[time-nuts] A simple sampling DMTD

Tue Feb 25 02:37:24 UTC 2020

It turns out Bobs dumpster was my dumpster by a long path.
I still have the sampling HP54100 1 Ghz scope and it works.
Many other lucky bits to get.
Best regards
Paul
WB8TSL

On Mon, Feb 24, 2020 at 1:43 PM Bob kb8tq via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi
>
> Yup, welcome to the online auction lottery ….. As you may have noted, I’m
> struggling a bit with the Phase Station and random (likely my fault)
> issues.
>
> At the same time, I’m going around in circles about the R&S FPC-COM2. It’s
> a pile of money, but it would replace a lot of questionable gear I have
> sitting
> here. Most of what I have was quite literally pulled from / saved from the
> dumpster at various points over the last few decades …..
>
> Bob
>
> > On Feb 24, 2020, at 12:33 PM, Taka Kamiya via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> > I woke up this morning, check my HP105B, it's absolutely going nuts.
> Heater temp down, frequency ALL OVER the place.  No output in any of the
> ports.  Sigh.....  eBay strikes again!
> >
> > ---------------------------------------
> > (Mr.) Taka Kamiya
> > KB4EMF / ex JF2DKG
> >
> >
> >    On Sunday, February 23, 2020, 7:52:02 PM EST, Bob kb8tq via time-nuts
> <time-nuts at lists.febo.com> 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 <jdbakker at 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 <kb8tq at n1k.org <mailto:
> kb8tq at 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 at lists.febo.com <mailto:time-nuts at 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 at lists.febo.com <mailto:time-nuts at 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 <jdbakker at gmail.com <mailto:jdbakker at 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 at tau=1s versus 3.25e-13 at 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.
> >>>>
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