[time-nuts] Re: Ublox ZED-F9T - group delay

[Zdenek Chaloupka]

Hi Fred,

there are three things to consider:

1) alignment of the 1PPS from your GNSS simulator to the simulator’s RF output. GNSS simulators are typically aligned to L1 C/A signal with different  level of accuracy.
2) 1PPS cable delays, and 1PPS measurement threshold - those can influence your absolute 1PPS offset from GNSS simulator.
3) ZED-F9T module carrier board. I am assuming you have ZED-F9T module soldered on something. Even though ZED-F9T may have been calibrated in production, as soon as it undergoes solder heating cycle, this can easily shift the group delay of internal components of ZED-F9T.

I think best way to go around this is to calibrate 1PPS output against good GNSS simulator after the ZED-F9T is soldered on the PCB. No more solder heat cycles after calibration!

Best regards
Zdenek


> On 29 Apr 2024, at 11:36, rf lab via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi All,
> 
> I have a ublox ZED-F9T with a very short RF trace to an SMA connector (<
> 1cm), so I expect the delay due to the RF line to be in the ~100's pico sec
> range.  Using a GNSS simulator I measure the average 1pps delay relative to
> the simulator to be about 25ns.  This figure is quite close to a typical
> GNSS SAW group delay.
> 
> My question is if anyone has done something similar or knows what the
> actual delay is for a ZED-F9T module.
> 
> Thanks
> Fred
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