Does my RINEX file have carrier data in it?

Background:  Without both code and carrier data, RTK and PPP navigation methods are not possible.  While it is routine to have both (as well as other signals) in better modules and chips, some very low end chip sets do not provide a carrier output.  This basically kills any ability to use such a chip set for RTK or PPP style navigation.  Avoid them if you need sub-meter accuracy. If you look at the RINEX files for any system you can easily tell if carrier data is present.

Hint:  RINEX, or the Receiver Independent Exchange Format,is the preferred human readable data interchange format used to exchange various types of GNSS measurements.

The carrier field in any RINEX file is the “L” (as in L1 or L2 etc.), if you do not see that field in the file header then you do not have carrier data.  The code (pseudorange) is the C, Doppler is D (not found in all systems) and S is the SNR (C over No).  Most converter tools have some options to suppress unused fields, so check to make sure the convert step did not removed the carrier data by mistake.

Below is a fragment from  a uBlox 6T (an L1 only device) for one epoch (one measurement set).

The first 4 lines are part of the file header and serve to lay out the format of the data to follow in the file (this is fixed for the entire file). The next line is the time stamp of the measurement epoch (accurate to ~100nS). It also tells us that 12 more lines will follow for the 12 SVs that have measurements at that time and then enumerates the order of the SVs (which can change with each measurement epoch).  This is a version 2 file style; version 3 differs in some ways.

There is code, carrier, Doppler and and SNR for all of these measurements but for one.   You can see that the carrier for SV “G20” was missing in this data set. The RINEX format allows blank spaces to stand in for zeros.  FYI about this SV:  One can also see that this SV was low on the horizon and dropping out of view as the high negative Doppler rate and low SNR shows, which is the typical time carrier tracking is lost.

RINEX Fragment

      4    C1    L1    D1    S1                              # / TYPES OF OBSERV 
   2016     6     7    17    42   46.0000781     GPS         TIME OF FIRST OBS   
   2016     6     7    18     3   27.0000781     GPS         TIME OF LAST OBS    
                                                             END OF HEADER       
  16  6  7 17 42 46.0000781  0 12G 7G 8G26G20G21G15G16G27G18G10S20G 4
   24315075.481   127776517.3292        448.410          29.000  
   22629267.575   118917537.1101       2271.698          32.000  
   21895722.936   115062756.905       -3156.582          42.000  
   25179786.705                       -3549.886          20.000  
   23308387.593   122486312.002       -2759.055          46.000  
   25514482.824   134079506.961         333.453          33.000  
   20601440.208   108261249.8101      -1454.798          43.000  
   20620768.706   108362926.6981        797.603          40.000  
   22056801.307   115909274.4371       -833.425          46.000  
   21617601.357   113601266.278        1698.172          47.000  
   37871568.996   199016439.7911       -286.053          29.000  
   23186586.975   121846252.716       -3871.296          40.000  

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