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Old 21-04-2014, 13:34   #1
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NMEA-0183 Sentences DSC, DSE

The most comprehensive non-restricted source of information about NMEA-0183 that I am aware of is found at

NMEA Revealed

but this reference is silent on the details of NMEA-0183 sentences DSC and DSE. If anyone has information about those two sentences that they can share, I would appreciate hearing from you.
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Old 21-04-2014, 15:11   #2
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Re: NMEA-0183 Sentences DSC, DSE

To learn more about these sentences I captured the NMEA-0183 output of a modern digital selective calling radio which had just received a call and was transmitting data from the call to a chart plotter via NMEA-0183.

The call was from a vessel with the following characteristics

MMSI = 338040079

Latitude = 42-degrees 31.456-minutes North
Longitude = 081-degrees 12.451-minutes West

The call was sent about 4:21 PM EDST.

The radio sent the following two NMEA-0183 sentences to the chart plotter:

$CDDSC,20,3380400790,00,21,26,1423108312,2021,,,B, E*73
$CDDSE,1,1,A,3380400790,00,46504437*15

The first sentence is NMEA-0183 DSC; the second is DSE.

Let's look at the structure of the DSC data. It is believed to contain the MMSI of the sender, and the position of the sender to whole minute resolution:

$CDDSC,20,3380400790,00,21,26,1423108312,2021,,,B, E*73

The code $ is the start delimiter, marking the beginning of the data packet. Other elements of the packet are separated by commas.

The code CD is the Talker ID. This indicates the talker is a Communication device of the type Digital selective calling.

The code DSC identifies the type of packet. I don't know the formal name for this in NMEA documentation.

The code 3380400790 is the marine mobile service identity of the station that sent the data to the radio, with an extra "0" appended.

The code 00 is unknown to me.

The code 21 is unknown to me.

The code 26 is unknown to me.

The code 1423108312 appears to contain the latitude and longitude to a resolution of whole minutes, with a "1" prefixed. The latitude is 42-degrees 31-minutes and the longitude is 083-degrees 12-minutes. The "1" appears to be an indicator perhaps of the N-S nature of the latitude or perhaps the quadrant.

The code 2021 appears to be the time of the message in GMT. (This was sent about 1621 local time, keeping GMT -4, so GMT time would be 2021.)

The code ,,, is unknown to me; it appears to represent missing parameters that were not sent.

The code S is unknown to me. Perhaps it means the position was obtained from a satellite signal source, such as GPS.

The code E*67 appears to be a check sum to allow the packet to be checked for accuracy by parsing of all the elements.

Now we look at the DSE packet. This is believed to contain expansion data for the position. The code is

$CDDSE,1,1,A,3380400790,00,46504437*15

Again the code $CDDSE is the start delimeter, talker type, and packet name.

The code sequence 1,1,A, may be as follows: the first "1" is the number of packets that are contained in this expansion message in total, the second "1" is the number of this packet in the sequence, and the "A" may be some further indcator of type of message.

The code 3380400790 is the marine mobile service identity of the station sending the data, with a zero appended.

The code 00 is unknown to me.

The code 46504437 appears to contain the decimal minutes of the latitude and longitude in the other packet. The 4560 is the decimal minutes of longitude to 0.0001, and the 4437 is the decimal minutes of longitude to 0.0001, both to a ten-thousandths of a minute.

The code *15 appears to be a check sum to allow the packet to be checked for accuracy by parsing of all the elements.
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Old 22-04-2014, 05:53   #3
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Re: NMEA-0183 Sentences DSC, DSE

Oops--In the above I left out part of the DSC message, following the $CDDSC:

The 20 is probably an indicator of the type of message that follows.

Also, the "1" that is sent before the latitude may be an indicator of the N/S and E/W nature of the position, perhaps according to

0=N,E
1=N,W
2=S,E
3=S,W
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Old 14-02-2017, 09:48   #4
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Re: NMEA-0183 Sentences DSC, DSE

UPDATE:

Since posting this article about my early inquiries into the DSC and DSE sentences, I have conducted some experiments with Class-D DSC radios and analyzed the data-link output they produce. The outcome of this experiment has been the formulation of a general inference about the structure of the NMEA DSC and DSE sentences.

I describe in detail the experiments I conducted, the inferences I was able to make from their results, and my general conclusion about the structure of NMEA sentences DSC and DSE in the third article of my four-part series on DSC radio behavior. See

Data Interface in Digital Selective Calling Class-D Radios
continuousWave: Whaler: Reference: Data Interface in Digital Selective Calling Class-D Radios
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