary non-standard protocol only understood by specific Icom radios and only sent by the MA-500TR.

You are totally incorrect. My IC-M504 is one of the VHF DSC transceivers that is compatible with the MA-500TR and I can assure you that no proprietary NMEA 0183 sentences are used to initiate a VHF DSC call.

[Statistical]

Originally Posted by stevead

You are totally incorrect. My IC-M504 is one of the VHF DSC transceivers that is compatible with the MA-500TR and I can assure you that no proprietary NMEA 0183 sentences are used to initiate a VHF DSC call.

It works because there is a proprietary message and both the send and receiver understand it because they are both Icom. If you had any other chart plotter or Class A AIS from any other brand you could not use it to initiate a DSC call on the IC-M504.

Likewise Garmin has their own Garmin only message. Raymarine has their own Raymarine only message. B&G has their B&G only message, etc.

There are only two standard NMEA0183 sentences (messages) related to DSC that is "DSC" and "DSE" and both involve displaying data related to an incoming DSC message or emergency all ships message on the chart plotter not initiating a call from the chart plotter to the radio. DSC provides crude position along with other ship specific details and DSE provides additional high precision location if available. The same is true with N2K.

[stevead]

There are those that believe the science, and those that don't.

It works because there is a proprietary message and both the send and receiver understand it because they are both Icom.

I'm guessing that you don't own an Icom VHF DSC transceiver with a NMEA 0183 interface, otherwise you could verify for yourself that there is nothing proprietary about the sentence sent to initiate the call.

There are only two standard NMEA0183 sentences (messages) related to DSC that is "DSC" and "DSE" and both involve displaying data related to an incoming DSC message or emergency all ships message on the chart plotter not initiating a call from the chart plotter to the radio.

Again, you're wrong. From the NMEA 0183 standard:

This sentence is used to receive a call from, or provide data to, a radiotelephone using Digital Selective
Calling in accordance with Recommendation ITU-R M.493 (formerly CCIR Recommendation 493).

For example, the following initiates an Individual Routine call to a vessel with MMSI address of 235123456, requesting a call on VHF Channel 8.

$CDDSC,20,2351234560,00,00,26,900008900008,,,,R

Nothing mysterious or proprietary, just a bog standard NMEA 0183 DSC sentence.

I'll leave it as an academic exercise for you to calculate and append the NMEA 0183 checksum and to read through ITU-R M-493 to understand what it all means.

The only point in which you may be correct is that the commercial chart plotter vendors probably use proprietary sentences between their plotters and transceivers, but as I don't own either, I personally can't verify.

But congratulations on turning this into a pissing match that doesn't really address the OP's question.

[continuouswave]

Originally Posted by stevead

For example, the following initiates an Individual Routine call to a vessel with MMSI address of 235123456, requesting a call on VHF Channel 8.

$CDDSC,20,2351234560,00,00,26,900008900008,,,,R

Nothing mysterious or proprietary, just a bog standard NMEA 0183 DSC sentence.

I'll leave it as an academic exercise for you to calculate and append the NMEA 0183 checksum and to read through ITU-R M-493 to understand what it all means.

I studied the DSC recommendations in some detail and I believe I have deduced the format for the NMEA-1083 sentence "DSC". I explain the "DSC" sentence in some detail at

https://continuouswave.com/whaler/re...Datagrams.html

Using the cited example above, I interpret the example DSC sentence contents as follows, where each element is separated by a common from the other elements:

1. "$CDDSC" means this sentence is from a Communication device of type DSC, and the message is type is DSC.

2. "20" encodes the call type: INDIVIDUAL

3. "2351234560" is the nine-digit MMSI of the recipient with a zero appended

4. "00" encodes the message category: ROUTINE

5. "00" is interpreted depending on the message type; because this is a ROUTINE message the "00" is the first telecommand; the "00" indicates the mode of communication is F3E or G3E (all modes).

6. "26" encodes the second telecomand: "No information"

7. "900008900008" is an encoding of the channel identifier; I have not worked out the details of this field, but the "08" must be indicating VHF Marine Band channel 08. The "9" may be identifying that the number that follows is a channel number--just a guess. There is plenty of room in this field to send the frequency; I don't know why it is repeated.

8. [a blank field] this usually encodes the time the message was composed in UTC

9. [a second blank field] I have not determined this field's use

10. [a third blank field] Again, I have not determined this field's use

11. This segment usually encodes the end of message signal; "R" = acknowledgement requested

There are two missing fields in the example.

12. This field encodes the nature of the next message to be received; if the next message will be a DSE (adds more resoulution to position data) this field would be "E"

13. This field would be the checksum of the whole message. The suggestion that this will be an exercise is quite appropriate for me, as I have not figured out the algorithm to compute the message checksum. Also, it seems like some DSC devices just ignore the checksum.

This is the first actual example of a NMEA-0183 sentence that is said to set up a DSC call when sent to a DSC radio. I assume this works with a CLASS-D DSC radio. Thanks for adding this tidbit of information.

If this were the middle of winter, I would lash up my DSC radio to a terminal and experiment with sending the example message to the radio. But because it is almost the first week of real boating weather in the northern Great Lakes, I am going to direct more effort into getting the boat ready for launching.

[freaky930]

Thank you all! This is already a lot of information!
Since I own a Garmin Plotter, I thought it was.actually easier to interface it with the radio but apparently it isn't...