[time-nuts] Mains frequency

[Tom Van Baak]

> There is no way to come up with the noise floor of the picPET from that plot.

Hi Bob,

The goal of the red trace was to see if a fancy hp 33120A would give better or worse or same performance as mains 60 Hz. This simple substitution technique is a quick way to check if mains or the picPET might be the limiting factor. The slope and intercept suggests the picPET has resolution of at least 1e-6/tau. I say "at least" because we don't know how much of that is due to the 33120A.

Notice that for tau greater than about 1/3 second, picPET (and REF) instability is significantly below mains (DUT) instability. For tau 0.01 to 0.3 s it would take more work to quantify which pieces are contributing to the instability pie.

Attached is an ADEV plot; this one includes the past two weeks, and also a 100 day continuous run from Feb/Mar/Apr/May 2012. The GPSDO-like steering of mains frequency is visible in this trace.

You also might be wondering why the red trace hits a floor and drifts up. That's due to the TCXO in the 33120A. The reference for the picPET was one of those cute 10 MHz Micro-Crystal DIP OCXO, which easily outperforms the TCXO.

/tvb
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