If you're familiar with the older NMEA 0183, there was a "GSV" record for reporting information about GPS satellites in view, including their SNR (signal-to-noise ratio, also known as carrier-to-noise-density ratio, C/N0), though only as an integer value (between 0 and 99, nominally in decibels, often in dB-Hz). a,b,c

Did this situation change in the newer NMEA 2000? There is a similar message 129540 about "GNSS Sats in View", but the free N2K Field Descriptions does not specify the fields data types:

GNSS information on current satellites in view tagged by sequence ID. Information includes PRN, elevation, azimuth, SNR, defines the number of satellites; defines the satellite number and the information.

I found an official white paper which gives an example for a similar SNR field but for Loran stations instead of GPS satellites, which says:

Data type: int16; Range: +/-327.5 dB; Resolution: 0.01 dB

Does anyone with knowledge of the specification confirm that what applies to message 130054 ("Loran-C Signal Data") is also applicable to message 129540 ("GNSS Sats in View")? Searching further I found some software documentation suggesting that it does:docs

PGN: 129540 - GNSS Sats in View (...) Field #8: SNR Bits: 16 Units: dB Resolution: 0.01 Signed: false

So now the final question is: do real receivers make use of the extra resolution available? Could anyone with access to a GPS/GNSS unit supporting NMEA 2000 provide a text sample of that message output, please? I heard that some of latest Garmins and Hemisphere receivers work that way.

I have a scientific application that requires SNR values more precise than 1 dB, see Scientific Utility of the Signal-to-Noise Ratio (SNR) Reported by GPS Receivers.

1 Answer 1


Gamin technical support has said:

I can confirm that the 19x NMEA 2000 antenna does use the full 0.01dB resolution in "GNSS Sats in View" mode.

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