[time-nuts] ublox gnss receiver data

[Luiz Paulo Damaceno]

Hi all!

I'm testing ublox's ZED-F9T GNSS receiver for time transfer applications
and i've observed few things at data processing. This receiver is being
feed with external 49.58 MHz coming from a synthesizer that is locked to
Symmetricom's 5071A cesium frequency standard since we've removed its TCXO
to make the time transfer tests.

For the tests, I've processed .ubx raw data, then RINEX 3.04 data with
RTKCONV present at RTKLib software. After that,  I was able to see the
following RINEX observation types:

G    4 C1C L1C C2X L2X                                      SYS / # / OBS
TYPES
R    4 C1C L1C C2C L2C                                      SYS / # / OBS
TYPES
E    4 C1X L1X C7X L7X                                      SYS / # / OBS
TYPES
C    4 C2I L2I C7I L7I                                      SYS / # / OBS
TYPES

The main question is: why L2 data for GPS is classified by "X" for code and
phase?
I've tried to process it with NRCAN's PPP software, but only had success
when changed "C2X" and "L2X" to C2C and L2C.

Now... Other things that I cannot explain and occurred:

1 - For the case that i've not changed X for C, i cannot process CGGTTS
data for L2C frequency for GPS constellation. Only L1C clock data.
2 - For GLONASS and BeiDou constellation, without any changings in the
observation types I can see L3P clock data, with coherent MDIO and MSIO
values I guess...
3 - After changing GPS observation types for C2C and L2C, I have two files:
L1C clock data and L2C clock data.
4 - After changing GPS observation types for C2P and L2C, i was able to
have CGGTTS L3P data for GPS Constellation, but i guess that data is not
valid because the receiver is not receiving "P" code in any frequency, even
if use biasC1P1 file, the data shouldn't be real, right? So... Why is MDIO
and MSIO also valid?
5 - I can see only GALILEO's E5b data, and L1 data seems to be not
available.

I've uploaded a few files to you to see some results in those files. I'm
using the r2cggtts program and the input files are "rinex_nav_mix" and
"rinex_obs".

Link for the files: Google Drive
<https://drive.google.com/drive/folders/115TAVbOOMkpxXbt4JLnR94nODbRFEgys>

For the files, -rp2 means that i've changed original observation data
(258_ubx.obs) from L2X to L2P type, also C2X to C2P type. For that, my
question is: why GLONASS and BeiDou, even having an "P" code on the
receiver, are able to generate L3P data? Rember: I've only changed X to P
observation type for GPS constellation, everything else remains untouched.

If you have links and other sources with works related to this I will
appreciate it! Thanks.

Best regards,

Luiz