Hi There is no way to come up with the noise floor of the picPET from that plot. In fact coming up with the floor of a single channel device like the picPET is not all that easy. First you need an ideal noise free sine wave signal …. I’ve spent more than a few hours on that particular project with other list members involved as well. As always we kept it off list to keep from offending those who place a high value on their bandwidth.
Bob On Nov 18, 2013, at 9:11 PM, Bill Dailey <docdai...@gmail.com> wrote: > I meant ideal at the noise floor of the picPET (i.e in this case the > generated 60Hz). > > > On Mon, Nov 18, 2013 at 8:08 PM, Bob Camp <li...@rtty.us> wrote: > >> Hi >> >> An “ideal” curve would go to the bottom of the scale as soon as the plot >> started. Anything that shows on the ADEV curve is by definition noise. The >> slope of the ADEV curve can help you determine what sort of noise it is. >> The slope(s) on an modified ADEV curve can do that slightly better. >> >> Bob >> >> On Nov 18, 2013, at 8:03 PM, Bill Dailey <docdai...@gmail.com> wrote: >> >>> tom, >>> >>> nice plots. how do you figure out what the contribution of variability >> vs >>> noise? In other words there is a differential between the "ideal" and the >>> actual a dev curves... is there a way to tease out how much nose >> contribute >>> to that differential? It does seem to me that there should be far less >>> short term variability (< 100s) than there appears to be. Clearly in the >>> very short tau (< 0.1 s) the picPET can't tease that out but as the >> curves >>> diverge, how much of that is noise? between say 0.1s and 100s? Being a >>> power plant operator I would say quite a bit although I am rethinking >> that >>> some due to the way the turbines push and pull each other. I can >> envision >>> some fine whole grid oscillations due to that push and pull. >>> >>> bill >>> >>> >>> On Mon, Nov 18, 2013 at 4:15 PM, Tom Van Baak <t...@leapsecond.com> >> wrote: >>> >>>> Magnus, >>>> >>>> I'm going to push back a bit on your mains sampling claim. Mostly, I'd >>>> like to see the results of the professional I-Q demodulated gear that >> you >>>> mentioned. Can you post raw data, or a sample plot? >>>> >>>> I agree that looking at power line voltage with 16- or 24-bits at 1 Msps >>>> is going to reveal interesting amplitude and phase noise information. >> But >>>> see how well a $1 PIC can do. >>>> >>>> Attached is a plot made using TimeLab + picPET just now. The picPET is >>>> fast enough to capture the zero-crossing of every 60 Hz cycle with 400 >> ns >>>> resolution; the TimeLab plots have tau0 of 16.67 ms. >>>> >>>> -- The blue trace was simply plugging a 9 VAC wall-wart into the picPET >>>> though a 10k resistor. >>>> -- The pink trace was adding a 10 nF cap across the input. >>>> -- The green trace was unplugging my laptop switching power supply from >>>> the same outlet! >>>> -- The red trace is replacing the mains wall-wart with a hp 33120A set >> to >>>> 9VAC at 60 Hz, a tentative noise floor measurement of the picPET when >> used >>>> this way. >>>> >>>> My conclusions are that at least here in the US, or at least at my >> house, >>>> the short-term stability of mains hits about 5e-6, at about tau 0.2 >>>> seconds. The attached short-term plot is also not-inconsistent with the >>>> long-term plot at http://leapsecond.com/pages/mains/ >>>> >>>> My other conclusion is that the picPET (a simple PIC-based time-stamping >>>> counter) is doing a pretty good job measuring this. Note, no software or >>>> data filtering was used. This is just raw serial/USB data going into >>>> TimeLab. >>>> >>>> /tvb >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> >>> >>> >>> -- >>> Doc >>> >>> Bill Dailey >>> KXØO >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > -- > Doc > > Bill Dailey > KXØO > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.