[time-nuts] Short term 10MHz source

[Tom Van Baak]

> Use the Rb as your reference and log the time offset of its PPS.
> Manually steer vs a 10 hour GPS PPS data set once a week.
> You probably will stretch it out to a couple weeks after things settle in.

I'm with Bob here. Once a week, once a month, once a year, even once a lifetime: the choice depends on your accuracy requirements. For example, you can easily obtain ppb-levels (9 digits of accuracy) from an Rb with only once a year adjustment.

If you need to generate precise 10 MHz for some sort of transmitter or real-time customer then, yes, you should use a GPSDO -- a h/w solution to steering. But if all you are doing is making precise measurements and collecting data then a s/w solution is applicable. Consider it "data steering". You don't need EFC or Vref or DAC or other complexities of a GPSDO.

I do lots of multi-channel TAPR/TICC, TIC, picPET logging here. I rarely use an actual GPSDO. Instead I just log a GPS/1PPS as one of the counter(s) channel(s). That way you never have to calibrate your timebase, regardless if it's XO or OCXO or Rb. The timebase just free-runs. The calibration is done in s/w when you later process your counter readings. By recording a GPS tick along with all your DUT(s) you get tracking and calibration of your LO for free.

The TICC is designed to do this. It's not just a 2-input start/stop TIC, but a dual / independent timestamping counter.

This is similar to the trick people do with sound cards. Put a 1PPS into the R-channel and your signal into the L-channel. The inaccuracy and instability of the PC clock, or NTP, or RTC, or sound card xtal, or USB latency all drop out. It's a self-calibrating system.

/tvb