NMEA-0183 Data for DSC Radio

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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Location: Michigan, Lower Peninsula
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NMEA-0183 Data for DSC Radio

Postby jimh » Tue Dec 11, 2018 12:06 pm

Most digital selective calling (DSC) VHF Marine Band radios are interfaced using NMEA-0183 to a source of digital data that provides automatic position updates. There are several NMEA-0183 sentences that can be used to send data to the radio. This article discusses the content of those sentences and which is most useful.

GGA—Fix Information
The GGA sentence will contain the following data:
  1. Time (UTC)
  2. Latitude
  3. N or S (North or South)
  4. Longitude
  5. E or W (East or West)
  6. GPS Quality Indicator
    1. 0 - fix not available,
    2. 1 - GPS fix,
    3. 2 - Differential GPS fix
  7. Number of satellites in view, 00 - 12
  8. Horizontal Dilution of precision
  9. Antenna Altitude above/below mean-sea-level (geoid)
  10. Units of antenna altitude, meters
  11. Geoidal separation, the difference between the WGS-84 earth ellipsoid and mean-sea-level (geoid), "-" means mean-sea-level below ellipsoid
  12. Units of geoidal separation, meters
  13. Age of differential GPS data, time in seconds since last SC104 type 1 or 9 update, null field when DGPS is not used
  14. Differential reference station ID, 0000-1023
  15. Checksum

Not every GPS receiver will send all fields of GGA. A typical receiver might send only TIme, Latitude, Longitude, Altitude, HDOP, and number of satellites in view. The GGA sentence is very useful for a radio DSC position fix update.

jimh
Posts: 6463
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: NMEA-0183 Data for DSC Radio

Postby jimh » Tue Dec 11, 2018 2:27 pm

Another NMEA-0183 sentence that could be used is GLL. This is a very simple sentence.

GLL Geographic Position – Latitude/Longitude
The GLL sentence will contain the following data:
  1. Latitude
  2. N or S (North or South)
  3. Longitude
  4. E or W (East or West)
  5. Time (UTC)
  6. Status A - Data Valid, V - Data Invalid
  7. Checksum