NavCom Sapphire Rev.J - Manual (Page 299)

Sapphire Technical Reference Manual Rev. J
299
2.55 NMEA Messages Overview
SF-3050 Sapphire SF-3040
Selected sentences included in the ensuing sections are defined in the National Marine
Electronics Association (NMEA) document 0183 “Standard For Interfacing Marine Electronic
Devices”, Version 3.01, January 1, 2002 or up to v.3.0.13 of the software. Subsequent software
versions support NMEA 0183, v.4.1. A software “switch” is available to return NMEA data to the
former standard version.
These messages are all prefixed with the string value “NMEA”, and can be viewed as a
common set of sentences describing navigation data.
The NMEA sentences describe mechanics for GPS, GLONASS and WAAS satellites. To
differentiate them, NMEA defines the following naming convention for satellite ids:
1. GPS satellites are identified by their PRN numbers, which range from 1 to 32.
2. The numbers 33-64 are reserved for WAAS satellites. The WAAS system PRN numbers
are 120-138. The offset from NMEA WAAS SV ID to WAAS PRN number is 87. A WAAS
PRN number of 120 minus 87 yields the SV ID of 33. The addition of 87 to the SV ID
yields the WAAS PRN number.
3. The numbers 65-96 are reserved for GLONASS satellites. GLONASS satellites are
identified by “64 + satellite slot number”. The slot numbers are 1 through 24 for the full
GLONASS constellation, giving a range of 65 through 88. The numbers 89 through 96
are available if slot numbers above 24 are allocated to on-orbit spares.
The NMEA sentences describe the satellite population using the following naming convention:
$GPxxx, describes data generated from GPS satellites only
$GLxxx, describes data generated from GLONASS satellites only
$GNxxx, describes data generated from mixed GPS and GLONASS satellites