Hi …… looking at the data this morning. It appears that in my case *somebody* (I’m blaming the dog) must have bumped the setup. There is a very obvious set of steps in the phase data. The overnight run has no similar steps. Sometimes getting everything away from the test is a good thing …..
Bob > On Feb 23, 2020, at 7:51 PM, Bob kb8tq <kb...@n1k.org> wrote: > > Hi > > Ok, but thats “high pass in the RF section”. You really do not have an audio > high pass > filter the way you would in a more typical DMTD. > > If it’s any comfort, I’m sitting here looking at a very different box. It > also has “wobbles” > as you get into parts in 10^-16. That might change a bit if the draft coming > through the > window was a bit less. > > Bob > >> On Feb 23, 2020, at 6:12 PM, Jan-Derk Bakker <jdbak...@gmail.com >> <mailto:jdbak...@gmail.com>> wrote: >> >> Dear Bob, >> >> The capacitors are 47n NP0/C0G types (Kemet C0805C473K3GAC7800), picked for >> low tempco (and low DF and other non-ideal behavior). I've not spotted any >> hysteresis artefacts in these in previous designs, but I haven't measured >> their performance in this circuit. >> >> Forgot to mention in the previous message: the baluns are transformers >> (M/A-COM MABAES0060), so the only DC the ADC should see is its own input >> offset (plus offset current across the 25R input filter resistors). Full >> schematic is here ( http://www.lartmaker.nl/time-nuts/DMTD_rev0.99.pdf >> <http://www.lartmaker.nl/time-nuts/DMTD_rev0.99.pdf> ; needs cleanup, but >> all connections are there). >> >> JDB. >> >> On Sun, Feb 23, 2020 at 10:13 PM Bob kb8tq <kb...@n1k.org >> <mailto:kb...@n1k.org>> wrote: >> Hi >> >> What does the temperature coefficient of your “hardware HPF” filter caps >> look like? >> Are they a type that has significant hysteresis? >> >> Bob >> >> > On Feb 23, 2020, at 3:05 PM, Jan-Derk Bakker via time-nuts >> > <time-nuts@lists.febo.com <mailto:time-nuts@lists.febo.com>> wrote: >> > >> > Dear Attila, >> > >> > Thanks for the heads up. >> > >> > I am currently using a HPF both in hardware (capacitive coupling into the >> > balun driving the ADC inputs) and in software before the ZCD. This should >> > counteract the first-order effects of this offset, although second-order >> > effects (converter nonlinearity et al) will of course still be an issue. >> > The plots you've quoted include (different kinds of) DC offset correction >> > for all but the "unfiltered" data; getting an efficient DC offset >> > correction working in real time on this 8-bit platform was indeed one of >> > the main challenges of the software-only approach. >> > >> > The FPGA daughterboard is currently in production at Eurocircuits; I hope >> > to have time to work on those the coming month. I'll also try to book some >> > time in our climate chamber. (I've had one of our GPSDO-designs running in >> > our general labs since before Christmas; surrounding it with bottles of >> > water works well enough to low pass filter temperature swings, but I still >> > see 6 degrees C swings overnight as out HVAC only runs during business >> > hours.) >> > >> > To be continued, >> > >> > JDB. >> > >> > On Sun, Feb 23, 2020 at 8:11 PM Attila Kinali via time-nuts < >> > time-nuts@lists.febo.com <mailto:time-nuts@lists.febo.com>> wrote: >> > >> >> Good evening! >> >> >> >> I'm going through some old stuff... >> >> >> >> >> >> On Wed, 27 Nov 2019 00:29:19 +0100 >> >> Jan-Derk Bakker <jdbak...@gmail.com <mailto:jdbak...@gmail.com>> wrote: >> >> >> >>> This has yielded a combined "simple" signal >> >>> processing path of a differentiator, a double comb filter and the offset >> >>> estimator, which is getting very close in performance to the "ideal" band >> >>> pass filter (OADEV of 3.77e-13@tau=1s versus 3.25e-13@tau=1s for the >> >> BPF; >> >>> full plot: >> >>> >> >> http://www.lartmaker.nl/time-nuts/DMTD%20self-noise%20OADEV%20with%20PLL%20and%20various%20filters.pdf >> >> >> >> <http://www.lartmaker.nl/time-nuts/DMTD%20self-noise%20OADEV%20with%20PLL%20and%20various%20filters.pdf> >> >>> for this 600000-second recording: >> >>> >> >> http://www.lartmaker.nl/time-nuts/600ksec%20run%20with%20PLL,%2010811%20through%20splitter.png >> >> >> >> <http://www.lartmaker.nl/time-nuts/600ksec%20run%20with%20PLL,%2010811%20through%20splitter.png> >> >>> . OADEV past ~1000sec is severely compromised by the fact that the >> >>> measurement setup is in my home lab which sees temperature swings of up >> >> to >> >>> 20 degrees C and which does get bumped from time to time. Longer runs in >> >> a >> >>> more controlled setting forthcoming). >> >> >> >> >> >> I can offer an explanation for the large effect of the zero correction >> >> seen >> >> here. The LTC2140 is specified to have a +/-10µV/°C drift (at 1Vpp >> >> setting). >> >> Converted into phase error due to zero crossing shift, this turns into >> >> a phase shift of +/-1ps/°C @ 10MHz. Note, the shift is given as +/- and >> >> per channel, which means, it could very well be that the channels are >> >> not matched in their temperature characteristics and thus the total phase >> >> shift could be +/-2ps/°C ... though total shift being closer to 0.5ps/°C >> >> is >> >> more likely. >> >> >> >> Summa sumarum: DC offset correction is important if a zero crossing >> >> detector is used. >> >> >> >> Attila Kinali >> >> >> >> -- >> >> <JaberWorky> The bad part of Zurich is where the degenerates >> >> throw DARK chocolate at you. >> >> >> >> _______________________________________________ >> >> time-nuts mailing list -- time-nuts@lists.febo.com >> >> <mailto:time-nuts@lists.febo.com> >> >> To unsubscribe, go to >> >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> >> <http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com> >> >> and follow the instructions there. >> >> >> > _______________________________________________ >> > time-nuts mailing list -- time-nuts@lists.febo.com >> > <mailto:time-nuts@lists.febo.com> >> > To unsubscribe, go to >> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> > <http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com> >> > and follow the instructions there. >> > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.