After building a phase comparator using a 7474 and a 7400 it became possible to observe every second the phase delta between the PPS and the 2.5MHz clock on a DSO
The maximum phase comparator pulse duration is 400ns (2.5MHz clock) , minimum is zero.?
The TCXO seems to be very stable. When the arduino SW is "in lock" you see the phase drift slowly depending on the remaining frequency error.
With an error of 1e-8 the phase changes with 10ns every second but when in lock the shift per second is much less then 10ns.
A possible problem is the corrections to the PPS being made which cause a phase jump of 20ns. Not sure yet how to deal with these jumps. Probably some form of intelligent averaging will be required
Using the pulse duration to voltage translator as used in Lars GPDSO it should be possible to observe the phase changes by the arduino SW every second and use these phase changes over a certain time duration to correct the SI5351 more often then when using the 400s or more pulse measurement time.
A clear disadvantage of the SI5351 (instead of using a true VCXO) is loosing the phase after each frequency update so you have to restart the phase measurement after each frequency update.
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HBTE Files section:?
/g/HBTE/filesErik, PD0EK
