[time-nuts] Re: GPSDO/GNSSDO project: STM32G4 + u-blox ZED-F9T + TDC7200

[Carsten Andrich]

Hi Bill, John, Greg, Uwe,

thanks for chiming in.


On 06.08.22 20:29, John Ackermann N8UR via time-nuts wrote:
> I believe that the "T" models can output RTCM data so can serve as an 
> RTK base station, but only the "P" models have the built-engine to 
> receive corrections via UART or USB and do RTK internally.  So without 
> that, I don't see how you can get corrected time directly from the module.

While the F9T does not support RTK positioning, it does apparently 
utilize the code and carrier phase correction information part of RTK 
correction data (RTCM 10403.*) to improve timing accuracy, e.g., by 
eliminating atmospheric distortion.


On 07.08.22 02:03, Greg Troxel via time-nuts wrote:
> Can anyone explain a mechanism for the positions getting better but time
> either getting worse or not changing?

On 07.08.22 05:47, Uwe via time-nuts wrote:
> SBAS is disabled by default for timing applications using F9T.

u-blox advise against the use of SBAS for timing [1, 2], because:

> [...] theadditional inter-standard time calibration step used during 
> SBAS reception results in degraded timeaccuracy overall.


On 07.08.22 05:47, Uwe via time-nuts wrote:
> RTK corrections works only from F9T to F9T.
> you need RTCM 7 ( MSM 7) messages. (RTCM 1077 and more)
> [...]
> You will need one F9T Base sending RTCM 7 massages. The Base works as NTRIP caster .
> The NTRIP client F9T reseive RTCM 7 data for finding position. The Time Mode of F9T works only if the client not moving.

That's my plan. One stationary F9T operating in time mode (surveyed, 
fixed position; 1D timing solutions) sending MSM7s to the mobile receivers.

Best regards,
Carsten


[1] 
https://content.u-blox.com/sites/default/files/ZED-F9T-00B_DataSheet_UBX-18053713.pdf#page=6
[2] 
https://content.u-blox.com/sites/default/files/ZED-F9T_IntegrationManual_UBX-21040375.pdf#page=23