[time-nuts] Mains frequency

[Bob Camp]

Hi

I spent a lot of time with a sine wave input on this sort of stuff… You can come up with a line that the floor must be below. Find a better source and that line moves down. You can’t find the actual floor. You can only establish that it must be below this or that level. It’s not like the noise floor of a radio….

Bob

On Nov 19, 2013, at 6:06 AM, Tom Van Baak <tvb at LeapSecond.com> wrote:

>> 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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