Re: [time-nuts] Phase Detectors/Mixers for DMTD and PN measurements

[Bruce Griffiths]

There are a number of NIST papers on this:
https://tf.nist.gov/general/publications.htm

You can also simulate the effect of a capacitive IF port load.
However a capacitive load can also degrade the isolation and RF and LO port 
mismatch.

One can also use diode connected BJTs instead if lower close in PN is desired 
at least for frequencies up to 10MHz or so.
There is a NIST paper on this as well:
https://tf.nist.gov/general/pdf/2556.pdf

Bruce

> On 11 December 2019 at 22:55 Tobias Pluess  wrote:
> 
> 
> Hi colleagues
> 
> In parallel to my GPSDO project I am also thinking about a DMTD measurement 
> system which should also be capable of doing phase noise measurements. This 
> will be necessary to measure the stability and phase noise of my own GPSDO.
> 
> There is the paper from W. J. Riley, "A small DMTD system". He uses TUF-R3SM+ 
> mixers. The HP 11729C carrier noise test set uses a custom HP part as phase 
> detector, and a lot of other publications I found use the HP 10514A, either 
> as mixer or as phase detector.
> I wonder, which criteria are relevant to select a mixer for this application 
> (besides the frequency range). Are there devices which are better when used 
> as mixers, or phase detectors, or are there even devices which are good for 
> both purposes? Of course, we want low noise, but for most if not all 
> commercial mixers, only the isolation and conversion loss is specified, but I 
> never saw a mixer datasheet having information about the mixer's noise 
> contribution. So there must be other criteria people use when selecting a 
> mixer for a DMTD or phase noise measurement system.
> 
> Further. in this paper "OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE 
> MULTIPLIER" from Sojdr I even found a reference "The mixer output has a 
> capacitive loading (22 nF) that increases the zero-crossing slope". The 
> "Small DMTD system" from Riley also does have this capacitive loading. Can 
> somebody explain why this does help to improve the zero crossing slope?
> 
> 
> Tobias
> HB9FSX
> 
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Re: [time-nuts] Phase Detectors/Mixers for DMTD and PN measurements

[Bruce Griffiths]

Cross Correlation methods are commonly used with analog mixers.
Most of the high end commercial offerings use it (Holzworth, Anapico, Rhohde & 
Schwarz, etc.)

Bruce
> On 12 December 2019 at 18:53 Gerhard Hoffmann  
> wrote:
> 
> 
> It seems the mixer noise cannot be ignored.
> 
> 
> I wonder then  why nobody  takes the mixer to cross correlation land, 
> and maybe even the driver amplifier.
> 
> The FFT analyzer can do it anyway, a second AF pre amp costs nothing,  
> and other than that
> 
> there are only another mixer and 2 power dividers on the BOM.
> 
> In addition, each mixer gets 3 dB less power which helps the survival rate.
> 
> One can always crank it up for bragging rights.
> 
> 
> Also, high level mixers (type 2 and 3 in [1] ) have resistors in series 
> to each diode for biasing
> 
> so their lower efficiency should not come as a surprise.  And, the 
> resistors in the ring generate
> 
> AF noise. With DC across them also 1/f, esp. for thick film.
> 
> The usual 1nV/rt Hz op amps (LT1028, AD797, ADA4898) have the voltage 
> noise of a 60 Ohm resistor.
> 
> That probably brings them to the point of diminishing return.
> 
> The diodes in the ring themselves create only half-thermal noise.
> 
> 
> Methinks one would be better off with many low level mixers and power 
> dividers,
> 
> adding up the demodulated AF voltages. There is no point in power 
> matching the AF side.
> 
> Maybe for RF with a RC high pass.
> 
> SMD Wilkinson dividers are $2.50 or so now from Macom, MCL or Pulse and
> 
> low level mixers are also cheap, or even 2 1:4 SMD transformers + diode 
> ring.
> 
> Easily done when one does not have to wind the coils.
> 
> 
> When verifying my links below, I stumbled across M9H  for $333.
> 
> The price for two of them is the number of the beast.  =8-) )
> 
> 
> [1]
> 
> < 
> https://www.jlab.org/uspas11/Reading/RF/Mixers%20-%20phase%20detectors.pdf >
> 
> 
> < 
> https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiu8Zi7pa_mAhUKQUEAHb1pAyAQFjAAegQIAxAJ&url=http%3A%2F%2Fwww.rfcafe.com%2Freferences%2Farticles%2Fwj-tech-notes%2Fmixers-theory-technology-p2-v8-3.pdf&usg=AOvVaw3fc3OZgN2H5jzPx6jXDBh9
>  
>     >
> 
> 
> Also interesting:
> 
> < 
> https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwiFuqCvpq_mAhVTh1wKHcc2ALQQFjAAegQIAxAJ&url=http%3A%2F%2Fliterature.cdn.keysight.com%2Flitweb%2Fpdf%2F5989-8999EN.pdf&usg=AOvVaw3RFawCNg543QEv1hUsscbY
>  
>    >
> 
> 
> regards,
> 
> Gerhard,  DK4XP
> 
> 
> 
> 
> Am 11.12.19 um 20:29 schrieb Bob kb8tq:
> > Hi
> >
> > There are some famous name papers showing data taken on the 3048. When
> > asked about the levels involved, the next question inevitably was - “How 
> > many
> > mixers did you fry running the test?”.
> >
> > Bob
> >
> >> On Dec 11, 2019, at 10:54 AM, Richard (Rick) Karlquist 
> >>  wrote:
> >>
> >>
> >> The HP 3048A phase noise system has a phase
> >> detector in the HP 11848A chassis that was
> >> originally a Watkins-Johnson (the original
> >> company) M9H.  The M9H lives on now sold by
> >> MaCom Technology Solutions.  "Someone" (unknown)
> >> established that the Mini-Circuits JMS-5H
> >> is an acceptable substitute, although not
> >> an exact replacement.
> >>
> >> The tradeoff in picking a mixer is the LO
> >> level.  A high LO drive level such as the above
> >> mixer have, gives higher performance, provided
> >> you have a driving amplifier that has both the
> >> necessary output power is itself low phase noise.
> >> Depending on the test set up, some of the driver
> >> amplifier phase noise will common mode out.
> >>
> >> Also, high drive level mixers have a narrow window
> >> between high enough drive to operate vs the damage
> >> level.  So a third requirement on the driver
> >> amplifier is that it's maximum output level is
> >> less than the damage level.  (Don't ask how I
> >> know this :-).  You can always put a pad between the
> >> drive amplifier and the LO input of the mixer used
> >> as phase detector to adjust the maximum possible
> >> drive.
> >>
> >> Rick N6RK
> >>
> 
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Re: [time-nuts] low phase noise, noise floor and noise figure amplifier at 400MHz

[Bruce Griffiths]

That's not possible at room temperature since thermal noise will limit the 
residual PN to -180DbC/Hz with a noiseless amplifier and a +3dBm input.

Bruce

> On 10 January 2020 at 14:38 Lifespeed  wrote:
> 
> 
> Hi Time Nuts,
> 
>  
> 
> I have a need for a low phase noise, noise floor and noise figure amplifier
> at 400MHz.  I have tried some off-the-shelf 50 ohm amplifiers, the best of
> which degrades phase noise by a couple dB.  I'm working with a signal with
> -172dBc/Hz PN, so not much tolerance for degradation here.  The input signal
> level is only 3dBm, so noise figure still matters as well.  I'm looking for
> 15dB gain, 16dBm P1.  The residual phase noise would have to be better than
> -180dBc/Hz, and I would probably operate the amplifier slightly compressed.
> 
>  
> 
> Any suggestions on topologies, transistors, white papers, etc?  I'm
> considering the NXP BFU590Q silicon bipolar transistor, which I have used in
> a transformer feedback configuration at 100MHz with less than -180dBc/Hz PN.
> But this topology doesn't appear practical for 400MHz due to the difficulty
> maintaining a high collector impedance at that frequency with a transformer.
> Nor do I need to control the gain, which is one of the features of the
> transformer-feedback topology.  I was thinking about common emitter with
> inductive emitter degeneration.  Not sure cascode is right for this UHF
> application.
> 
>  
> 
> Lifespeed
> 
>  
> 
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Re: [time-nuts] low phase noise, noise floor and noise figure amplifier at 400MHz

[Bruce Griffiths]

The phase noise specifications for an amplifier are meaningless if the input 
signal level isnt specified.
Bruce
> On 11 January 2020 at 03:27 Leon Pavlovic  wrote:
> 
> 
> The HP K22 had a specified noise figure as <7.5dB (I'm guessing its NF is
> not around 1dB) and the measured noise floor -175dBc/Hz at 10kHz and up at
> 400MHz from the datasheet.
> 
> Since I've had a need for a low-gain (2-4dB) isolation amp at the
> 100-500MHz range, I've experimented with a cascode design with Infineon's
> BFR106. Measured PN: -151dBc@100Hz, -161dBc@1k, -171dBc@10k and -178dBc at
> 100k and up (@400MHz). P1db should be around +15dBm and the NF was not
> measured yet.
> 
> Cheers,
> Leon
> 
> 
> >
> > -- Forwarded message --
> > From: John Miles 
> > To: "'Discussion of precise time and frequency measurement'" <
> > time-nuts@lists.febo.com>
> > Cc:
> > Bcc:
> > Date: Thu, 9 Jan 2020 22:23:23 -0800
> > Subject: Re: [time-nuts] low phase noise, noise floor and noise figure
> > amplifier at 400MHz
> > > Any suggestions on topologies, transistors, white papers, etc?  I'm
> > > considering the NXP BFU590Q silicon bipolar transistor, which I have used
> > in
> > > a transformer feedback configuration at 100MHz with less than -180dBc/Hz
> > > PN.
> >
> > You could take a look at the approach behind the option-K22 amplifiers that
> > were sold by HP for use with the 3048A.  I've got one of those but I needed
> > a couple more of them at one point, so I built some (literally) quick and
> > dirty copies with BFG591 transistors with good results.
> >
> > I've mentioned them before on here, I think.  There are a few photos and
> > plots at http://www.ke5fx.com/k22.htm .  Basically a CE amplifier with an
> > LED-referenced bias stage originally suggested by Bruce Griffiths.
> >
> > A single stage won't deliver the gain you're after, but these amplifiers
> > are
> > relatively well-behaved and can be cascaded at will.  That was the original
> > intent with the K22, which consisted of two independent amps in one box.
> > If
> > you want to use the K22 amps to keep oscillators from injection locking,
> > you
> > pretty much have to cascade them due to lack of reverse isolation.  The
> > homebrew hack job is similar to the HP original in most respects including
> > that one.
> >
> > I'd be inclined to use a dual-emitter part (BUF590G) instead of the
> > BUF590Q,
> > if I were building more of these.
> >
> > -- john, KE5FX
> >
> >
> >
> >
> >
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Re: [time-nuts] Norton amplifiers

[Bruce Griffiths]

Simulation indicates that the required C value depends on the transformer turns 
ratios and the RC product sets the notch frequency. 

Large signal modulation of the transistor parameters results in a distorted 
signal at the base when a large signal is applied to the output.

the RC product is around 4ns for a simulated 2N3904 for a reverse isolation 
notch at 10MHz. The value if C is a multiple (dependent on transformer turns 
ratio) of Ccb.

Bruce

> On 14 January 2020 at 09:01 Claudio Girardi via time-nuts 
> mailto:time-nuts@lists.febo.com > wrote:
> 
> 
> Some years ago I played a little with that buffer circuit and found out 
> that the isolation up to a few MHz can be improved a little with an RC 
> feedback network between base and collector.
> I cannot find my notes right now, IIRC from the output the circuit can be 
> seen as a sort of bridge where one can balance the various impedances for 
> minimum feedback.
> Enclosed is a graph for the measured gain and isolation for that circuit, 
> using a 2N3904 (!), for several configurations -
> without the RC feedback, with an RC combination giving some overall 
> improvement in S12 and with some values that gave a sharp null at 10 MHz.
> 
> Claudio
> 
> > > Il 13 gennaio 2020 alle 18.27 Jeffrey Pawlan  mailto:paw...@runbox.com > ha scritto:
> > 
> > 
> > Many years ago I did a study of Norton amplifiers and optimized for 
> > IP3
> > using non-linear circuit simulation tools. I published a two part
> > article in RF Design Magazine which covered the amplifier itself as 
> > well
> > as the non-linear model for the BJT. My use for the Norton 
> > amplifier did
> > not require high isolation so I spent little tile on that aspect. I 
> > am
> > friends with the co-inventor of the original and the author of the
> > subsequent patents. His name is Allen Podell.  The webpage you 
> > included
> > speculated that the reverse isolation degradation at high 
> > frequencies
> > was owing to the layout or the transformer. Although those are
> > contributors, the simulation showed high frequencies had poorer s12 
> > so
> > it is expected.
> > 
> > If high isolation is what you need, then as written on this list, 
> > there
> > are ICs which can provide this much better than a single stage
> > amplifier. They do suffer from more residual noise however.
> > 
> > Jeffrey Pawlan
> > 
> > 
> > ___
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Re: [time-nuts] 1 pps Accuracy in two locations

[Bruce Griffiths]

Except for some low tempco single mode fibers the delay tempco is on the order 
of 10ppm/K:
https://library.nrao.edu/public/memos/edtn/EDTN_168.pdf

Bruce 
> On 16 January 2020 at 23:29 Magnus Danielson  wrote:
> 
> 
> Hi,
> 
> On 2020-01-15 23:34, Attila Kinali wrote:
> > On Wed, 4 Dec 2019 09:40:34 -
> >  wrote:
> >
> >> I'm always being asked to provide equipment that can produce two 1 pps
> >> outputs aligned to each other to within a few ps.
> >>
> >> These two 1 pps pulses are not in the same location and could be 100 metres
> >> to a few km away.
> > As others have written, getting down to a few ps is not feasible, at least
> > not with the amount of money your customers are likely willing to pay.
> > To get down to these levels you will need to pull fibres from one location
> > to another and using special circuitry to activly compensate variation
> > in length due to temperature changes and vibration, even for burried fibres.
> > Just to put into perspective what your customers are asking for: in 1ps
> > light travels 300µm in vacuum/air or ~150µm in fibre/coax.
> 
> Let me correct that a little.
> 
> For fibre the relative dielectrics of the silica glass is just about
> 2.25 giving the index just about 1.5, which then gives the 300 um / 1.5
> to about 200 um. I am known to indicate the length of 1 ns in fibre
> betwen my index finger and thumb, roughly 2 dm, giving the delay for 1 m
> to be about 5 ns, letting the round-trip-time for 1 m be 10 ns which is
> a very handy number for rule of thumb conversions for fibre. If you look
> in more detail, the actual property depend on the wavelength being used
> and the temperature of the fibre, as this changes the actual delay.
> While first degree compensation is trivial in two-way systems, you end
> up having calibration issues.
> 
> Coax is less easy. If you have the normal RG58 crap, it aligns to about
> the same numbers as fiber, as the dielectrics is about the same.
> However, for more phase-stable cables with lower dielectric loss one
> simply has less dielectrics to start with, such as foam or other form of
> support for center conductor. That gives the relative dielectric go
> towards 1 and thus the velocity factor with that. It's much more a "it
> depends".
> 
> Other than that, I agree with the general analysis of Attila, it is
> close to my experience, and I've been working on these things
> commercially for over 10 years now. If you want to know how things works
> (or rather not work) in a telecom, it is even more painful than this.
> 
> So end conclusion being, if you required precision of 1 ps from a timing
> system, you are likely going to have one very expensive system and it
> will be a pain to operate, it may be worth considering if you are doing
> it the right way. I've seen requirements in the 10s of ps for a fixed
> system setup, but that is while challenging kind of doable, but then
> that requires quite a bit of additional control loops and knowing what
> one does.
> 
> Cheers,
> Magnus
> 
> 
> 
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Re: [time-nuts] 1 pps Accuracy in two locations

[Bruce Griffiths]

PSOF fiber has a much lower tempco:
https://accelconf.web.cern.ch/accelconf/p01/PAPERS/MPPH011.PDF

Bruce
> On 17 January 2020 at 00:08 Bruce Griffiths  
> wrote:
> 
> 
> Except for some low tempco single mode fibers the delay tempco is on the 
> order of 10ppm/K:
> https://library.nrao.edu/public/memos/edtn/EDTN_168.pdf
> 
> Bruce 
> > On 16 January 2020 at 23:29 Magnus Danielson  wrote:
> > 
> > 
> > Hi,
> > 
> > On 2020-01-15 23:34, Attila Kinali wrote:
> > > On Wed, 4 Dec 2019 09:40:34 -
> > >  wrote:
> > >
> > >> I'm always being asked to provide equipment that can produce two 1 pps
> > >> outputs aligned to each other to within a few ps.
> > >>
> > >> These two 1 pps pulses are not in the same location and could be 100 
> > >> metres
> > >> to a few km away.
> > > As others have written, getting down to a few ps is not feasible, at least
> > > not with the amount of money your customers are likely willing to pay.
> > > To get down to these levels you will need to pull fibres from one location
> > > to another and using special circuitry to activly compensate variation
> > > in length due to temperature changes and vibration, even for burried 
> > > fibres.
> > > Just to put into perspective what your customers are asking for: in 1ps
> > > light travels 300µm in vacuum/air or ~150µm in fibre/coax.
> > 
> > Let me correct that a little.
> > 
> > For fibre the relative dielectrics of the silica glass is just about
> > 2.25 giving the index just about 1.5, which then gives the 300 um / 1.5
> > to about 200 um. I am known to indicate the length of 1 ns in fibre
> > betwen my index finger and thumb, roughly 2 dm, giving the delay for 1 m
> > to be about 5 ns, letting the round-trip-time for 1 m be 10 ns which is
> > a very handy number for rule of thumb conversions for fibre. If you look
> > in more detail, the actual property depend on the wavelength being used
> > and the temperature of the fibre, as this changes the actual delay.
> > While first degree compensation is trivial in two-way systems, you end
> > up having calibration issues.
> > 
> > Coax is less easy. If you have the normal RG58 crap, it aligns to about
> > the same numbers as fiber, as the dielectrics is about the same.
> > However, for more phase-stable cables with lower dielectric loss one
> > simply has less dielectrics to start with, such as foam or other form of
> > support for center conductor. That gives the relative dielectric go
> > towards 1 and thus the velocity factor with that. It's much more a "it
> > depends".
> > 
> > Other than that, I agree with the general analysis of Attila, it is
> > close to my experience, and I've been working on these things
> > commercially for over 10 years now. If you want to know how things works
> > (or rather not work) in a telecom, it is even more painful than this.
> > 
> > So end conclusion being, if you required precision of 1 ps from a timing
> > system, you are likely going to have one very expensive system and it
> > will be a pain to operate, it may be worth considering if you are doing
> > it the right way. I've seen requirements in the 10s of ps for a fixed
> > system setup, but that is while challenging kind of doable, but then
> > that requires quite a bit of additional control loops and knowing what
> > one does.
> > 
> > Cheers,
> > Magnus
> > 
> > 
> > 
> > ___
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> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> 
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Re: [time-nuts] Pressure sensitivity of Rb vapor cell standards

[Bruce Griffiths]

Magnus

You need a linear polariser plus a quarter waveplate to produce circularly 
polarised light from unpolarised light. A quarter waveplate alone wont suffice. 
So called circular polarisers used with modern digital cameras comprise a 
polariser with the linear polariser oriented correctly with respect to the 
following quarter waveplate to produce circularly polarised light. No idea how 
effective these are at 780nm as quarter waveplates can be relatively narrowband 
unless an achromatic stack is used.
Does it matter whether LH or RH circularly polarised light is used?

Bruce 
> On 19 February 2020 at 01:42 Magnus Danielson  wrote:
> 
> 
> Hi,
> 
> On 2020-02-18 11:06, Attila Kinali wrote:
> > On Mon, 17 Feb 2020 18:16:04 -0600
> > magnus  wrote:
> >
> >> Hi,In the 5065 and most others, the light intensity is not stabilized.
> >> It should not be too hard to regulate the Rb lamp amplitude and servo
> >> it to light intensity from the detector. Didn't Poul-Henning check this?
> >
> > I still think, replacing the 5065 lamp with a 780nm LED would be worthwhile
> > to try. Yes, the LEDs have a broader spectrum than a lamp, but it is a lot
> > easier to keep it stable than a fluerescent lamp. It would also allow to
> > lower the temperature of the Rb cell to get to the zero tempco point (which
> > seems to be around 60°C for most mixtures).
> 
> Well, as I recall it one has to have a quarter-wave window to remove
> polarization issues, as that too creates light-shift issues. Also, one
> wants a beam-expander to optically cover more of the cavity than the
> direct laser do. I have a bunch of 780 nm LED-lasers for this purpose,
> but it would be fun to try even as quick-hack.
> 
> So, nothing unsolveable, but things to attend to.
> 
> Cheers,
> Magnus
> 
> 
> 
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Re: [time-nuts] Pressure sensitivity of Rb vapor cell standards

[Bruce Griffiths]

The wavelength of a laser diode can be tuned by varying its temperature and/or 
bias current.
Mode hopping during tuning can be an issue with standard FP laser diodes.
Single transverse and longitudinal mode operation is also desirable.
The laser wavelength has to be within a few picometers of the absorption line 
center before it can be served to the absorption line center. Typically 
longitudinal modes have a separation of a few tenths of a nanometer for FP 
laser diodes. AR coated laser diode chips with an external cavity are easier to 
tune without mode hopping.
A cateye resonator with a tilt tuned narrowband filter is easier to align than 
a Littrow or a Littman-Metcalf resonator.

VCSELs and DFB (with integral Bragg grating) can be better behaved but 
stabilising the polarisation mode is desirable for a VCSEL otherwise 
polarisation mode hopping can occur.

Bruce
> On 20 February 2020 at 10:29 Hal Murray  wrote:
> 
> 
> 
> > You will not be able to find one with the correct wavelength. An 
> > unstabilized
> > laser diode has an output bandwidth in the 50-300MHz range. Which means you
> > need to hit the right wavelength with the accuracy of the bandwidth of the
> > laser. For a bandwidth of 100MHz at 780nm that means you have to hit the
> > right wavelength with an accuracy of 0.2pm. The slightes vibration, the
> > slightest change in temperature, the slighest change of current through the
> > laser diode or a fly coughing and you are off. That's why you have to
> > actively steer the laser diode such that its output wavelength stays where
> > you want it to be. If you are using a laser, there is no way around it. 
> 
> What parameter do I adjust if I want to steer a laser?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] Are there SC-crystals out there in the wild that are not Overtone?

[Bruce Griffiths]

That's not relevant.
The idea is to see what frequency the crystal oscillates at not to build a high 
stability oscillator.
If can be made to oscillate at a frequency somewhere around 5MHz/3 then its 
likely a third overtone crystal.

Bruce
> On 28 February 2020 at 23:34 Attila Kinali  wrote:
> 
> 
> On Thu, 27 Feb 2020 08:45:16 -0800
> "Richard (Rick) Karlquist"  wrote:
> 
> > OTOH, you could build a simple Colpitts
> > oscillator and see where it oscillates.
> > That's what they did back in the dark
> > ages.
> > 
> > Any time nut should be up for that.
> 
> Yes, but how many of us can build a time-nuts quality oscillator?
> I'm still lacking that paper/book that teaches me how to build
> a high stability oscillator.
> 
> I have a couple of 5MHz 3rd OT SC cut crystals in HC-37 case sitting
> in a box, waiting to be used as some oscillator, I just lack the knowledge
> to make good use of them.
> 
>   Attila Kinali
> 
> -- 
> In science if you know what you are doing you should not be doing it.
> In engineering if you do not know what you are doing you should not be doing 
> it.
> -- Richard W. Hamming, The Art of Doing Science and Engineering
> 
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Re: [time-nuts] What is the BEST crystal?

[Bruce Griffiths]

IIRC Tolansky obtained some interferograms illustrating the surface deflections 
of these acoustic resonators.
I'll unearth my copy of Tolansky's book on optical interferometry and check.

Bruce
> On 01 March 2020 at 13:41 "John Moran, Scawby Design" 
>  wrote:
> 
> 
> Wow, that provoked an interesting discussion!
> 
> Thanks for all the information and references to further information - it 
> should keep me quiet for a while.
> 
> Interestingly 50mm diameter was about the diameter of the crystals used by 
> the British Post Office in the early days for generating a master oscillator. 
> It wasn't ground into a plano-convex lens but as a ring and was about 10mm 
> thick. Like the old WW2 crystals the electrodes weren't plated but just 
> contact rings. I have no idea what frequency they were ... by the time that I 
> realised they were scrapping all this kit it was gone and I only managed to 
> salvage two GPO Type 36 master 1S pendulums from a dumpster!
> 
> Thanks again for all the feedback.
> 
> John
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Re: [time-nuts] What is the BEST crystal?

[Bruce Griffiths]

Interferogram showing vibration nodes etc for quartz ring resonator frequency 
standard attached.

Bruce
> On 01 March 2020 at 14:27 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> It’s also the size of the 2.5 MHz 5th’s and similar parts made “way back”. 
> They went into glass packages 
> the size of door knobs. Packaging / design / mounting / processing has 
> changed a lot since then. 
> 
> Bob
> 
> > On Feb 29, 2020, at 7:41 PM, John Moran, Scawby Design 
> >  wrote:
> > 
> > Wow, that provoked an interesting discussion!
> > 
> > Thanks for all the information and references to further information - it 
> > should keep me quiet for a while.
> > 
> > Interestingly 50mm diameter was about the diameter of the crystals used by 
> > the British Post Office in the early days for generating a master 
> > oscillator. It wasn't ground into a plano-convex lens but as a ring and was 
> > about 10mm thick. Like the old WW2 crystals the electrodes weren't plated 
> > but just contact rings. I have no idea what frequency they were ... by the 
> > time that I realised they were scrapping all this kit it was gone and I 
> > only managed to salvage two GPO Type 36 master 1S pendulums from a dumpster!
> > 
> > Thanks again for all the feedback.
> > 
> > John
> > ___
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> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> 
> 
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Re: [time-nuts] What is the BEST crystal?

[Bruce Griffiths]

Dana

The text merely indicates that Tolansky and Bardsley obtained these images in 
1948.
The annular crystal was one of the NPL frequency standards of the time.

However, given that the fringes are multiple beam fringes, a high reflectivity 
electrode must lie on the top surface of the ring. 

There are also a stroboscopic interferogram of an oscillating quartz plate, 
probably at a frequency below a few hundred kHz given that RF modulation of the 
mercury vapour source is ineffective above a few hundred kHz or so.

Bruce
> On 02 March 2020 at 05:01 Dana Whitlow  wrote:
> 
> 
> Bruce, is there any text about the ring resonator which discusses the
> features in the
> interferogram?  Also I'd be interested in the configuration of the
> electrodes.
> 
> My present interpretation is that the vibratory resonance stems from
> contra-rotating
> modes each propagating around the ring, and that the fringe pattern is
> complicated
> by the two surfaces being a little bit out of parallel and with a hint of
> roughly spherical
> curvature relative to each other (probably not deliberate).
> 
> I used to do a good bit of holographic interferometry, mostly related to
> identifying
> resonances and vibratory modes of blades on jet turbine rotors, and it's
> hard to
> break the habit of trying to interpret interference patters.
> 
> Dana
> 
> 
> On Sat, Feb 29, 2020 at 7:34 PM Bruce Griffiths 
> wrote:
> 
> > Interferogram showing vibration nodes etc for quartz ring resonator
> > frequency standard attached.
> >
> > Bruce
> > > On 01 March 2020 at 14:27 Bob kb8tq  wrote:
> > >
> > >
> > > Hi
> > >
> > > It’s also the size of the 2.5 MHz 5th’s and similar parts made “way
> > back”. They went into glass packages
> > > the size of door knobs. Packaging / design / mounting / processing has
> > changed a lot since then.
> > >
> > > Bob
> > >
> > > > On Feb 29, 2020, at 7:41 PM, John Moran, Scawby Design <
> > j...@scawbydesign.co.uk> wrote:
> > > >
> > > > Wow, that provoked an interesting discussion!
> > > >
> > > > Thanks for all the information and references to further information -
> > it should keep me quiet for a while.
> > > >
> > > > Interestingly 50mm diameter was about the diameter of the crystals
> > used by the British Post Office in the early days for generating a master
> > oscillator. It wasn't ground into a plano-convex lens but as a ring and was
> > about 10mm thick. Like the old WW2 crystals the electrodes weren't plated
> > but just contact rings. I have no idea what frequency they were ... by the
> > time that I realised they were scrapping all this kit it was gone and I
> > only managed to salvage two GPO Type 36 master 1S pendulums from a dumpster!
> > > >
> > > > Thanks again for all the feedback.
> > > >
> > > > John
> > > > ___
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> > > > To unsubscribe, go to
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > > > and follow the instructions there.
> > >
> > >
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Re: [time-nuts] Noise Floor

[Bruce Griffiths]

The PN floor is somewhat lower with a 15dBm rather than a 4dBm input

http://www.ko4bb.com/getsimple/index.php?id=phase-noise-and-other-measurements-with-a-timepod

Bruce

> On 27 March 2020 at 06:11 kb...@n1k.org mailto:kb...@n1k.org wrote:
> 
> 
> Hi
> 
> Ok so here's a "new" part as opposed to one that is many decades old. 
> Again
> this is a part that has been talked about
> more than once on the list. The demo board is an early one, but I assume 
> it
> is representative of how the CMOS output
> part you get today works.
> 
> There are two runs. The first pretty clearly shows the part warming up. 
> The
> second still shows temperature effects,
> they just are not as obvious. If you *really* need to hit < 1x10^-15 at 
> 100
> seconds with this part, drafts are not a good thing.
> 
> The part is being driven with 4 dbm at 5 MHz. Max input is rated as 10 dbm
> so that's not as nutty as it sounds. 5 MHz ( or
> even 10 MHz) is well below the design target for this part. There's not a
> lot on the datasheet to compare to. As with the previous
> part, ADEV is pretty good (out to 100 sec). Phase noise is not in the 
> 10811
> class wideband. If you need low wideband phase noise
> as a logic signal at 5 MHz, you need to do something different. For ADEV,
> this will do just fine.
> 
> Bob
> 
> -Original Message-
> From: time-nuts  mailto:time-nuts-boun...@lists.febo.com > On Behalf Of Charles
> Steinmetz
> Sent: Wednesday, March 25, 2020 5:23 PM
> To: time-nuts@lists.febo.com mailto:time-nuts@lists.febo.com
> Subject: Re: [time-nuts] Noise Floor
> 
> Taka Kamiya wrote:
> 
> > > I've been playing around with Clifton amplifier as well. Mine, 
> input is
> > 
> > > terminated with 50 ohm register, and rest is unmodified, so it has 
> > 6dB gain.
> I have a 10dB pad on input side. I, too, noticed there will be a severe
> clipping with driving it too hard. * * * I with there was a little
> more room there
> 
> Bob wrote:
> >> Maybe there's some noise in those resistors
> >> Well. maybe not so much.
> >>
> >> If you drive this board so it has a couple db more output, it goes into
> clipping. When that happens  yuck.
> >> Noise and ADEV both are massively impacted.
> >> You very much do *not* want to overdrive this board. * * *
> >> I would stick with 12 dbm or less
> 
> You can buy some headroom by raising the supply voltage. There is an
> on-card LM78L09 9v voltage regulator (U902) that can safely be raised to
> 12v (LM78L12). This will get you cleanly to and a bit past the
> traditional +13 dBm (1v rms) standard reference level. Of course, you
> will need to make sure the raw supply voltage is >15v.
> 
> As to noise, the 200 ohm resistor on the opamp's noninverting input
> (R901) accounts for nearly 6dB of the amplifier noise (assuming an
> effective source impedance of 50 ohms). Reducing this to, say, 33 ohms
> will lower the noise floor a few dB.
> 
> Finally, the state of CFB video amplifier development has advanced
> dramatically in the 20 years since the AD8007 was introduced. New
> amplifiers with supply voltage ratings up to 36v are available (allowing
> about 10dB greater headroom than the 8007), and many of the newer opamps
> clip much more gracefully than the 8007 when you do hit the limit (but
> you really want not to do that in any measurement application).
> 
> Many of these new CFB amplifiers have been discussed here on the list,
> and each has its own fans. One I like that doesn't get mentioned much
> is the LME49713. It is discontinued, but still available from Rochester
> Electronics and others. But there are lots of good choices.
> 
> Best regards,
> 
> Charles
> 
> 
> 
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Re: [time-nuts] Crystal filters in test equipment

[Bruce Griffiths]

A constant temperature oven for the crystal filter may be required to minimise 
the crystal filter phase shift tempco contribution to the output phase 
stability. 

Bruce
> On 27 March 2020 at 11:03 Perry Sandeen via time-nuts 
>  wrote:
> 
> 
> Learned Gentlemen,
> Both the HP 106 and 107 have a post oscillator crystal filter.  There is also 
> a 10 MHz crystal filter used in my Tracor 527E FDM.
> So the question I have is there anything to be gained by adding 10 MHz 
> crystal filters to the 10811 and similar OCXO's?  They are very inexpensive 
> to purchase.
> Regards,
> Perrier
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Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

One can merely add diodes to the opamp feedback network form a feedback limiter 
and maintain the opamp outputs within the range for which the opamp is well 
behaved whilst maintaining the increase in slew rate for the output.

Bruce
> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> 
> 
> Jup, some of them even have phase reversal when they are overloaded, so it
> is perhaps not a good idea in general, but I think there are opamps which
> are specified for this.
> 
> Tobias
> 
> 
> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow  wrote:
> 
> > Caution: opamps make terrible limiters- their overload behavior is
> > generally ugly
> > and unpredictable.  It's much better to use a genuine level comparator, and
> > wire it
> > up so that it has a modest amount of hysteresis.
> >
> > Dana
> >
> >
> > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> >
> > > Hi
> > >
> > > The quick way to do this is with a single mixer. Take something like an
> > old
> > > 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
> > >
> > > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
> > > That tone is the *difference* between the 10811 and your device under
> > > test.
> > > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> > >
> > > If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> > > shift
> > > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
> > > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
> > >
> > > *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
> > > that
> > > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > > second.
> > >
> > > The reason its not quite that simple is that the input circuit on the
> > > counter
> > > really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
> > > RF signal. Instead of getting 9 digits a second, you probably will get
> > > three
> > > *good* digits a second and another 6 digits of noise.
> > >
> > > The good news is that an op amp used as a preamp ( to get you up to maybe
> > > 32 V p-p rather than a volt or so) and another op amp or three as
> > limiters
> > > will
> > > get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
> > > and low pass filter ( DC offsets can be a problem ….) and you have a
> > > working
> > > device that gets into the parts in 10^-13 with your 5335.
> > >
> > > It all can be done with point to point wiring. No need for a PCB layout.
> > > Be
> > > careful that the +/- 18V supplies to the op amp *both* go on and off at
> > > the
> > > same time ….
> > >
> > > Bob
> > >
> > > > On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
> > > >
> > > > hi John
> > > >
> > > > yes I know the DMTD method, and indeed I am planing to build my own
> > DMTD
> > > > system, something similar to the "Small DMTD system" published by
> > Riley (
> > > > https://www.wriley.com/A Small DMTD System.pdf).
> > > > However I am unsure whether that will help much in this case, because
> > all
> > > > what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal
> > or
> > > > so which can be measured more easily, and I already have 1Hz signals
> > (the
> > > > 1PPS) which I am comparing.
> > > > Or do you suggest to use the DMTD and use a higher frequency at its
> > > > outputs, say 10Hz or so, and then average for 10 samples  to increase
> > the
> > > > resolution?
> > > >
> > > > Thanks
> > > > Tobias
> > > > HB9FSX
> > > >
> > > >
> > > > On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
> > > >
> > > >>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
> > > >> does
> > > >>> my counter need? If the above was true, I would expect that a 1ps
> > > >>> resolution (and an even better stability!) was required to measure
> > ADEV
> > > >> of
> > > >>> 1e-12, The fact that the (as far as I know) world's most recent,
> > > >>> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> > > >>> resolution, but people are still able to measure even 1e-14 shows
> > that
> > > my
> > > >>> assumption is wrong. So how are the measurement resolution and the
> > ADEV
> > > >>> related to each other? I plan to build my own TIC based on a TDC7200,
> > > >> which
> > > >>> would offer some 55ps of resolution, but how low could I go with
> > that?
> > > >>
> > > >> That sounds like a simple question but it's not.  There are a few
> > > >> different approaches to look into:
> > > >>
> > > >> 1) Use averaging with your existing counter.  Some counters can yield
> > > >> readings in the 1E-12 region at t=1s even though their single-shot
> > > jitter
> > > >> is much worse than that.  They do this by averaging  hundreds or
> > > thousands
> > > >> of samples for each reading they report.  Whether (and when) this is
> > > >> acceptable is a complex topic in itself, too much so to explain
> > quickly.
> > > >> Search for information on the effects of averagin

Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

Tobias

That would certainly work for a start and have a better performance that a 
counter front end.
The performance can be estimated using the tools at the link Bob provided.
Lower noise opamps will improve the performance somewhat.
A wider bandwidth opamp with a higher slew rate may be useful for the final 
stage of a Collins style zero crossing  detector. 
The RPD series of phase detectors will have better performance than the TUF-1.
For the ultimate performance at low offset frequencies one can build a mixer 
using diode connected BJTs as NIST have done.

Bruce
> On 04 April 2020 at 12:38 Tobias Pluess  wrote:
> 
> 
> Hi Bruce
> 
> I have some TUF-1 mixers in my junk box as well as some JFET OpAmps AD8626.
> So, if I connect the OpAmps appropriately with some diode limiters as you
> suggest, would you say this would give an acceptable DMTD system?
> If so it sounds like something that can easily be built on a breadbord or
> in manhattan style, as Bob already mentioned. That would be really cool.
> I think a while ago I asked a question which goes in a similar direction -
> which mixers are better as phase detectors (to build a PLL for phase noise
> measurement) and which ones should be used as actual mixers (like in this
> case).
> 
> 
> Tobias
> HB9FSX
> 
> On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths, 
> wrote:
> 
> > One can merely add diodes to the opamp feedback network form a feedback
> > limiter and maintain the opamp outputs within the range for which the opamp
> > is well behaved whilst maintaining the increase in slew rate for the output.
> >
> > Bruce
> > > On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> > >
> > >
> > > Jup, some of them even have phase reversal when they are overloaded, so
> > it
> > > is perhaps not a good idea in general, but I think there are opamps which
> > > are specified for this.
> > >
> > > Tobias
> > >
> > >
> > > On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
> > wrote:
> > >
> > > > Caution: opamps make terrible limiters- their overload behavior is
> > > > generally ugly
> > > > and unpredictable.  It's much better to use a genuine level
> > comparator, and
> > > > wire it
> > > > up so that it has a modest amount of hysteresis.
> > > >
> > > > Dana
> > > >
> > > >
> > > > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> > > >
> > > > > Hi
> > > > >
> > > > > The quick way to do this is with a single mixer. Take something like
> > an
> > > > old
> > > > > 10811 and use the coarse tune to set it high in frequency by 5 to 10
> > Hz.
> > > > >
> > > > > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
> > tone.
> > > > > That tone is the *difference* between the 10811 and your device under
> > > > > test.
> > > > > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> > > > >
> > > > > If you measured the 10 MHz on the DUT, that 1 Hz would be a very
> > small
> > > > > shift
> > > > > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
> > change
> > > > > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
> > increase ).
> > > > >
> > > > > *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s
> > not
> > > > > that
> > > > > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > > > > second.
> > > > >
> > > > > The reason its not quite that simple is that the input circuit on the
> > > > > counter
> > > > > really does not handle a 10 Hz audio tone as well as it handles a 10
> > MHz
> > > > > RF signal. Instead of getting 9 digits a second, you probably will
> > get
> > > > > three
> > > > > *good* digits a second and another 6 digits of noise.
> > > > >
> > > > > The good news is that an op amp used as a preamp ( to get you up to
> > maybe
> > > > > 32 V p-p rather than a volt or so) and another op amp or three as
> > > > limiters
> > > > > will
> > > > > get you up around 6 or 7 good digits. Toss in a cap or two as a high
> > pass
> > > > > and low pass filter ( DC offsets can be a problem ….) and you have a
> > > > > working
> > > > > devi

Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

Tobias

The diode connected BJT (2N) mixer is compared with various commercial 
mixers and phase detectors in a NIST paper that has a graph showing the PN of 
various mixers as a function of offset frequency.

The RPD series phase detectors have a higher output and lower PN than most 
mixers.
The output depends on the input characteristics of the lowpass filter at the IF 
output.
A capacitive load at this port increases the output at the expense of isolation 
between ports etc.
These interactions are clearly shown in Spice simulations of such mixers.

Bruce 

> On 04 April 2020 at 13:09 Tobias Pluess  wrote:
> 
> 
> Hi Bruce
> 
> the NIST design you mentioned - do you mean that publication where they
> used 2N's for a diode ring mixer? if so I can perhaps build this as
> well because I think I even have some 2Ns in my home lab :-)
> Concerning the RPD vs. TUF mixers - what is the actual property which makes
> the RPD "better" than the TUF?
> 
> Thanks,
> Tobias
> 
> On Sat., 4 Apr. 2020, 02:01 Bruce Griffiths, 
> wrote:
> 
> > Tobias
> >
> > That would certainly work for a start and have a better performance that a
> > counter front end.
> > The performance can be estimated using the tools at the link Bob provided.
> > Lower noise opamps will improve the performance somewhat.
> > A wider bandwidth opamp with a higher slew rate may be useful for the
> > final stage of a Collins style zero crossing  detector.
> > The RPD series of phase detectors will have better performance than the
> > TUF-1.
> > For the ultimate performance at low offset frequencies one can build a
> > mixer using diode connected BJTs as NIST have done.
> >
> > Bruce
> > > On 04 April 2020 at 12:38 Tobias Pluess  wrote:
> > >
> > >
> > > Hi Bruce
> > >
> > > I have some TUF-1 mixers in my junk box as well as some JFET OpAmps
> > AD8626.
> > > So, if I connect the OpAmps appropriately with some diode limiters as you
> > > suggest, would you say this would give an acceptable DMTD system?
> > > If so it sounds like something that can easily be built on a breadbord or
> > > in manhattan style, as Bob already mentioned. That would be really cool.
> > > I think a while ago I asked a question which goes in a similar direction
> > -
> > > which mixers are better as phase detectors (to build a PLL for phase
> > noise
> > > measurement) and which ones should be used as actual mixers (like in this
> > > case).
> > >
> > >
> > > Tobias
> > > HB9FSX
> > >
> > > On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths,  > >
> > > wrote:
> > >
> > > > One can merely add diodes to the opamp feedback network form a feedback
> > > > limiter and maintain the opamp outputs within the range for which the
> > opamp
> > > > is well behaved whilst maintaining the increase in slew rate for the
> > output.
> > > >
> > > > Bruce
> > > > > On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> > > > >
> > > > >
> > > > > Jup, some of them even have phase reversal when they are overloaded,
> > so
> > > > it
> > > > > is perhaps not a good idea in general, but I think there are opamps
> > which
> > > > > are specified for this.
> > > > >
> > > > > Tobias
> > > > >
> > > > >
> > > > > On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
> > > > wrote:
> > > > >
> > > > > > Caution: opamps make terrible limiters- their overload behavior is
> > > > > > generally ugly
> > > > > > and unpredictable.  It's much better to use a genuine level
> > > > comparator, and
> > > > > > wire it
> > > > > > up so that it has a modest amount of hysteresis.
> > > > > >
> > > > > > Dana
> > > > > >
> > > > > >
> > > > > > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> > > > > >
> > > > > > > Hi
> > > > > > >
> > > > > > > The quick way to do this is with a single mixer. Take something
> > like
> > > > an
> > > > > > old
> > > > > > > 10811 and use the coarse tune to set it high in frequency by 5
> > to 10
> > > > Hz.
> > > > > > >
> > > > > > > Then feed it into

Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

An OP37 may  not function well as a diode clamped limiter since the loop gain 
is <5 during limiting.
A unity gain stable opamp would likely be better.

Bruce
> On 17 April 2020 at 09:26 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> The OP-37 is fine as long as the gain is over 5X. Under that gain level, you 
> need to run an OP-27. The OP-07 is pretty noisy. 
> 
> Limiter circuits have been covered in a lot of detail. One quick read is at:
> 
> http://www.ko4bb.com/getsimple/index.php?id=bruces-zero-crossing-detectors 
> 
> 
> That page and the others Bruce did go into a lot of detail on the how and 
> why of this kind of limiter. There are other resources out there as well. 
> 
> So yes, there are circuits that work better for this than others. 
> 
> Bob
> 
> > On Apr 16, 2020, at 3:46 PM, Tobias Pluess  wrote:
> > 
> > Hey Bob
> > 
> > awesome, I actually have found some OP-07 and OP-37 in my junkbox! going to
> > build an amplifier now for my mixers. Is it a wise idea to add diodes to
> > prevent the amplifier from clipping?
> > For example I would have done it similar to this
> > 
> > https://www.allaboutcircuits.com/technical-articles/an-op-amp-limiter-how-to-limit-the-amplitude-of-amplified-signals/
> > 
> > but I don't know whether this is a timenuts-grade circuit.
> > 
> > 
> > Tobias
> > 
> > 
> > On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
> > 
> >> Hi
> >> 
> >>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >>> 
> >>> Hi Bob
> >>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >>> 
> >>> Maybe I have some good OpAmps for this purpose in my box. I will try it!
> >> of
> >> 
> >> You need something that is quiet (like the OP-37) and has a pretty good
> >> slew
> >> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> >> one.
> >> 
> >>> course I saw that my setup was not ideal as there was a bit of noise on
> >> the
> >>> signals which I guess does lead to some jitter in the trigger circuit and
> >>> therefore decreases my measurement noise floor.
> >> 
> >> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> >> digits.
> >> Net result is a measurement that’s good in the vicinity of parts in 10^-13
> >> 
> >>> 
> >>> Can you say something about how it would be done using a TIC?
> >>> I don't have two identically good counters, but the HP 5335A could be
> >> used
> >>> as TIC, couldn't it.
> >> 
> >> The standard way of doing the test is to run two counters / two TIC/s /
> >> two whatever’s.
> >> I know of no practical way to do it with a single 5335.
> >> 
> >>> 
> >>> And the offset source I used is not directly the HP 10811, but the HP
> >> 8663A
> >>> Signal generator internally uses a 10811 as reference source. But I
> >> didn't
> >>> wait for days for it to warm up properly. (Should I?)
> >> 
> >> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
> >> you
> >> use the 10811, it needs to be on for a while. How long very much depends
> >> on
> >> just how long it’s been off. Best to keep it on all the time.
> >> 
> >>> 
>  Fun !!!
> >>> Yea, of course! :-)
> >>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> >>> myself. I use TimeLab to see what numbers I should expect, and then I
> >> want
> >>> to compute it all myself in Matlab because I want to see how it actually
> >>> works. ;-)
> >> 
> >> Be careful any time you code this stuff for the first time. It’s amazingly
> >> easy
> >> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
> >> you should not code it up yourself. I generally do it in Excel or in C.
> >> 
> >> Bob
> >> 
> >>> 
> >>> 
> >>> Best
> >>> Tobias
> >>> 
> >>> 
> >>> 
> >>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> >>> 
>  Hi
>  
>  Ok, first the math:
>  
>  If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>  
>  10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>  
>  You get to add a 6 to what Time Lab shows you.
>  
>  If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>  gets you to 1x10^-10
>  
>  So, what’s going on?
>  
>  You can’t feed the mixer outputs straight into a counter. The counter
>  front
>  end does not handle LF audio sine waves very well. You need to do an
>  op-amp based limiter. A pair of OP-37’s in each leg ( or something
>  similar)
>  should do the trick.
>  
>  Second, the offset source needs to be pretty good. A 10811 tuned high
> >> with
>  both the mechanical trim and the EFC is a pretty good choice to start
> >> out.
>  
>  If you only have one counter, simply ignore the second channel. You are
> >> now
>  running a single mixer. It still works as a comparison between the
> >> offset
>  oscillator
>  and your DUT.
>  
>  If you want to do it pr

Re: [time-nuts] f-multipliers from VHF to 10 GHz

[Bruce Griffiths]

Macom also do NLTL comb generators which are much quieter than SRDs:
https://www.macom.com/products/product-detail/MLPNC-7100-SMA850

Bruce
> On 16 May 2020 at 09:14 Gerhard Hoffmann  
> wrote:
> 
> 
> No, no, no, it's not that bad :-)  I should not post here in the middle 
> of the night. Sorry to cause that confusion.
> 
> Minimum  is -90 dBc @ 50 Hz, or let's say @100 Hz @ 10 GHz.
> that would equal -110 dBc@1 GHz,   or -130 dBc @100 MHz, BTDT.
> 
> And then, the ~4 MHz difference between TX and RX frequency could be
> done by a SSB mixer with a non-multiplied crystal. We would have some
> common mode noise, but the RX-TX difference would be fairly constant.
> It would not de-correlate over the 10 mm run length, not at low
> offsets where it counts.
> 
> The -110 was only meant for "Don't care about multiplied white noise
> floor", not in the sense of a spec but in the sense of "guaranteed
> harmless". It's not such a great relaxation after all, it could be
> 20 dB looser.
> 
> The question was really only about a _simple_ multiplier chain. The
> style used in ham radio 10 GHz transverters has too many stages,
> GaAS-Fets with 1/f and pipe cap filters. Too complicated.
> 
> Macom still make a SRD diode, but probably it is easiest to phaselock
> a ceramic puck or an on-chip VCO to a 100+ MHz crystal. The offset-
> mixing removes the need for a low reference frequency or fractional
> voodoo.
> 
> cheers, Gerhard
> 
> 
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Re: [time-nuts] f-multipliers from VHF to 10 GHz

[Bruce Griffiths]

Indicative price:
https://www.richardsonrfpd.com/Products/Product/MLPNC-7103-SMT6

Bruce
> On 16 May 2020 at 10:54 ed breya  wrote:
> 
> 
> Bruce wrote
> 
> Macom also do NLTL comb generators which are much quieter than SRDs:
> https://www.macom.com/products/product-detail/MLPNC-7100-SMA850
> 
> Wow, those are nice. I've studied and searched for NLTLs over the years, 
> and found all sorts of research papers about making monolithic ones, but 
> not such a finished piece that you can order up and go - even though 
> these may have been around for some time. I've even considered trying to 
> build some discretely and experiment, but got dissuaded when I found out 
> how many compression stages are needed for meaningful results. I think 
> that's why the research was all geared toward making them in integrated 
> form, where you can get lots of similar items repeated in tiny form. I'd 
> guess that these may have 20-100 stages, or maybe nowadays it can be one 
> continuous line with spatially variable characteristics..
> 
> It's cool to see, but probably quite spendy - I'd guess 2 grand or more. 
> I tried to find out the price looking at a distributor, but it's a 
> special order, call for quote type deal. I'm sure it's quite a few dB$ 
> above what I can justify for any of my projects.
> 
> Ed
> 
> 
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Re: [time-nuts] Trigger circuit for TIC

[Bruce Griffiths]

There is no universal circuit that minimises jitter for all signals without 
some tuning to suit the input frequency and threshold crossing slew rate. The 
LTC6957 works well for higher frequency sine waves. The low frequency sine wave 
outputs of a DMTD require a set of cascaded lowpass filtered limiters akin to 
those detailed on Oliver Collins classic paper on the design of zero crossing 
detectors before the LTC6957.  

Bruce
> On 03 June 2020 at 21:49 Tobias Pluess  wrote:
> 
> 
> Dear colleagues
> I am currently thinking about a concept for my own TIC. While I gathered
> some knowledge during my GPSDO project about using the TDC7200 as
> interpolator, I have not yet a good idea how I should design the input
> stage of a TIC. It should be somewhat universal, i.e. it should be usable
> with analog sine waves as well as with digital signals (TTL).
> 
> So the trigger input circuit shall accept a signal of less than approx. 5
> volts amplitude, and provide a digital output signal (3.3V logic level)
> which can then be used for further processing. It would be good if I could
> directly feed it with the output signals from a DMTD, but could also
> connect the 1PPS output signals of GPSDOs to it.
> I know that trigger jitter can be a problem, especially when the signals
> have small amplitudes and are sine instead of square. So what should I
> consider to minimise this effect?
> I have seen some schematics where people used ADCMP comparators, but I have
> forgotten which one exactly and I cannot remember where I saw it. On the
> other hand, on other pages I read that comparators are not recommended
> because they have a higher jitter, and it was recommended to use high-gain
> amplifiers instead.
> So what is the "proper" way to design such a trigger circuit which is
> usable for sine as well as square waves?
> (if the jitter was not critical, I would simply use some comparators.)
> 
> Background: I want to construct something like a timestamping counter which
> allows me to caracterise my GPSDO I built. For this, I would like to do
> different things: first, I want to compare the 1PPS signals of different
> GPSDOs with respect to mine (5V TTL signals), but on the other hand, I also
> want to use the DMTD method which provides signals with maybe some 10Hz
> frequency and several 100mV amplitude. It would be good if there was a
> trigger circuit which could be used for both.
> 
> 
> 
> BR
> Tobias
> HB9FSX
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Re: [time-nuts] Coherent optical clock down-conversion for microwave frequencies with 10^−18 instability

[Bruce Griffiths]

https://tf.nist.gov/general/pdf/3093.pdf
is likely more accessible than the sciencemag link

Bruce
> On 05 June 2020 at 11:15 Bill Byrom  wrote:
> 
> 
> This was published in the 22 May 2020 issue of Science (AAAS journal). For 
> AAAS members, the direct link is:
> https://science.sciencemag.org/content/368/6493/889 
> 
> They make use of a fiber-based OFC (optical frequency comb) and 
> state-of-the-art photodetectors to transfer optical clock stability to a 10 
> GHz microwave signal. This downconversion from optical to microwave was done 
> with an error of no more than 10-19 (1 x 10 ^-19). The best available optical 
> clock stability is around 10-18 (1 x 10^-18) at a couple of hundred seconds 
> averaging time. 
> 
> This specific experiment compared two independent Yb (Ytterbium) optical 
> lattice clocks running at about 259 THz. One Yb clock drove a 208 MHz comb 
> generator, while the other Yb clock drove a 156 MHz comb generator. Then:
> 208 MHz x 48th harmonic = 9.984 GHz
> 156 MHz x 64th harmonic = 9.984 GHz
> The phase between these 9.984 GHz signals was compared in a mixer phase 
> detector. The fractional frequency instability observed was 10-16 (1 x 
> 10^-16) over a 1 second interval. The frequencies I listed above are 
> approximate -- they actually measured a 1.5 MHz beat note between the ~10 GHz 
> signals. This allowed them to achieve a relative timing error of 900 
> attoseconds (rms).
> 
> The optical phase measurements between the two Yb clocks at 259 THz indicated 
> a frequency offset (Yb1 - Yb2) of 0.064 Hz, and the microwave ~10 GHz 
> comparison was consistent with that offset (2.5 +/- 0.6) x 10-20 (10^-20).
> 
> The abstract is:
> > Optical atomic clocks are poised to redefine the Système International (SI) 
> > second, thanks to stability
> > and accuracy more than 100 times better than the current microwave atomic 
> > clock standard. However,
> > the best optical clocks have not seen their performance transferred to the 
> > electronic domain, where
> > radar, navigation, communications, and fundamental research rely on less 
> > stable microwave sources.
> > By comparing two independent optical-to-electronic signal generators, we 
> > demonstrate a 10-gigahertz
> > microwave signal with phase that exactly tracks that of the optical clock 
> > phase from which it is derived,
> > yielding an absolute fractional frequency instability of 1 × 10−18 in the 
> > electronic domain. Such faithful
> > reproduction of the optical clock phase expands the opportunities for 
> > optical clocks both technologically
> > and scientifically for time dissemination, navigation, and long-baseline 
> > interferometric imaging.
> 
> I have a Science subscription and can read this paper, but I can't distribute 
> it here. 
> 
> You can also see discussion of this achievement by NIST (with assistance by 
> the University of Virginia) at Physics World:
> https://physicsworld.com/a/microwave-timing-signals-get-hundredfold-boost-in-stability/
>  
> You may need to request a free account at Physics World to read this article. 
> 
> --
> Bill Byrom N5BB
> 
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Re: [time-nuts] Coherent optical clock down-conversion for microwave frequencies with 10^−18 instability

[Bruce Griffiths]

https://tf.nist.gov/general/pdf/2995.pdf
may be also of some interest.
Its about optimising the linearity of high speed photodiodes.
These are used (amongst other applications )as mixers for converting optical 
combs to microwave signals.

Bruce 
> On 05 June 2020 at 11:35 Bill Byrom  wrote:
> 
> 
> Thanks, Bruce! That's a copy of that same Science article. I guess that NIST 
> got permission to post it on their website, since they were the sponsor of 
> the study. 
> --
> Bill N5BB
> 
> 
> On Thu, Jun 4, 2020, at 6:32 PM, Bruce Griffiths wrote:
> > https://tf.nist.gov/general/pdf/3093.pdf
> > is likely more accessible than the sciencemag link
> > 
> > Bruce
> > > On 05 June 2020 at 11:15 Bill Byrom  wrote:
> > > 
> > > 
> > > This was published in the 22 May 2020 issue of Science (AAAS journal). 
> > > For AAAS members, the direct link is:
> > > https://science.sciencemag.org/content/368/6493/889 
> > > 
> > > They make use of a fiber-based OFC (optical frequency comb) and 
> > > state-of-the-art photodetectors to transfer optical clock stability to a 
> > > 10 GHz microwave signal. This downconversion from optical to microwave 
> > > was done with an error of no more than 10-19 (1 x 10 ^-19). The best 
> > > available optical clock stability is around 10-18 (1 x 10^-18) at a 
> > > couple of hundred seconds averaging time. 
> > > 
> > > This specific experiment compared two independent Yb (Ytterbium) optical 
> > > lattice clocks running at about 259 THz. One Yb clock drove a 208 MHz 
> > > comb generator, while the other Yb clock drove a 156 MHz comb generator. 
> > > Then:
> > > 208 MHz x 48th harmonic = 9.984 GHz
> > > 156 MHz x 64th harmonic = 9.984 GHz
> > > The phase between these 9.984 GHz signals was compared in a mixer phase 
> > > detector. The fractional frequency instability observed was 10-16 (1 x 
> > > 10^-16) over a 1 second interval. The frequencies I listed above are 
> > > approximate -- they actually measured a 1.5 MHz beat note between the ~10 
> > > GHz signals. This allowed them to achieve a relative timing error of 900 
> > > attoseconds (rms).
> > > 
> > > The optical phase measurements between the two Yb clocks at 259 THz 
> > > indicated a frequency offset (Yb1 - Yb2) of 0.064 Hz, and the 
> > > microwave ~10 GHz comparison was consistent with that offset (2.5 +/- 
> > > 0.6) x 10-20 (10^-20).
> > > 
> > > The abstract is:
> > > > Optical atomic clocks are poised to redefine the Système International 
> > > > (SI) second, thanks to stability
> > > > and accuracy more than 100 times better than the current microwave 
> > > > atomic clock standard. However,
> > > > the best optical clocks have not seen their performance transferred to 
> > > > the electronic domain, where
> > > > radar, navigation, communications, and fundamental research rely on 
> > > > less stable microwave sources.
> > > > By comparing two independent optical-to-electronic signal generators, 
> > > > we demonstrate a 10-gigahertz
> > > > microwave signal with phase that exactly tracks that of the optical 
> > > > clock phase from which it is derived,
> > > > yielding an absolute fractional frequency instability of 1 × 10−18 in 
> > > > the electronic domain. Such faithful
> > > > reproduction of the optical clock phase expands the opportunities for 
> > > > optical clocks both technologically
> > > > and scientifically for time dissemination, navigation, and 
> > > > long-baseline interferometric imaging.
> > > 
> > > I have a Science subscription and can read this paper, but I can't 
> > > distribute it here. 
> > > 
> > > You can also see discussion of this achievement by NIST (with assistance 
> > > by the University of Virginia) at Physics World:
> > > https://physicsworld.com/a/microwave-timing-signals-get-hundredfold-boost-in-stability/
> > >  
> > > You may need to request a free account at Physics World to read this 
> > > article. 
> > > 
> > > --
> > > Bill Byrom N5BB
> > > 
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Re: [time-nuts] low power divide by 5

[Bruce Griffiths]

For fixed frequency operation there's always Wenzel's divider using a D FF with 
LC feedback:
http://www.wenzel.com/wp-content/uploads/dividers.pdf
At least the power consumption is low.

Bruce
> On 03 July 2020 at 12:35 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> > On Jul 2, 2020, at 6:38 PM, jimlux  wrote:
> > 
> > On 7/2/20 2:50 PM, Bob kb8tq wrote:
> >> Hi
> >>> On Jul 2, 2020, at 5:30 PM, jimlux  wrote:
> >>> 
> >>> On 7/2/20 11:37 AM, ed breya wrote:
>  It's been fun reminiscing about all these dividers and techniques, but 
>  getting back to the OP, the original search was for a divide by 5 with 
>  "low power" and operation from 5 to possibly 3.3V, and clocking properly 
>  at 50 MHz. One would assume also minimal size and complexity, and low 
>  cost.
> >>> 
> >>> You forgot to add rad-hard.. I was the OP - This has been a fascinating 
> >>> thing - we have a breadboard that uses a fancy clock distribution chip 
> >>> that consumes close to a watt (and has too much jitter, as well)..
> >> 
> >>> 3) It's hard to even find programmable logic that is simple and small. 
> >>> All the mfrs tout their latest tiny parts with *only half a million 
> >>> gates* (I exaggerate, but you get the picture)
> >> If they want to sell you a fully self contained "million gate" device for 
> >> a couple bucks, is that really
> >> a bad thing?  Sure, if it’s in a thousand pin BGA, it’s a bad thing. If 
> >> it’s in a < 40 pin package that
> >> you can get on a small board …. maybe not so much.
> > 
> > yes, if it's in a small pinout package. One other peculiarity that I've 
> > been burned by is that a lot of the modern devices with large logic and few 
> > I/O pins have power dissipations that are clock rate independent for the 
> > internal logic - it's the leakage current that dominates and that's VERY 
> > dependent on die temp.
> > 
> > 
> > I think though, that the marketplace is driving towards increased 
> > functionality on one chip, with bigger die size. Those of us who want 50 
> > gates at medium or low speed are distinctly in the minority.
> 
> There are very few applications that require that sort of device. Volume
> matters ( a lot !!)
> 
> Bob
> 
> 
> > 
> > 
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Re: [time-nuts] low power divide by 5

[Bruce Griffiths]

When simulating the Wenzel divider its important to include the input 
protection diodes or the input signal at the D input of the FF becomes 
unrealistically large even with a finite Q inductor.

Bruce
> On 03 July 2020 at 20:18 glenlist  wrote:
> 
> 
> Bravo Microchip for extending the ECL lines.
> 
> I use quite a few of them like  SY100EL33L (div 4 ).  I needed a 400 MHz 
>  >> 100 MHz divider for driving the CPU clock from the ADC clock.  ECL. 
> yeah overkill.
> 
> (74)AC doesnt quite make it. Wow- newish 74AUC will go to 300 MHz at 
> 1.8V. ..
> 
> Anyway the SY100EL33L  is cheap. and 3.3V. ..even if the package is 
> giant. (SOIC8) .
> 
> But I like the Wenzel  skip divider- now that is cool- Thanks BRUCE for 
> posting that.  (http://www.wenzel.com/wp-content/uploads/dividers.pdf)
> 
> 
> glen
> 
> 
> On 03/07/2020 11:54, ed breya wrote:
> > Jim,
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Re: [time-nuts] IFCS 2020 tutorial - low noise electronics for time/frequency metrology

[Bruce Griffiths]

Attila

Another example somewhat similar to the DMTD is the Receiver in a laser DMI 
(Distance Measuring Interferometer). A photomixer the typical implementation 
consists of a photomixer (eg photodiode connected between gate and drain of 
NJFET source follower with boostrapped drain) + linear preamp + manually 
adjustable gain differential amplifier (eg MC1590) + differential line receiver.
The performance of this signal chain could likely be improved somewhat.
The distance moved is equal to the integral of the change in beat frequency 
between a pair of orthogonally polarised laser modes. A reference channel with 
stationary parts provides the frequency difference signal between the 2 modes 
as produced by the laser. The beat frequency is typically a few MHz (eg ~ 
2MHz). Input signal levels at the photomixer are typically a few tens of 
microwatts (eg 50 uW) or so.

The small signal gain of the BJT differential pair you show is actually 
2R/[2*(kT/(e*(I/2)))]  =IR/(2kT/e).

Bruce
> On 08 July 2020 at 14:25 Attila Kinali  wrote:
> 
> 
> Moin,
> 
> As some of you know, I have been allowed to give a tutorial on low noise 
> electronics
> for this year's IFCS. As the whole conference has been turned into a virtual 
> one,
> we were asked to record our tutorials and upload them. Additonally to the 
> conference
> I decided to put my tutorial online for everyone to watch. You can find it at
> http://time.kinali.ch/ifcs_2020_tutorial/
> Though, I have to honestly admit, I am not proud of it. There is too much that
> I couldn't fit what should be in there, in in the 75' we were given. And 
> there is
> quite a few things that I think I made too confusing. Nevertheless I hope it 
> can
> be of use for some. Please let me know what you think, especially if you have 
> ideas
> how I could improve the tutorial for the next time I'm giving it.
> 
> 
>   Attila Kinali
> 
> PS: As this years IFCS is fully virtual, the registration is still open and 
> the
> rates are IMHO quite reasonable: https://ifcs-isaf2020.org/registration
> If it's still too much, you can pretend you are a student. Nobody is checking
> this anyways.
> 
> -- 
> Science is made up of so many things that appear obvious 
> after they are explained. -- Pardot Kynes
> 
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Re: [time-nuts] "The Penultimate HP5065 A15"

[Bruce Griffiths]

> On 04 August 2020 at 10:32 Poul-Henning Kamp  wrote:
> 
> 
> 
> Attila Kinali writes:
> 
> >> The main reason I dont just repair/replace the A15 is that 
> >> I want to find out how much instability the PSU contributes.
> >
> >There are very few points where supply voltage (in)stability
> >contributes to long term frequency drift in a Rb vapor cell standard.
> 
> Obviously.
> 
> But it does contribute quite a lot on the sub-hour time-scale, some
> of it via temperature-dependencies.
> 
>
> >
> >For this to be a valid test, you also need to switch the
> >polarity of the light, otherwise you excite different states
> >with slightly different magnetic dependence.
> 
> "polarity of the light" - You mean the direction ?

More likely polarisation switching was intended.
eg between LH and RH circularly polarised light.
A linear polariser and a quarter waveplate are required to produce circularly 
polarised light from the unpolarised light emitted by a rubidium lamp.


Bruce

> 
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Re: [time-nuts] HP-10811AB-OCXO interface questions

[Bruce Griffiths]

For sine to square wave conversion use LTC6957 (select variant to suit 
following logic).


Bruce

> On 02 September 2020 at 17:24 Manfred Bartz  mailto:vk3...@gmail.com > wrote:
> 
> 
> Hi all,
> 
> I bought 2 x 10811 OCXOs for a 10MHz GPSDO project I am working on.
> The OCXOs came with an interface board HP 05328-20027, see attached
> pictures.
> 
> Questions:
>1. Is it worth keeping the interface board?
> 
> a. If yes, does anyone have the schematic and the data on the ICs?
> b. What is that TO220 device? and
> c. why is it mounted on a standoff on the back of the PCB?
>1. Any advice/caution on matching the OCXO output impedance?
>2. Any recommendation for a (>= 4-ch) distribution amplifier?
>3. Any advice on a low jitter comparator for further digital 
> processing,
> 
> e.g. for a 1pps signal?
> 
> Thanks and 73
> --
> Manfred VK3AES
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Re: [time-nuts] Some FTS1000 questions

[Bruce Griffiths]

You could use either the NIST CG JFET doubler or its bipolar CB equivalent.

Bruce
> On 11 September 2020 at 08:43 Tobias Pluess  wrote:
> 
> 
> Dear colleagues
> 
> I recently got a FTS1000 oscillator. (Not FTS1000A or B, but just FTS1000,
> I assume it is the first version). It is a very nice unit, but I wanted to
> know a bit more about its construction and opened it.
> After I had replaced the foam which was already quite dissolved, I began
> reverse engineering the output amplifier.
> Has someone perhaps already done that?
> I was thinking about whether it would be possible to replace the output
> amplifier with one that has an integrated doubler (as my unit is a 5MHz
> version).
> 
> BR
> Tobias
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Re: [time-nuts] What do people use for measuring temperature?

[Bruce Griffiths]

Drift ~1-2mK per year for suitably conditioned thermistors at 25C:
https://www.littelfuse.com/technical-resources/technical-centers/temperature-sensors/thermistor-info/thermistor-terminology/stability.aspx

Bruce
> On 27 September 2020 at 11:15 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> Roughly speaking 99.9% of all OCXO’s use thermistors as temperature 
> sensors. 
> The normal evaluation process on a new one *probably* would catch something < 
> 0.01C
> over a few months. You may do it a couple different ways depending on the 
> target
> OCXO. The net result is still in the “golly gee wiz low” sort of range. If 
> you can detect a 
> drift / shift, you disqualify that part and move on to another one. Very few 
> glass bead 
> parts seem to get tossed out …..
> 
> Bob
> 
> 
> 
> > On Sep 26, 2020, at 4:23 PM, John Ponsonby  wrote:
> > 
> > Have any time-nuts got any data on the long term stability or drift 
> > rates/ageing characteristics of thermistors? I am concerned with  ability 
> > of holding temperature constant at the milliK level for years. I reckon 
> > that if one can measure it one can control it. Conversely if one can't 
> > measure it, because of the instability of the sensor,  one can't control it.
> > John Ponsonby
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Re: [time-nuts] What do people use for meassuring temperature?

[Bruce Griffiths]

Here's a NIST paper on Thermistor stability:
https://ia800609.us.archive.org/2/items/jresv83n3p247/jresv83n3p247_A1b.pdf

Bruce
> On 28 September 2020 at 01:37 John Ponsonby  wrote:
> 
> 
> Bruce Griffith points to the note put out by Littelfuse. It is very meagre. 
> It says that '...thermistors can be produced with  typical drift of only 
> 0.001˚C to 0.002˚C per Year." It doesn't say that they are produced and still 
> less that Littelfuse produces them. Bruce also refers to thermistors being  
> 'Suitably conditioned at 25˚C' What is this conditioning process and what if 
> the intended working temperature is not 25˚C?. Surely more must be known 
> about this matter.
> Jeremy Nichols' questions are very apposite.
> I see that the Steinhart Hart Equation seems to be entirely empirical without 
> any underlying semiconductor theoretical foundation.
> John Ponsonby
> 
> 
> Do we know what this ?Long Term Aging Process? is or is it proprietary?
> 
> 
> 
> On Sat, Sep 26, 2020 at 5:03 PM Bruce Griffiths  <mailto:bruce.griffi...@xtra.co.nz>>
> wrote:
> 
> > Drift ~1-2mK per year for suitably conditioned thermistors at 25C:
> > 
> > 
> > https://www.littelfuse.com/technical-resources/technical-centers/temperature-sensors/thermistor-info/thermistor-terminology/stability.aspx
> >  
> > <https://www.littelfuse.com/technical-resources/technical-centers/temperature-sensors/thermistor-info/thermistor-terminology/stability.aspx>
> > 
> > 
> > 
> > Bruce
> > 
> >> On 27 September 2020 at 11:15 Bob kb8tq  >> <mailto:kb...@n1k.org>> wrote:
> > 
> >> 
> > 
> >> 
> > 
> >> Hi
> > 
> >> 
> > 
> >> Roughly speaking 99.9% of all OCXO?s use thermistors as temperature
> > sensors.
> > 
> >> The normal evaluation process on a new one *probably* would catch
> > something < 0.01C
> > 
> >> over a few months. You may do it a couple different ways depending on
> > the target
> > 
> >> OCXO. The net result is still in the ?golly gee wiz low? sort of range.
> > If you can detect a
> > 
> >> drift / shift, you disqualify that part and move on to another one. Very
> > few glass bead
> > 
> >> parts seem to get tossed out ?..
> > 
> >> 
> > 
> >> Bob
> > 
> >> 
> > 
> >> 
> > 
> >> 
> > 
> >>> On Sep 26, 2020, at 4:23 PM, John Ponsonby  >>> <mailto:jebponso...@gmail.com>>
> > wrote:
> > 
> >>> 
> > 
> >>> Have any time-nuts got any data on the long term stability or drift
> > rates/ageing characteristics of thermistors? I am concerned with  ability
> > of holding temperature constant at the milliK level for years. I reckon
> > that if one can measure it one can control it. Conversely if one can't
> > measure it, because of the instability of the sensor,  one can't control it.
> > 
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Re: [time-nuts] What do people use for measuring temperature?

[Bruce Griffiths]

If one does a ratiometric measurement comparing the voltage drop across the RTD 
with the voltage drop across a stable low Tc resistor connected in series with 
the RTD the excitation source only needs to be quiet with good short term 
stability.

Bruce

> On 29 September 2020 at 07:48 "John Moran, Scawby Design" 
>  wrote:
> 
> 
> Thanks for going easy on me Bob ... a case of more haste, less speed! I 
> focussed on low long-term drift specs without realising I had turned up a 
> voltage reference, sorry.
> 
> However, I have found some YSI glass encased thermistors that have long-term 
> drift specs of <10mK at 25C and 75C over a period of 100 months. They are in 
> the YSI 46000 series - data sheet attached.
> 
> http://www.farnell.com/datasheets/169207.pdf
> 
> There is an interesting paper by NIST on achieving the International 
> Temperature scale - link attached (it is 196 pages and 10MB) that seems to 
> indicate platinum sensors are the most stable at less than 1mK and, of 
> course, to be able to measure these resistors accurately, you need an equally 
> low-drift voltage/current source. :-)
> 
> https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote1265.pdf
> 
> This reference appeared from an EEVblog where I think some Volt-nuts were 
> discussing temperature. One of them confirmed that the most economical way 
> was to have a group of lower-cost sensors and characterise them.
> 
> https://www.eevblog.com/forum/metrology/long-term-stability-of-temperature-sensors/
> 
> John 
> 
> 
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Re: [time-nuts] SMPS or conventional?

[Bruce Griffiths]

If the drive current ripple is too high fatigue failure from cyclic 
thermomechanical stress can be significant.

Bruce
> On 23 October 2020 at 10:37 ed breya  wrote:
> 
> 
> Regarding TEC life, in my experience, what wrecks them the most is 
> cooling applications where the cold side is below the dew point, and 
> water condenses out onto and into the TEC Peltier array. This eventually 
> rots the elements from corrosion and electrolysis, until something craps 
> out. If the TEC will be exposed to ambient air, and run below or even 
> near the expected dew point, the sides should be sealed up with silicone 
> goop for longer life. Even then, it's not foolproof, since it will never 
> be a perfect seal.
> 
> If the TEC is in a closed, benign environment or vacuum, then it should 
> last indefinitely, unless abused power-dissipation-wise, or mechanically 
> by thermal stress. When the temperature cycles, the whole part must be 
> allowed to change dimensions slightly, so the mounting needs to have 
> some compliance.
> 
> Ed
> 
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Re: [time-nuts] OCXO housings - Why copper and not iron/steel?

[Bruce Griffiths]

Not true 
The Wiedemann-Franz gives the ratio of the thermal conductivity to electrical 
conductivity of a metal:
( pi^2 / 3 ) * ( (k/e)^2 ) * T

Bruce
> On 31 October 2020 at 12:49 "Dr. David Kirkby" 
>  wrote:
> 
> 
> On Fri, 30 Oct 2020 at 22:17, Luiz Alberto Saba  wrote:
> 
> > My bad... copper is the second, losing only to silver, as a thermal
> > conductor.
> >
> 
> I think you are mistaken.  Copper is second to silver for *electrical*
> conductivity, but I doubt that is so for thermal conductivity. I think
> diamond, which is a form of carbon, is the best thermal conductor, and
> around 5x better than copper.
> 
> Dave
> 
> -- 
> Dr. David Kirkby,
> Kirkby Microwave Ltd,
> drkir...@kirkbymicrowave.co.uk
> https://www.kirkbymicrowave.co.uk/
> Telephone 01621-680100./ +44 1621 680100
> 
> Registered in England & Wales, company number 08914892.
> Registered office:
> Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
> Kingdom
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Re: [time-nuts] Flicker Noise Reduction

[Bruce Griffiths]

Its just another variation on the principle of the Dicke radiometer.
In their case the amplifier input device is turned off periodically by 
modulating its gate bias.
https://www.engr.colostate.edu/ece/faculty/reising/pdf/journals/Ogut_et_al_T-TST_2020.pdf

Bruce

> On 19 November 2020 at 12:38 Attila Kinali  wrote:
> 
> 
> On Wed, 18 Nov 2020 19:13:00 + (UTC)
> Bruce Hunter via time-nuts  wrote:
> 
> > Can anyone who subscribes to these transactions report on this?  I dropped 
> > my subscription.
> > In this letter, a novel 1/f noise mitigation technique is presented to 
> > improve the receiver 1/f noise performance of a 670 GHz receiver. 
> 
> The paper in question is:
> "A Novel 1/f Noise Mitigation Technique Applied to a 670 GHz Receiver",
> by Ogut et al.
> https://doi.org/10.1109/TTHZ.2020.3036179
> 
> The description is extremely vague, but I think what they are doing
> is modulating the gain of the first LNA stage in an amplifier chain
> to get information on the total gain of the chain and correct for it.
> Which would make it basically a fancy chopper-amplifier that operates
> on the gain instead of the offset voltage.
> 
>   Attila Kinali
> 
> -- 
> The driving force behind research is the question: "Why?"
> There are things we don't understand and things we always 
> wonder about. And that's why we do research.
>   -- Kobayashi Makoto
> 
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Re: [time-nuts] Flicker Noise Reduction

[Bruce Griffiths]

Attached is the block diagram of the receiver in essence an amplifier for which 
the effective input is gated/chopped on and off by turning the amplifier input 
FET on and off.

Bruce
> On 19 November 2020 at 16:15 "Richard (Rick) Karlquist" 
>  wrote:
> 
> 
> 
> On 11/18/2020 5:27 PM, jimlux wrote:
> 
> > The proposed mitigation technique relies on tracking the
> > rapid gain variations in the radiometer due to 1/f noise and
> > correcting them by generating a baseline state in the first
> > amplification stage of the low noise amplifier (LNA). The
> > proposed 1/f noise mitigation method can be applied to any
> > receiver, but it is especially valuable for THz receivers since
> 
> I'm confused here.  My understanding of 1/f noise was
> that it was additive as in "AWGN".  Can you clarify this?
> You also imply it works for ANY receiver.  Now I'm REALLY
> confused.  Unless the "direct conversion receiver" is actually
> an envelope detector.  Then I think I see how it can work
> at any frequency.
> 
> Not arguing, just trying to understand :-)
> 
> Thanks.
> 
> Rick N6RK
> 
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Re: [time-nuts] SMPS or conventional?

[Bruce Griffiths]

Original source about TEC lifetime reduction when the TEC ripple cureent is 
high:
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1991-02.pdf
Page 74
I suspect that someone there may have been bitten by the short TEC life 
experienced without the LC filter. 
Although they used relatively small TECs the size of the individual Peltier 
element is the determining factor for the ripple current frequency dependence 
of TEC life. HP used a 40kHz PWM frequency.

There should be a relatively uniform temperature gradient along the length of 
each Peltier element.

TEC module datasheets are generally silent on the effect of ripple current on 
TEC lifetime.

CUI merely indicate that keeping the TEC ripple current below 5% ensures that 
TEC performance is maximised.

Peltier element solder junctions to the ceramic endplates usually fail after 
3000 cycles or therabouts.
CUI use a compliant thermally conductive adhesive to achieve a longer cycle 
life.
Bruce
> On 22 December 2020 at 12:43 Hal Murray  wrote:
> 
> 
> [Old mail, context is TECs]
> 
> bruce.griffi...@xtra.co.nz said:
> > If the drive current ripple is too high fatigue failure from cyclic
> > thermomechanical stress can be significant. 
> 
> Do good data sheets say anything about that?
> 
> Is there a frequency term in there?  Can I use PWM, which is as much ripple 
> as 
> you can get, as long as the frequency is high enough?  If yes, ballpark of 
> how 
> high?
> 
> Physically, where is the heat/cold generated?  Is it mostly at the junction?
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] TECs in cooling below ambient

[Bruce Griffiths]

You could always use a TEC as the heart of a dewpoint sensor by optically 
sensing the temperature required for dew to form on a cooled mirror.
In practice the temperature at which the dew vanishes is typically used.
A collimated light beam together with a photodiode is typically used to sense 
the presence of dew droplets on the mirror.

Bruce
> On 24 December 2020 at 08:57 ed breya  wrote:
> 
> 
> This recent TEC talk reminded of some of my long term planned projects, 
> and related issues. I have at least four "someday" projects involving 
> TECs, to regulate device temperatures near or below "normal" room 
> temperature, including a high precision DC voltage standard, a sub-fA 
> electrometer circuit, a constant temperature block for nonlinear analog 
> computing elements, and a small general purpose heat/cool box for device 
> and circuit testing. Each has its own particular system, application, 
> and environment issues, but common to all is the lower limit of running 
> temperature, based on the local climate conditions and dew point. I plan 
> to estimate the lowest possible operating temperatures for expected 
> conditions, that avoids condensation, and not having to resort to 
> special packaging.
> 
> An essential thing for this is a dew point calculator. I found lots 
> online, but this is my favorite so far. It's slider-based, so you don't 
> even have to enter numbers.
> 
> http://www.dpcalc.org/
> 
> The harder part is finding the normal range of local climate conditions.
> 
> Ed
> 
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Re: [time-nuts] TECs in cooling below ambient

[Bruce Griffiths]

The method still appears to be in use:
http://www.michell.com/nl/documents/Optidew_Vision_97144_NL_Datasheet-V6.pdf

Bruce
> On 24 December 2020 at 14:37 Dana Whitlow  wrote:
> 
> 
> The optical sensing of despoint by dew-on-the-mirror was used in a device
> designed
> at the Whirlpool Research labs in St. Joseph, MI.  It apparently never made
> it into
> production, but a number of units were built and sold or given away (I'm
> not sure).
> I know about this because I interned at the lab during college summer
> breaks, and
> on one occasion I was asked to replace the Peltier (TEC) module in one of
> these
> units.  These units had a thermocouple buried under the cold mirror's
> surface, and
> use of the device required that the user provide the instrument to read the
> thermo-
> couple's temperature.
> 
> I've long wondered how this system dealt with the fact that the desired
> operating
> point of the loop is on a sharp corner of the light versus temperature
> curve where
> dew is just beginning to form, and there is no "negative dew" on the warm
> side of
> that point.  I hadn't thought of this complication when I was working with
> this thing,
> however, or I would have asked.  Oh, well, an opportunity missed.  Sigh!
> 
> Dana
> 
> 
> On Wed, Dec 23, 2020 at 6:53 PM Bruce Griffiths 
> wrote:
> 
> > You could always use a TEC as the heart of a dewpoint sensor by optically
> > sensing the temperature required for dew to form on a cooled mirror.
> > In practice the temperature at which the dew vanishes is typically used.
> > A collimated light beam together with a photodiode is typically used to
> > sense the presence of dew droplets on the mirror.
> >
> > Bruce
> > > On 24 December 2020 at 08:57 ed breya  wrote:
> > >
> > >
> > > This recent TEC talk reminded of some of my long term planned projects,
> > > and related issues. I have at least four "someday" projects involving
> > > TECs, to regulate device temperatures near or below "normal" room
> > > temperature, including a high precision DC voltage standard, a sub-fA
> > > electrometer circuit, a constant temperature block for nonlinear analog
> > > computing elements, and a small general purpose heat/cool box for device
> > > and circuit testing. Each has its own particular system, application,
> > > and environment issues, but common to all is the lower limit of running
> > > temperature, based on the local climate conditions and dew point. I plan
> > > to estimate the lowest possible operating temperatures for expected
> > > conditions, that avoids condensation, and not having to resort to
> > > special packaging.
> > >
> > > An essential thing for this is a dew point calculator. I found lots
> > > online, but this is my favorite so far. It's slider-based, so you don't
> > > even have to enter numbers.
> > >
> > > http://www.dpcalc.org/
> > >
> > > The harder part is finding the normal range of local climate conditions.
> > >
> > > Ed
> > >
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Re: [time-nuts] Holiday Hydrogen Glow!

[Bruce Griffiths]

The Hydrogen plasma emission is dominated in the visible dominated by Halpha 
emission at 656.3 nm. Other Balmer series lines will also be present.

Bruce
> On 26 December 2020 at 09:12 Magnus Danielson  wrote:
> 
> 
> Dana,
> 
> The glow is a side-effect of the plasma. The primary use in H-maser is
> to split H2 gad into separate H atoms before sent through a
> state-separating hexapole magnet, known as A-field magnet.
> 
> In Rubidium oscillators, you achieve the same plasma glow, but then it
> is the D-line emission which is the primary goal, where the D1 and D2
> lines is dominant and one of them is filtered.
> 
> For hydrogen, the D-line is way up in 121,6 nm rather than 794 nm and
> 780 nm of rubidium, so it's not the D-line glow we see from the hydrogen
> atom.
> 
> So, the same glow have separate uses and mechanisms.
> 
> Cheers,
> Magnus
> 
> On 2020-12-25 20:08, Dana Whitlow wrote:
> > It appears that the pink glow is reaching at least several inches from
> > the discharge region.  Am I correct in thinking that it stems from
> > recombination of electrons and protons into neutral atome?  And
> > regardless of the precise mechanism, do any significant number
> > of the glow-causing species make it through the state selector into
> > the storage bulb?  I'm wondering if one could peek into the microwave
> > cavity through a small aperture and see a glow from the storage bulb
> > itself.
> >
> > Dana
> >
> >
> > On Fri, Dec 25, 2020 at 12:13 PM  wrote:
> >
> >> And here is an EFOS2 Maser glow.
> >>
> >> Happy holidays, and Merry Christmas!
> >>
> >> Corby___
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Re: [time-nuts] clocks for amateur radio and astronomy (was: World's most precise.... wall clock)

[Bruce Griffiths]

Unless something akin to VLBI or pulsar timing is involved millisecond accuracy 
will usually suffice for amateur astronomy.

Bruce
> On 11 March 2021 at 06:31 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> > On Mar 10, 2021, at 12:17 PM, Attila Kinali  wrote:
> > 
> > On Wed, 10 Mar 2021 06:39:46 -0800
> > "Charlie"  wrote:
> > 
> >> My question is thus: It seems that procuring a more precise PPS/time output
> >> unit is quite a bit more costly than what I have; even more costly is a 
> >> unit
> >> that has both more precise PPS/time output,
> > 
> > The question is more whether it is good enough. How accurate
> > do you need your time? How precise does it need to be?
> > If the answer to both questions is smaller than 100ns,
> 
> I suspect that’s a typo. “larger than 100 ns” ( 1 us > 100 ns ….) 
> would seem to be the correct way to look at it. 
> 
> > then you
> > are good with anything you can get your hands on, even the cheapest
> > GPS receiver. If you need better than that, you need to look
> > more closely and calculate each contributor to uncertainty,
> > both random and systematic and see where you can and want to
> > improve (or compromise).
> > 
> > 
> >> and a really stable 10 Mhz
> >> output ( I might add that I am a Ham, where 1 uhz  error is detrimental).
> > 
> > At what time scales you need that 1µHz stability? Is it for
> > a few seconds? Or over a few hours? How accurate does it have
> > to be?
> > And are you sure it is really 1µHz @ 10MHz? Because that's
> > a stability better than 1e-13. Which isn't something most people
> > just have in their lab. You need a an exceptionally good OCXO to
> > reach down there (an OCXO that costs you as much as a car)
> > and even those reach it only over a very limited τ between
> > about 1s and maybe 100s. Beyond a τ of 1000s you have the option
> > of using a HP5065, possibly with Corby's Super-HP6065 modifications.
> > Even GPS takes until somwhere like 100ks to reach down to 1e-13.
> 
> Even crazier if you are talking about your transmit frequency at VHF :) :).
> Welcome to why Hz, uHz, etc normally are replaced with ppm, ppb, and
> the like … That’s been the case in every place I’v ever worked on this stuff. 
> 
> Bob
> 
> > 
> > If you need better than that, either at shorter or longer τ,
> > then we are clearly deep in atomic clock territory. Either
> > hydrogen maser. caesium beam standard or cold atomic clock.
> > 
> > Attila Kinali
> > -- 
> > The driving force behind research is the question: "Why?"
> > There are things we don't understand and things we always 
> > wonder about. And that's why we do research.
> > -- Kobayashi Makoto
> > 
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[time-nuts] Re: Best frequency to start for GHz synth ?

[Bruce Griffiths]

An interferogram showing the nodes etc. of such a resonating quartz crystal 
ring was posted by me in either February or March 2020.

Bruce 
> On 01 April 2021 at 15:16 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> Some of the early 100 KHz resonators were ring shaped. The British really 
> pioneered 
> this side of things ( while the US was still doing bars …) back in the 
> 1930’s. AFIK the
> mode is not a whispering gallery. 
> 
> Given the low frequency of a 100 KHz resonator, a “not space limited” design 
> might get
> to some pretty insane Q values. Meter level dimensions probably would be 
> involved.
> Good luck sourcing the raw quartz :) :) :) ( …. and yes, that’s only the 
> first of a long list
> of issues ….).
> 
> Bob
> 
> > On Mar 31, 2021, at 3:23 PM, Poul-Henning Kamp  wrote:
> > 
> >> If you were going insane on a fountain, you likely would go with one of 
> >> the 
> >> sapphire whispering gallery devices as the start of your chain. A good one
> >> will blow a quartz crystal based part away ….
> > 
> > That reminds me:
> > 
> > I think the first quartz-crystal at Bell Labs was ring-shaped, do you know 
> > if that used a whispering gallery vibration mode ?
> > 
> > 
> > -- 
> > Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> > p...@freebsd.org | TCP/IP since RFC 956
> > FreeBSD committer   | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by incompetence.
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[time-nuts] Re: Best frequency to start for GHz synth ?

[Bruce Griffiths]

Poseidon Scientific Instruments (acquired by Raytheon) make a room temperature 
10.24GHz Sapphire loaded cavity oscillator with a low PN floor:
https://www.rdi.uwa.edu.au/__data/assets/pdf_file/0012/3447669/Raytheon-TechnologyToday-20141-Extract.pdf

Bruce 
> On 02 April 2021 at 05:06 Chris Caudle <6807.ch...@pop.powweb.com> wrote:
> 
> 
> On 2021-03-31 14:27, Richard (Rick) Karlquist wrote:
> > When I left Keysight in 2014, they were still trying to solve the
> > microphonic problem in their sapphire resonator oscillator.  Also,
> > it is still necessary to lock the oscillator to a 5 or 10 MHz
> > OCXO.  The oscillator is tuned by varying its oven temperature
> > set ppoint.
> 
> What kind of oven temperature range?  I thought sapphire oscillator was 
> pretty much synonymous with "cryogenic sapphire oscillator."  I found a 
> paper which described sapphire as a "low loss material with loss tangent 
> of 5×10^−6 at room temperature, 2×10^−8 at 77 K and 7×10^−10 at 4 K 
> giving Q-values of more than >10^7 at low temperatures."
> 
> That paper seemed to be describing some kind of temperature compensation 
> they  had developed to reduce the temperature sensitivity of 10ppm/K and 
> also move the turnover point from 77K to 92K.  92K isn't exactly what I 
> think of when I hear "oven" so presumably there is some mode that works 
> at around 300K that I didn't find discussed yet.
> 
> -- 
> Chris Caudle
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[time-nuts] Re: Best frequency to start for GHz synth ?

[Bruce Griffiths]

The oscillator circuit consists of an SSM2210 supermatch npn pair configured as 
a long-tailed differential pair with a 12mA tail current and 51 ohm collector 
loads. One output feeds the output buffer whilst the other provides feedback to 
the crystal via an LC network that is series resonant at 10MHz and parallel 
resonant at 10.9MHz followed by a varactor tuned phase shift network connected 
to one end of the SC cut crystal.
The other end of the crystal drives the input of the diffamp via an RF step up 
transformer (ADT16-6T) with a grounded secondary centre tap.

Bruce  
> On 03 April 2021 at 01:36 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> Unfortunately, even the numbers he quotes are going to be less than 
> ideal if multiplied directly to 10 GHz. Will they be “good enough” for 
> this or that? As always … that depends. It is rare to find any piece 
> of commercial gear that does it that way.
> 
> Bob
> 
> > On Apr 2, 2021, at 4:38 AM, John Moran, Scawby Design 
> >  wrote:
> > 
> > Since low phase noise seems to be a main requirement here, this paper by 
> > Jeremy Everard from York University may be of interest -
> > 
> > 'Ultralow Phase Noise 10-MHz Crystal Oscillators'
> > 
> > Available here -
> > 
> > https://ieeexplore.ieee.org/document/8540461
> > 
> > It also shows construction of a double oven system for it.
> > 
> > I believe Jeremy was working on sapphire oscillators 20 years ago when I 
> > worked at York for a while.
> > 
> > John 
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Re: [time-nuts] Low phase noise affordable GPSDO

[Bruce Griffiths]

The PN of the output amplifier in the thunderbolt will limit the PN nois of the 
10Mhz output to a value significantly higher than the actual PN at the output 
of a low PN OCXO.

Bruce

> On 21 June 2018 at 09:26 Attila Kinali  wrote:
> 
> 
> On Wed, 20 Jun 2018 14:27:35 +
> Ethan Waldo  wrote:
> 
> > I've tried my best to scan through the archives to see if this has already
> > been answered, so apologies if I missed something relevant.  I am going to
> > be experimenting with >10Ghz microwave frequency grounded coplanar waveguide
> > phase combining/cancellation/detection across a number of generated
> > signals.  That being said, I am in the market for a GPSDO that has the least
> > amount of phase noise.
> 
> Phase noise is usually not the strong traits of GPSDOs.
> That said, I guess a Trimble Thunderbolt or Nick Sayer's GPSDO with
> the OCXO option would probably fit your bill.
> 
> Alternatively, take any of those two GPSDO and replace the OCXO
> by one that has as low phase noise as you need.
> 
> 
> > A secondary factor in my choice is how many 10Mhz references the GPSDO
> > can provide to sync all my signal generators; not as concerned about what
> > amplitude is provided.
> 
> You are looking a bit naively at this. The noise floor of modern,
> low-noise OCXO is limited by the Johnson noise of the 50R impedance.
> Ie the higher the output signal level, the lower the noise floor (in dBc).
> Hence, just using some passive splitters will increase your noise
> levels. The 1/f^a noise levels are unaffected by this, though. 
> 
> I would recommend going for a seperate distribution amplifier in order
> to keep the noise at a minimum. If you are fine with DIY, go for the 
> design by Anders Wallin.
> 
> 
>   Attila Kinali
> -- 
>   The bad part of Zurich is where the degenerates
> throw DARK chocolate at you.
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Re: [time-nuts] HP 5065A A1 replacement with DDS

[Bruce Griffiths]

In principle DDS spurs due to phase truncation can be largely suppressed using 
well known techniques when an FPGA is used just leaving spurs due to the DAC.

Bruce

> On 25 June 2018 at 06:00 Attila Kinali  mailto:att...@kinali.ch > wrote:
> 
> 
> On Sun, 24 Jun 2018 17:29:43 +
> "Poul-Henning Kamp" mailto:phk@phk.freebsd .dk> wrote:
> 
> > > My plan is to replace the entire chain up to the 60 MHz with that
> > DDS, and do the modulation digitally, then put one of those
> > "geophone/optical" 24bit ADC's on the photo-sensor and close the 
> > loop.
> > 
> > > I recently thought about that problem and came up with a solution
> that might replace more than just A1:
> 
> The idea is to use an FPGA (can be a relatively small one) as an I/Q DDS,
> then use an I/Q modulator shift the frequency into the right spot
> and supressing the mirror. The advantage of using an FPGA instead of
> an off the shelf DDS comes from that it makes it possible to connect
> an ADC to it, which samples the photo diode voltage and do the 
> demodulation
> and integration in the digital domain, thus incuring less noise and zero
> drift. Additionally, adding another DAC to generate the 10MHz or any
> other frequency directly, gives the possibility to tune the Rb output
> in a very wide range without incuring any problems with synthesis chain
> and decoupling the reference from the Rb (ie the reference doesn't even
> need to be tunable).
> 
> Attached is the page of my notebook with the schematic of the idea.
> (sorry for the bad handwriting). The components that are not labled
> are: PLL: any that can work with the Ref input, e.g. ADF4001.
> The VCXO is an ABLJO or any equivalent with 155.52MHz or 156.25MHz.
> The divider is a D-FF, either an 74LVC74A or better NB7V52M.
> The output frequency of the DDS is in the range of 11-18MHz,
> depending on the output frequency and the VCXO frequency.
> 
> 
> Attila Kinali
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] TNS-BUF order update

[Bruce Griffiths]

Its a form  of CE with a resistor in series with the emitter coupled with 
transformer feedback from collector to base.
Production scheduling likely prevents substitution of alternatives to achieve a 
faster delivery.
Assembly costs would likely increase if leaded parts are substituted.

Initial breadboards of a single amplifier stage used leaded components for 
convenience.

Bruce

> On 26 June 2018 at 11:19 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> If it’s used in a grounded base configuration, it does indeed matter …..
> 
> Bob
> 
> > On Jun 25, 2018, at 6:39 PM, Dana Whitlow  wrote:
> > 
> > John speaks of high dissipation, which is a good point.  However, I doubt
> > that the
> > lead inductance will be a noticeable factor at 10 MHz unless a leaded part
> > is
> > mounted sloppily.
> > 
> > Dana
> > 
> > 
> > On Mon, Jun 25, 2018 at 4:04 PM, Bob kb8tq  wrote:
> > 
> >> Hi
> >> 
> >> The PZT version actually has a higher power dissipation than the leaded
> >> part. It
> >> also does a bit better at RF frequencies due to lower lead inductances.
> >> Not having
> >> the schematic in front of me, I don’t know if either one is a real big
> >> deal in this case.
> >> It has been on other circuits I’ve used them in.
> >> 
> >> Bob
> >> 
> >>> On Jun 25, 2018, at 4:56 PM, Dana Whitlow  wrote:
> >>> 
> >>> John,
> >>> 
> >>> Couldn't the TO-92 part (2N3904) be soldered down instead (if one has
> >>> steady hands),
> >>> and work about as well?
> >>> 
> >>> Dana
> >>> 
> >>> 
> >>> On Mon, Jun 25, 2018 at 11:58 AM, John Ackermann N8UR 
> >> wrote:
> >>> 
>  To those who pre-ordered TNS-BUF boards:
>  
>  We've had a delay due to parts availability -- a common transistor
>  (PZT3904) is apparently on worldwide back order with lead times quoted
> >> of
>  up to a year.  Our contract manufacturer has finally found a source, but
>  they will not be delivered until mid-August.  That means that TAPR won't
>  receive the boards until the second half of September.
>  
>  If the delay causes you a problem and you'd like to cancel your order,
>  please contact the TAPR office (taproff...@tapr.org) and John will take
>  care of that (though he will be out of town until July 6).
>  
>  Sorry for the inconvenience, but we did not want to risk using a
>  substitute component that might change the performance of the unit.
>  
>  John
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Re: [time-nuts] Question about effect of spurious frequency modulation on Allan Deviation

[Bruce Griffiths]

Surely all that's required is a simplistic worst case analysis.
Just assume that the value of Tau is always the worst possible so the full 
effect of the modulation is always seen.

If the worst case phase modulation is say phi

then the worst case ADEV (Tau) will be proportional to phi*T/Tau
where T is the nominal signal period.

i.e. ADEV(Tau) < constant*phi*T/Tau

Bruce
> On 07 August 2018 at 10:37 "Richard (Rick) Karlquist"  
> wrote:
> 
> 
> The discussion has gotten off track.
> I probably didn't make myself clear.
> 
> When I talked about cleaning up the signal, I meant
> exactly that, cleaning up the signal using a filter.
> As opposed to cleaning up the measurement after the
> fact.  I just need to know how well I need to filter
> the signal to meet a certain ADEV measurement level.
> 
> The FM I have is not "slow".  The rate
> is in the MHz range.  Can Stable 32 simulate that?
> 
> Again, this is analogous to the 5071A having 1 MHz
> spurs of about -90 dBc, yet the ADEV is not much
> different than an open loop 10811.  How high would
> the 1 MHz spurs have to be to affect ADEV?
> 
> Thanks.
> 
> Rick
> 
> On 8/6/2018 1:56 PM, Tom Van Baak wrote:
> >> If you know the *source* of the bias you're trying to remove (i.e. you
> >> know it's a sinusoidal frequency modulation), I don't know that it's any
> >> different than removing long term drift.
> > 
> > The TimeLab 'n' command (apply notch filter to phase records) is 
> > specifically for this purpose. JohnM added it when he ran into an H-maser 
> > which suffered from some sort of consistent periodic modulation. It spoiled 
> > the ADEV plots, but it did so in a deterministic manner. In a case like 
> > this you either debug the root cause of the h/w problem and make the 
> > repair, or just "repair it" in s/w. Like you say, it's the same concept 
> > (and danger) as removing linear drift or other deterministic / model-able 
> > effects.
> > 
> > To explore this for yourself, you can use Stable32 to generate synthetic 
> > phase/frequency data with your choice of noise and modulation. Then use 
> > TimeLab to view the raw data and to apply the notch filter.
> > 
> > I've written up some quick examples here: www.leapsecond.com/pages/adev-fm/
> > 
> > The plots dramatically show what effect slow FM can have on an ADEV plot. 
> > It also shows how well the TimeLab notch filter works. If you don't have 
> > time to look at that page, I've attached one plot to whet your appetite.
> > 
> > /tvb
> > 
> > 
> > 
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Re: [time-nuts] TNS-BUF update

[Bruce Griffiths]

Rick

I devised the bias circuit for the TNS-BUF.
It exploits the fact that for a RED LED at least the difference between the LED 
forward voltage and the transistor Vbe is ~ 1V and has a fairly low tempco and 
has low noise (at  least for RED LEDs). 
(Most of the LTSpice LED models do not correctly predict LED forward voltage 
drop tempco.)

Most classical  schemes for biasing BJTs use a resistive voltage divider which 
inevitably couples power supply noise into the BJT collector current.

John Miles changed the bias circuit of some classical series shunt amp buffers 
to one similar to this and the buffer flicker phase noise was significantly 
reduced.

In principle an LED could be used to directly set the dc bias at the base of 
the amplifier transistors, however inductors may be required to shunt part of 
the emitter series resistance at dc to allow the desired dc collector current 
to be established. A pair of series connected LEDs buffered by an npn emitter 
follower would allow the bias voltage to be shared by all stages and allow the 
inductor to be replaced by a capacitor bypassing part of the emitter to ground 
resistance required to establish the desired collector current whilst achieving 
the required resistance from RF to ground for RF. 

Classical bias schemes are usually much noisier especially at low frequencies. 
Even regulators like the LT3042 are quite noisy at frequencies below the the 
pole of the reference circuit low pass filter.

One requirement was operation from a standard not necessarily ultra low noise 
power supply.
Sensing and controlling the collector current has the advantage of simplifying 
the emitter to ground network to a single series resistor.
This emitter series resistor also suppresses parasitic oscillations somewhat 
above 100MHz possibly due to feedback transformer parasitics.  

Bruce

> On 19 August 2018 at 15:31 "Richard (Rick) Karlquist"  
> wrote:
> 
> 
> I was reverse engineering the circuit so I could verify
> that the high power transistors are used in the amplifier,
> and the low power ones are bias controllers.  The bias
> circuit resembles the ones used for applications where
> the transistor's emitter is connected directly to ground
> to reduce parasitic inductance at microwave frequencies.
> But this is 10 MHz and in any event, there is a 68 ohm
> unbypassed emitter resistor, which I assume is there to
> reduce flicker noise, which is indeed very low.
> 
> Anyway, since there is this 68 ohm resistor,
> I don't see why it isn't sufficient to simply
> connect a fixed bias of about 1V to the base.  You
> could even temperature compensate the voltage
> with a temperature sensing diode to cancel
> out drift of the base-emitter voltage.  I'm not
> saying the circuit won't work, I just suggesting it
> is needlessly complicated.
> 
> Can anyone clarify this?
> 
> Can I make a high power version of this by
> simply changing to 2N3566/2N5109/2N5943, etc.
> transistors?
> 
> Is the transformer feedback a poor man's Norton
> amplifier scheme?
> 
> 
> Rick N6RK
> 
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Re: [time-nuts] TNS-BUF update

[Bruce Griffiths]

Norton CB transformer feedback amps are quiet but they have low reverse 
isolation.

I've used that bias scheme with 2N5943's in the circuit using a 3 winding 
transformer with one winding in the collector one in the emitter circuit 
(driven via a series resistor) and one driving the load.

Series shunt feedback circuits can be quiet but have poor reverse isolation.
However if a transformer driving the load is used between the collector and the 
feedback circuit collector node the reverse isolation is improved significantly 
and the amplifier is a bit quieter than an amplifier with the same gain just 
using a collector load transformer and an emitter series resistor.

Bruce

> On 19 August 2018 at 20:48 Charles Steinmetz  wrote:
> 
> 
> Rick wrote:
> 
> > The bias
> > circuit resembles the ones used for applications where
> > the transistor's emitter is connected directly to ground
> 
> This is often called a "wrap-around" bias circuit.
> 
> > since there is this 68 ohm resistor,
> > I don't see why it isn't sufficient to simply
> > connect a fixed bias of about 1V to the base.  You
> > could even temperature compensate the voltage
> 
> > I'm not
> > saying the circuit won't work, just suggesting it
> > is needlessly complicated.
> 
> That is more or less correct, although see below re: noise.
> 
> The wrap-around circuit creates an approximately temperature-compensated 
> current with an LED, the bias transistor, and the bias transistor's 
> emitter resistor.  This current runs through a 1k resistor to ground to 
> generate an approximately temperature-compensated voltage that is used 
> to set the amplifier transistor's base voltage.
> 
> That said, the amplifier transistors run quite hot, particularly the 
> last one, which operates at about 30mA -- nowhere near the much lower 
> temperature of the LEDs and bias transistors -- so the temperature 
> compensation does not really do much to stabilize the amplifier current 
> (note that the same would be true of your posited ~1v voltage source, 
> even if it were temperature-compensated).  The wrap-around circuit *is* 
> relatively quiet, so your voltage source would likely need to be at 
> least as complicated to match its bias noise.
> 
> > Can I make a high power version of this by
> > simply changing to 2N3566/2N5109/2N5943, etc.
> > transistors?
> 
> In principle, yes.  However, note that the maximum DC current rating for 
> the specified transformers is 30mA.  For more power, you would almost 
> certainly want to pass more quiescent current through the amplifiers. 
> You would need a different transformer at least for the third stage, 
> since that stage already draws about 30mA.
> 
> > Is the transformer feedback a poor man's Norton
> > amplifier scheme?
> 
> It is a so-called "noiseless feedback" circuit, yes.
> 
> Best regards,
> 
> Charles
> 
> 
> 
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Re: [time-nuts] TNS-BUF update

[Bruce Griffiths]

The LT3042 is still inherently very noisy at ultra low frequencies approaching 
and below the pole frequency (can be well below 1Hz) of the reference filter 
(There's a limit to the maximum capacitance available/feasible). Forward biased 
diodes including LEDs are quieter in this region.

Bruce
 
> On 19 August 2018 at 23:51 Gerhard Hoffmann  wrote:
> 
> 
> 
> 
> Am 19.08.2018 um 10:22 schrieb Bruce Griffiths:
> > Rick
> >
> > I devised the bias circuit for the TNS-BUF.
> > It exploits the fact that for a RED LED at least the difference between the 
> > LED forward voltage and the transistor Vbe is ~ 1V and has a fairly low 
> > tempco and has low noise (at  least for RED LEDs).
> > (Most of the LTSpice LED models do not correctly predict LED forward 
> > voltage drop tempco.)
> >
> > Most classical  schemes for biasing BJTs use a resistive voltage divider 
> > which inevitably couples power supply noise into the BJT collector current.
> >
> > John Miles changed the bias circuit of some classical series shunt amp 
> > buffers to one similar to this and the buffer flicker phase noise was 
> > significantly reduced.
> >
> > In principle an LED could be used to directly set the dc bias at the base 
> > of the amplifier transistors, however inductors may be required to shunt 
> > part of the emitter series resistance at dc to allow the desired dc 
> > collector current to be established. A pair of series connected LEDs 
> > buffered by an npn emitter follower would allow the bias voltage to be 
> > shared by all stages and allow the inductor to be replaced by a capacitor 
> > bypassing part of the emitter to ground resistance required to establish 
> > the desired collector current whilst achieving the required resistance from 
> > RF to ground for RF.
> Not all red LEDs are created equal. For noise, by far the best I have found
> is the HLMP6000 by HP / Avago / Whoever_owns_it_today.
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24354944411/in/album-72157662535945536/
>  
>    >
> 
> 0 dB is 1nV/rtHz, +20 dB is 10 nV/rtHz and so on.
> LEDs are ineffective photo cells, probably because of the large band gap and
> their built-in color filter. I have given up to apply the blob of black 
> laquer,
> I have never seen a difference.
> 
> What I find impressive is the noise performance of low voltage Z-Diodes.
> We are always told that Zeners are noisy. No. Avalanche breakdown is noisy.
> Take a look at these NXP BZX84C2V7 and C3V3. Admire the low 1/f corner
> and note how things turn bad when we approach 5V.
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24411798996/in/album-72157662535945536/
>  
>   >
> 
> The precious 7V LM399 reference is a complete joke in comparison.
> Its oven is no help here.
> 
> > Classical bias schemes are usually much noisier especially at low 
> > frequencies. Even regulators like the LT3042 are quite noisy at frequencies 
> > below the the pole of the reference circuit low pass filter.
> That does no justice to the LT3042. It features 2nV/rtHz to _very_ low 
> frequencies.
> It is very easy to bypass a constant current source while it is very 
> costly to filter
> a low impedance LED. The LT3042 even has a startup circuit so that it 
> does not
> take forever to get to the right voltage. Most LEDs are much worse, and 
> especially
> at low frequencies.
> 
> The LT3042 is a piece of art. It leaves the rest of the regulators that 
> we know
> in the dust, by 40 dB or better.
> 
> Most of the noise < 50 Hz or so goes on my 89441A and the too-small input
> coupling capacitor of my preamp. (20 ADA4898 op amps in par, 220 pV/rtHz)
> The preamp has been fixed with a costly :-( wet slug tantalum in the 
> meantime.
> 
> regards,
> Gerhard
> 
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Re: [time-nuts] TNS-BUF update

[Bruce Griffiths]

Yes, I looked at the plots and I see exactly what I described.
2nV/rtHz at frequencies somewhat above the reference current source output RC 
filter, rising to a high value at frequencies below the current source output 
filter pole.
This is an inherent property of the architecture.
The LT3042 is better in this regard than TI's offerings but only because its 
easy to filter the reference and set the filter pole frequency much lower.
Its also quieter than the Abracon low noise supply that I have. 

Bruce 
> On 20 August 2018 at 00:25 Gerhard Hoffmann  wrote:
> 
> 
> You did not take a look at the plots, did you?
> 
> It is seldom to find these data taken all in an identical setup.
> 
> 
> Am 19.08.2018 um 14:07 schrieb Bruce Griffiths:
> > The LT3042 is still inherently very noisy at ultra low frequencies 
> > approaching and below the pole frequency (can be well below 1Hz) of the 
> > reference filter (There's a limit to the maximum capacitance 
> > available/feasible). Forward biased diodes including LEDs are quieter in 
> > this region.
> >
> Gerhard
> 
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Re: [time-nuts] TNS-BUF update

[Bruce Griffiths]

There are some NIR sensitive photodiodes that take advantage of the NIR 
transparency of some black epoxies.
Bruce
> On 20 August 2018 at 02:48 Dana Whitlow  wrote:
> 
> 
> Be watchful about the black epoxy.   It may just be a dyed (otherwise
> clear) epoxy,
> and some of the black dyes in common use pass near IR quite readily.  This
> would
> probably be most troublesome if the ambient light source were of the
> incandescent
> persuasion.
> 
> Also, small diodes in clear packages can also make photodetectors.  I once,
> in
> desperation at a customer's site, successfully kluged a slightly
> sub-nanosecond
> detector out of a 1N914 (or one of those types like that) and a 9V battery.
> 
> Dana
> 
> 
> On Sun, Aug 19, 2018 at 8:15 AM, Didier Juges  wrote:
> 
> > That's a very good point. I have used LEDs as photocells many times, the
> > first time was in 1974 when it was easier for this university student to
> > get LEDs than photocells.
> >
> > I have also made a bi-directional optically isolated data link using a
> > single fiber optic cable and two fiber optic transmitters (LEDs) in the
> > HFBR-500 series.
> >
> > A couple coats of black paint, or a dab of black epoxy covering the LED
> > should work. Include the back side of the PWB for good measure, this is
> > time-nuts :)
> >
> > Didier KO4BB
> >
> >
> > On Sun, Aug 19, 2018, 3:38 AM Poul-Henning Kamp 
> > wrote:
> >
> > > 
> > > In message <1818735266.3837388.1534666949...@webmail.xtra.co.nz>, Bruce
> > > Griffit
> > > hs writes:
> > >
> > > >It exploits the fact that for a RED LED at least the difference
> > > >between the LED forward voltage and the transistor Vbe is ~ 1V and
> > > >has a fairly low tempco and has low noise (at  least for RED LEDs).
> > >
> > > ... in darkness.
> > >
> > > When using LEDs this sort of way, they should always be totally
> > > shielded from all external light.
> > >
> > > --
> > > Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> > > p...@freebsd.org | TCP/IP since RFC 956
> > > FreeBSD committer   | BSD since 4.3-tahoe
> > > Never attribute to malice what can adequately be explained by
> > incompetence.
> > >
> > >
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Re: [time-nuts] TNS-BUF update

[Bruce Griffiths]

Without the benefit of agressive low pass filtering the noise of an LT3042 at 
10Hz is at least an order of magnitude worse than that of an unfiltered LED for 
the same output voltage.
The noise of Nitride passivated LEDs degrades significantly with aging and 
there is a strong correlation between LED noise and its quality / aging 
degradation.  

http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p10.pdf

Bruce
> On 20 August 2018 at 03:42 Gerhard Hoffmann  wrote:
> 
> 
> 
> 
> Am 19.08.2018 um 14:43 schrieb Bruce Griffiths:
> > Yes, I looked at the plots and I see exactly what I described.
> > 2nV/rtHz at frequencies somewhat above the reference current source output 
> > RC filter, rising to a high value at frequencies below the current source 
> > output filter pole.
> > This is an inherent property of the architecture.
> 
> I really don't know how you come to that conclusion. Even the HLMP-6000 
> needs more than
> 100 Hz to be better than the 3042 in its standard data sheet circuit, 
> without extra filtering
> provided, and the LED delivers only half the DC voltage, another 6 dB.
> 
> 'Ordinary' LEDs from Toshiba or Osram(ex Siemens) are 20 to 30 db worse, 
> and they are
> quality parts, not unknown junk box parts.
> Their 1/f corner is - OMG!!!11! -  the plot goes only to 1 MHz!
> 
> Postulating superior LED  performance at 1Hz from that is quite venturesome.
> LEDs are good in comparison to el cheapo bandgaps and high voltage "Zeners",
> but they cannot do magic.
> 
> 
> And please don't say, it's the light. The measurements are made in a box 
> in a box in a box
> to handle the pV noise densities. My preamps are now at 70 pV/rtHz and 
> there is a
> chopper in statu nascendi at 100 pV sub- 0.1 Hz. Yes, I see the noise 
> of  the 0.6 Ohm switches.
> 
> But I need a better FFT analyzer now. A working SPI driver @ 
> 1Mtransfers/sec for the
> BeagleBoneBlack would do.
> 
> cheers, Gerhard
> 
> 
> ps. I'm also interested in that time travel movie.
> 
> 
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Re: [time-nuts] Lars GPSDO on EEVblog

[Bruce Griffiths]

Use the phase detector output to drive the tristate control input of a fast 
CMOS tristate state buffer (eg 74HC126 or faster) which in turn drives the RC 
network eliminating the diode.
Then correct for the exponential charging characteristics using the micro.

For best results increase ADC resolution by 1 bit or more and set RC charge 
time constant to around the maximum expected time interval.
Using a 2 stage synchroniser to drive the tristate control input of the buffer 
to minimise metastability issues may also be useful.

Even linear Time to amplitude converter circuits using a current source exhibit 
nonlinearities. Its easy enough to calibrate the nonlinearity of a simple TAC.

Bruce
 
> On 09 September 2018 at 14:17 Jim Harman  wrote:
> 
> 
> Charles wrote,
> >
> > According to my tests, the B-C junction of a high-quality 2N3904 has
> > about 50pA of leakage at 20vDC reverse voltage.
> 
> 
> That's good to know, but the problem I had with this circuit was with the
> forward current at a low forward voltage. With this phase detector, the
> HC4046 makes a 0 to 1 usec pulse representing the time difference between
> the 1 pps from the GPS and the 1 MHz derived from the OCXO. This charges
> the capacitor to a voltage proportional to the width of the pulse, the ADC
> measures the capacitor voltage, and the cap discharges through the 1 Meg
> resistor during the rest of the second.
> 
> When the HC4046 output goes low at the end of the pulse, the voltage on the
> other side of the 1N5711 diode goes down to about 0.4 V. With a 1N4148 or
> similar diode instead of the transistor, the forward current after the
> capacitor is mostly discharged through the 1 meg resistor is enough to
> prevent the capacitor from discharging all the way and the minimum voltage
> at the ADC is about 0.3 V. or about 120 counts on the ADC. I was able to
> get this below 90 counts by using the transistor. It might be possible to
> reduce the 1 Meg resistor, but then we risk significantly discharging the
> capacitor in the short time between the end of the pulse and the A/D
> reading.
> 
> I would certainly be interested in any suggestions on improving this
> circuit.
> 
> >
> >
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Re: [time-nuts] 10 MHz -> 16 MHz

[Bruce Griffiths]

Full wave rectify the sinewave input, extract the 8th Harmonic with a passive 
filter.
Drive the input of a divide by 5 circuit via a suitable impedance converter 
network.
Could even use a CMOS 74XX74 flipflop plus a few passive components as the 
divider.

Bruce

> On 30 September 2018 at 16:57 Tom Van Baak  wrote:
> 
> 
> What's a clever, simple, reliable (pick 2 of 3) way to get 16 MHz out of 10 
> MHz? Low phase noise isn't a big requirement and jitter doesn't need to be 
> sub-nanosecond. The main requirement is perfect cycle count accuracy. This is 
> for driving a 16 MHz microcontroller from a 10 MHz Rb/Cs/GPSDO. 10 MHz input 
> is likely sine; 16 MHz output is 3v3 or 5v CMOS.
> 
> Thanks,
> /tvb
> 
> 
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Re: [time-nuts] 10 MHz -> 16 MHz

[Bruce Griffiths]

A low phase noise method is to use a dual conjugate regenerative divider with 
6MHz and 16Mhz bandpass filters in the feedback loop to produce 16Mhz output.

For 12MHz output use 2MHz and 12MHz bandpass filters in the feedback loop. 

Bruce
> On 01 October 2018 at 09:05 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> If (as originally specified) noise and jitter are not a big deal - there are 
> a lot 
> of chips out there like the ICS570. They are designed to do weird ratio 
> frequency
> conversions so 10 to 12 or 10 to 16 are trivial for them. The Clockblock 
> board was
> one way to get it all put together. 
> 
> Bob
> 
> > On Sep 30, 2018, at 12:05 PM, Gerhard Hoffmann  wrote:
> > 
> > 
> > Am 30.09.2018 um 16:49 schrieb Attila Kinali:
> > 
> >> The simplest way I can think of is the following:
> >> Use a 74LV8154 to divide the 10MHz down to 152.587890625Hz.
> >> Use the capture timer unit of the uC to measure the phase of the
> >> pulse. Use any kind of DAC (internal, external, PWM,...) to steer
> >> the 16MHz VCO. Depending on how fast the timer unit runs, this
> >> will give you something in the order of 10-200ns dead-band.
> >> By choosing the right frequency for the timer unit, one can
> >> get it to "dither" a bit and then use averaging.
> >> 
> >> For lower jitter, use one half of a Nutt interpolator
> >> to get the timing difference between the 152Hz signal
> >> and the 16MHz (ie similar to what the SRS FS740 does).
> >> Use something akin Nick Sayer's time-to-amplitude converter
> >> for the fine measurement.
> >> 
> >> Same works equally well for 12MHz.
> >> 
> >> 
> > 
> > Wow. That's truly a Rube Goldberg design.
> > 
> > There is a simpler way.  IDT ICS570. Digikey 800-1073-5-ND
> > 
> > Solder time less than 10 minutes.
> > I had the 3V3-Version in the parts drawers, officially it takes the 5V
> > version to generate the 160 MHz, but the 3V3 version happened to work, too.
> > The difference between 120 and 160 MHz is just a GND wire on pin 6 (vs. 
> > open)
> > 
> > Divide by 10 is left as an exercise.
> > 
> > regards,
> > Gerhard
> > 
> > (But then, some like to build and tune multiplier chains and mixers.)
> > 
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Re: [time-nuts] 10 MHz -> 16 MHz

[Bruce Griffiths]

Brian
There are 2 parallel feedback paths one tuned to 6MHz and the other tuned to 
16MHz.
They can either share the same amp or use separate amplifiers. There's a NIST 
paper on using them to divide by factors other than 2 (e.g. 3, 5 etc).
https://tf.nist.gov/general/pdf/1890.pdf

Bruce
> On 04 October 2018 at 00:54 "Brian, WA1ZMS"  wrote:
> 
> 
> Bruce-
> 
> Does such a dual conjugate regen divider use a single mixer with the BPFs in 
> parallel?   Or are there multiple loops?  I'm trying to visualize the 
> topology.
> 
> I've built a few divide-by-2 regen dividers (both worked very well) but 
> nothing else.
> 
> -Brian
> 
> 
> > On Sep 30, 2018, at 4:25 PM, Bruce Griffiths  
> > wrote:
> > 
> > A low phase noise method is to use a dual conjugate regenerative divider 
> > with 6MHz and 16Mhz bandpass filters in the feedback loop to produce 16Mhz 
> > output.
> > 
> > For 12MHz output use 2MHz and 12MHz bandpass filters in the feedback loop. 
> > 
> > Bruce
> >> On 01 October 2018 at 09:05 Bob kb8tq  wrote:
> >> 
> >> 
> >> Hi
> >> 
> >> If (as originally specified) noise and jitter are not a big deal - there 
> >> are a lot 
> >> of chips out there like the ICS570. They are designed to do weird ratio 
> >> frequency
> >> conversions so 10 to 12 or 10 to 16 are trivial for them. The Clockblock 
> >> board was
> >> one way to get it all put together. 
> >> 
> >> Bob
> >> 
> >>> On Sep 30, 2018, at 12:05 PM, Gerhard Hoffmann  wrote:
> >>> 
> >>> 
> >>>> Am 30.09.2018 um 16:49 schrieb Attila Kinali:
> >>>> 
> >>>> The simplest way I can think of is the following:
> >>>> Use a 74LV8154 to divide the 10MHz down to 152.587890625Hz.
> >>>> Use the capture timer unit of the uC to measure the phase of the
> >>>> pulse. Use any kind of DAC (internal, external, PWM,...) to steer
> >>>> the 16MHz VCO. Depending on how fast the timer unit runs, this
> >>>> will give you something in the order of 10-200ns dead-band.
> >>>> By choosing the right frequency for the timer unit, one can
> >>>> get it to "dither" a bit and then use averaging.
> >>>> 
> >>>> For lower jitter, use one half of a Nutt interpolator
> >>>> to get the timing difference between the 152Hz signal
> >>>> and the 16MHz (ie similar to what the SRS FS740 does).
> >>>> Use something akin Nick Sayer's time-to-amplitude converter
> >>>> for the fine measurement.
> >>>> 
> >>>> Same works equally well for 12MHz.
> >>>> 
> >>>> 
> 
> 
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Re: [time-nuts] NIST Time and Frequency Publication Database

[Bruce Griffiths]

Leaving all entries on the search form blank returns a list of all their t&f 
publications in the database. 

Bruce

> On 04 October 2018 at 09:55 Magnus Danielson  
> wrote:
> 
> 
> Fellow time-nuts,
> 
> I just wanted to remind you about the wonderful resource that the NIST
> Time and Frequency Publication Database is. It's a good way to find lots
> of good articles.
> 
> https://tf.nist.gov/general/publications.htm
> 
> Once you find an article, search on the writes names to find more good
> stuff.
> 
> Today was the day when I accidentally found an article that I co-wrote.
> Somewhat proud of that.
> 
> Interesting writers to search for is Allan, Weiss, Barnes, Howe, Walls,
> Nelson, Hati, Gray and Stein should get you started.
> 
> "regenerative" is a good search there for regenerative dividers for
> instance.
> 
> David Howe has written "Interpreting Oscillatory Frequency Stability
> Plots" for instance, which may be of some interest for some here:
> https://tf.nist.gov/general/pdf/1808.pdf
> I just found it. Happy to find fellow Bill Riley, Francois Vernotte and
> Charles Greenhall in the acknowledgement section.
> 
> Cheers,
> Magnus
> 
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Re: [time-nuts] Minicircuits SYPD-1

[Bruce Griffiths]

NIST used off the shelf RF transformers in their mixers based  on diode 
connected (collector connected directly to base) 2N. The transformer 
impedance ratios (!:5 IIRC) are specified in the papers on the mixer 
performance. 
Suitable transformers are made by Minicircuits and others.

Bruce

> On 20 December 2018 at 07:04 Jerry Hancock  wrote:
> 
> 
> Thanks to all that replied, lots of good info which will take me months to 
> sort through, especially the link to Jürg Kögel looks helpful as well as a 
> note from Bert.
> 
> Attila, Yes, more phase noise than long term though this is really an 
> exercise to get a better understanding of oscillators and measurement 
> techniques.
> 
> The 2n mixer sounds like another H-mode, I’ll have to look at it.  It 
> probably uses self-wound, micro-sized bobbins which will be a challenge for 
> me :-].
> 
> Bob, I think you were the person who pointed me to the loose PLL a while 
> back.  The circuit I am building used a gain of 300ish (30k/100) and I expect 
> that to really clip when unlocked.  I have a 10-turn variable in the circuit 
> to bring it close initially. 
> 
> Another question or if you can point me to the method, if you are using 
> quadrature signals, is the measurement then the geometric sum? Or do you mix 
> them back together?  I am using a 3457a on the PD after an amp right now and 
> I would think you would need either another meter, which I have, or a 
> scanner, again I have both.  
> 
> My N2PK VNA uses two 24bit, low noise ADCs (LTC2410) for the same purpose 
> more or less. It has effectively two DC receivers with two DDS. I can throw 
> away the DDS and mixers and just read the DC voltage.  I have a second N2PK 
> board I never finished as I planned to use another master oscillator on it 
> with lower PN, but I needed a couple of parts and my tremor made SMD 
> soldering difficult.  This was one of the drivers for my interest in phase 
> noise. Now that I think about it, I can repurpose the second board, bypassing 
> the MC1496 mixers. They are filtered to be close to DC within a few hz and 
> has -135dB noise floor.  I can even change the input filter to use the 220 
> ohm/.0046uf R/C recommended.
> 
> I wish there was a way to use or modify one of my 8568B Spectrum analyzers to 
> do this.
> 
> Regards,
> 
> Jerry
> 
> 
> > On Dec 19, 2018, at 7:57 AM, Attila Kinali  wrote:
> > 
> > Hoi Jerry,
> > 
> > On Tue, 18 Dec 2018 23:18:42 -0800
> > jerry  wrote:
> > 
> >> I'm playing around with various methods of collecting data for
> >> oscillator testing and would like to try the loose PLL which
> >> requires a phase detector (PD).  
> > 
> > I guess you are looking more into phase noise than stability?
> > 
> >> I'm testing an AD8302 but that has a flat spot around 176 to 180 degrees.
> > 
> > All phase detectors exhibit non-linearity in some form or other.
> > If you get all the way to +/-176° with good linearity, then be
> > happy. If you need more than that, then you have to either use
> > two phase detectors that are driven with a reference that is 90°
> > apart, or you have to digitize the signal and do the same in digital.
> > 
> >>  One of the papers I read recommended the subject PD but it is out of
> >> stock everywhere, including the subs. One Minicircuits PD is in stock but
> >> pricey.  I can try a double balanced mixer like the SBL or TUF series 
> >> (which
> >> I have on hand) but I thought maybe someone on the list has the subject PD
> >> they dont need. If so, please send me a note.
> > 
> > There is a decent alternative: Use two transformers and 4 2N to
> > do your own mixer. The quality of it, according to NIST[1] is pretty
> > good. I assume that any other NPN transistor of similar make-up will
> > also do and lead to same/similar performance.
> > 
> > You might also want to have a look at Enrico's Mixer Tutorial[2]
> > 
> >> I'm slowly gathering parts for Riley's small Dual Mixer Time Difference
> >> test kit but it will take some time which I'm unfortunately running out
> >> of due to mild Parkinsons getting in the way of SMD soldering. I've used
> >> my HP 5371a in the past but it sounds like a jet engine.  I recently
> >> ordered a TICC as well.  By the time I'm done I probably will have
> >> purchased more than a commercial  product, ha!
> > 
> > Jürg Kögel did a redesign of the Riley DMTD earlier this year,
> > which looks very nice. And the measurements I've seen are very
> > impressive (it's on par with the best state of the art I am aware of).
> > So you might want to contact him and see whether he has some board left.
> > 
> > Attila Kinali
> > 
> > 
> > [1] "Residual PM Noise Evaluation of Radio Frequecny Mixers"
> > by Barnes, Hati, Nelson, Howe, 2011
> > https://doi.org/10.1109/FCS.2011.5977868
> > http://time.kinali.ch/mixers/residual_pm_noise_evaluation_of_radio_frequency_mixers-2011-barnes_hati_nelson_howe-05977868.pdf
> > 
> > [2] "Tutorial on the double-balanced mixer"
> >

Re: [time-nuts] HP Stories: Frequency Counter business decline, Modulation Domain Analyzers, geeks as models

[Bruce Griffiths]

https://www.arl.wustl.edu/~jst/cse/260/glitchChaney.pdf
suggests metastability was noticed in the 1940's but not taken seriously for 
decades thereafter.

Bruce
> On 21 January 2019 at 19:10 Hal Murray  wrote:
> 
> 
> 
> When did people designing counter/timers start paying attention to 
> metastability?
> 
> I learned about it in the late 70s or early 80s.  In the mid 80s, I went to a 
> trade show that had a panel on it, and one of the panelists actually claimed 
> it wasn't a problem.
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] HP Stories: Battery Chargers, and a fading idolization of HP

[Bruce Griffiths]

Mica is a sheet silicate mineral little or no carbon present.
Bruce
> On 11 February 2019 at 11:15 Bob Bownes  wrote:
> 
> 
> > 
> > Yes, those brown roughly 1" square caps used intact sheets of mica as 
> > dielectric. You can easily split the mineral into uniform, thin, 
> > transparent sheets.
> 
> Beware inclusions that will make the surface rough and change the behavior, 
> particularly breakdown voltages. 
> 
> > The reconstituted caps are still around - used in high power RF circuits 
> > (mica has really low loss, but high epsilon) and in Tesla coils (a sort of 
> > special case high power RF). Most of them are surplus Russian/Soviet.
> > 
> Hmm, mica is pretty much hexagonal version of graphite/carbon/diamond created 
> when there is a large axial force and the proper temperature. It is 
> synthesized for many uses today, I’d be very surprised if precision high 
> voltage caps was not one of them. 
> 
> That being said, thanks for the insights into the 5061A/B. Now I feel the 
> need to go power mine up!
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Re: [time-nuts] GN-GGB0710 GPS Antenna Mounting Thread

[Bruce Griffiths]

NPT or BSPT pipe thread perhaps?

Bruce

> On 15 February 2019 at 14:08 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> Indeed for an antenna that is going on a mount one time and one time only a 
> “tapered” thread
> might make sense. Crank it down and it locks in place …..
> 
> Bob
> 
> > On Feb 14, 2019, at 5:34 PM, Hal Murray  wrote:
> > 
> >> I’ve had no issues with 5/8-11 going into any of the Chinese antennas so 
> >> far.  
> > 
> > I have at least one antenna with threads that seem right but don't go in 
> > more 
> > than a few turns.  I'll try to find it if people want more data.
> > 
> > 
> > -- 
> > These are my opinions.  I hate spam.
> > 
> > 
> > 
> > 
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Re: [time-nuts] GN-GGB0710 GPS Antenna Mounting Thread

[Bruce Griffiths]

3/8" (nominal bore) NPT thread has an outer diameter near 5/8" and has 18 
threads/inch somewhat finer than the 5/8 11 TPI used for most surveying antennae

Bruce

> On 23 February 2019 at 11:06 David Witten  wrote:
> 
> 
> FWIW
> 
> I just poked around my shop and found something that fit perfectly.  It was
> a 5/8 inch plumbing 'barb'.  So I just went to to a big-box  hardware store
> (Lowes) and went to the plumbing section.  The sales person agreed with me
> that it seemed to be tapered and I found a nice 8 inch length of brass
> extension threaded on both ends.  It fit snugly and seems well suited for
> attachment to a larger pole using a couple of hose clamps.
> 
> Dave Witten
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Re: [time-nuts] Smaller, and smaller antennas

[Bruce Griffiths]

2.4/0.1 = 24 not 240 !!!

Bruce
> On 06 March 2019 at 17:36 jimlux  wrote:
> 
> 
> On 3/5/19 3:05 PM, Charles Steinmetz wrote:
> > Ho, hum, yet another fantastical claim for magical gain from a 
> > tiny-for-wavelength antenna.
> > 
> > See the many discussions of same by Kurt N. Sterba over the last several 
> > decades, among many, many others.
> > 
> > The laws of physics are stubborn things
> 
> 
> these don't violate the theoretical limits.. 100 MHz BW at 2.4 GHz is 
> pretty high Q (240).
> 
> What I'm interested in is the internal construction -  lambda at 2.4 GHz 
> is 122 mm, and these things are 3x3x4mm.  If you tried to dielectrically 
> load a half wavelength from 61 down to 3mm, that's a factor of 20, which 
> implies an epsilon of 400.  Clearly, that's not what they're doing.
> 
> I'm a bit suspicious about that long feedline in the test fixture.
> 
> 
> Johansen has lots of these in various frequencies and sizes
> https://www.johansontechnology.com/antennas
> 
> Tons of WiFi (2.45 GHz) antennas in all sizes and shapes.
> 
> GPS/GLONASS antennas too
> https://www.johansontechnology.com/datasheets/1575AT54A0010/1575AT54A0010.pdf
> 12x4mm
> 
> 
> 
> 
> > 
> > Best regards,
> > 
> > Charles
> > 
> > 
> > On 3/5/2019 1:48 PM, jimlux wrote:
> >> On 3/5/19 9:33 AM, Gregory Beat via time-nuts wrote:
> >>> No, this is not an “L-band”, GNSS antenna ... BUT it demonstrates the
> >>> shrinking size.
> >>>
> >>> NEW Molex 206513 Antenna for 2.4 GHz, 3x3x4 mm in size.
> >>> Less than $1.00 for quantity 1, both Mouser and Digi-Key now stocking.
> >>> https://www.digikey.com/en/product-highlight/m/molex/2-4-ghz-ceramic-antenna
> >>>  
> >>>
> >>>
> >>>
> >>> Molex’s 206513 series is a 2.4 GHz embedded ceramic antenna with high
> >>> efficiency over 55% on all frequency bands. This miniature SMT ceramic
> >>> component requires a very small (4 mm x 4 mm) keep-out area and is
> >>> designed to be mounted directly at the corner of the main device PCB.
> >>> It has a frequency range of 2.4 GHz - 2.5 GHz, return loss of <-6 dB,
> >>> and peak gain (max) 3.6 dBi. It features an omnidirectional radiation
> >>> pattern.
> >>>
> >>
> >> One needs to carefully look at the 55% claim with these kinds of things.
> >>   Are they including that in the gain, 50% efficiency is a gain hit of
> >> 3dB? Peak gain of 3.6dBi (is that circular or linear?) (is that
> >> directivity, or gain?). Does the efficiency count the 25% of the power
> >> reflected back from the 6dB return loss?
> >>
> >> https://www.molex.com/pdm_docs/ps/2065130001-PS.pdf is more about 
> >> packaging
> >>
> >> https://www.molex.com/pdm_docs/as/2065130001-AS.pdf has the antenna
> >> patterns..
> >>
> >>
> >>
> >> Also, what's the axial ratio off boresight...
> >>
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Re: [time-nuts] Absolute time accuracy pre-Cesium?

[Bruce Griffiths]

John
http://adsabs.harvard.edu/full/1968JRASC..62..205T
indicates a timing accuracy of a few milliseconds was typical for the Calgary 
PZT.

Bruce
> On 26 March 2019 at 11:44 John Ackermann N8UR  wrote:
> 
> 
> Does anyone have a pointer to information about the absolute time 
> accuracy (not stability) that was available via PZT or other techniques 
> prior to the Cesium definition?  I'm doing a presentation and want to 
> show the evolution of accuracy.  My Google-fu has failed me in finding 
> anything pre-Atomic.
> 
> Thanks!
> John
> 
> 
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Re: [time-nuts] Absolute time accuracy pre-Cesium?

[Bruce Griffiths]

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/FFA10ED6A784AA1E39637CC0CA93B750/S0074180900036007a.pdf/div-class-title-some-advantages-and-disadvantages-of-a-photographic-zenith-tube-div.pdf
indicates a timing error of around 6 millisec

Bruce
> On 26 March 2019 at 12:15 Bruce Griffiths  wrote:
> 
> 
> John
> http://adsabs.harvard.edu/full/1968JRASC..62..205T
> indicates a timing accuracy of a few milliseconds was typical for the Calgary 
> PZT.
> 
> Bruce
> > On 26 March 2019 at 11:44 John Ackermann N8UR  wrote:
> > 
> > 
> > Does anyone have a pointer to information about the absolute time 
> > accuracy (not stability) that was available via PZT or other techniques 
> > prior to the Cesium definition?  I'm doing a presentation and want to 
> > show the evolution of accuracy.  My Google-fu has failed me in finding 
> > anything pre-Atomic.
> > 
> > Thanks!
> > John
> > 
> > 
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Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest

[Bruce Griffiths]

The Danjon impersonal astrolabe is perhaps better suited to accurate 
measurements:
https://www.nzmuseums.co.nz/collections/3267/objects/3380/astrolabe

Bruce
> On 27 March 2019 at 15:48 Tom Van Baak  wrote:
> 
> 
> BobH wrote:
> >> This would be an excellent project for time-nuts to verify.  First, a
> >> better explanation of John Harrison’s method is in order.  A vertical
> >> window edge is not sufficient - a second vertical reference at a
> >> distance is required - Harrison used a chimney on a neighbor's house.
> 
> Agreed! The project is the perfect intersection of amateur astronomy and 
> amateur timekeeping. Surely, a couple of people on the list could 1) attempt 
> to verify the Harrison method, and 2) determine what the limits of its 
> accuracy are, say, with little effort vs. with hard work vs. with extreme 
> dedication.
> 
> JimL wrote:
> > To get 1 second accuracy, you need 360/86400 = 0.004 degree 
> > measurements. That's 0.073 milliradian - 1 cm  at 140 meter distance.
> > 
> > I'm not sure an "edge" is sharp enough (diffraction, etc.), although 
> > your eye is pretty good at "deconvolving" the linear equivalent of an 
> > Airy disk/rings.
> 
> Keep in mind too that one can take more than one star reading per night. Any 
> identifiable star that crosses your edge is a recordable timing event that 
> evening. So, in theory, if you measure N stars you get sqrt(N) improvement in 
> accuracy per day.
> 
> I want to encourage anyone to study the problem and help solve the riddle, 
> either by uncovering existing professional or amateur literature or by 
> actually trying this at home. It boils down to how accurately can you measure 
> earth rotation using the Harrison method.
> 
> To put this in time nuts context, precision timekeeping prior to the middle 
> of the 20th century was always a form of "Earth Disciplined Oscillator". Not 
> unlike a GPSDO, your observatory's pendulum clock kept accurate time 
> short-term and star tracking (earth rotation) kept accurate time long-term. 
> The ADEV's crossed just like a GPSDO.
> 
> The short-term ADEV of a really good pendulum clock is here:
> 
> http://leapsecond.com/pend/shortt/
> 
> The long-term ADEV of earth rotation is here:
> 
> http://leapsecond.com/museum/earth/
> 
> So the performance of a DIY earth disciplined oscillator would be a 
> combination of the two.
> 
> /tvb
> 
> 
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Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest

[Bruce Griffiths]

These light curves for a star being occulted by the moon should give some idea 
of the effects of diffraction:

http://tdc-www.harvard.edu/occultations/moon/vb141occa.html

Bruce 
> On 27 March 2019 at 15:48 Tom Van Baak  wrote:
> 
> 
> BobH wrote:
> >> This would be an excellent project for time-nuts to verify.  First, a
> >> better explanation of John Harrison’s method is in order.  A vertical
> >> window edge is not sufficient - a second vertical reference at a
> >> distance is required - Harrison used a chimney on a neighbor's house.
> 
> Agreed! The project is the perfect intersection of amateur astronomy and 
> amateur timekeeping. Surely, a couple of people on the list could 1) attempt 
> to verify the Harrison method, and 2) determine what the limits of its 
> accuracy are, say, with little effort vs. with hard work vs. with extreme 
> dedication.
> 
> JimL wrote:
> > To get 1 second accuracy, you need 360/86400 = 0.004 degree 
> > measurements. That's 0.073 milliradian - 1 cm  at 140 meter distance.
> > 
> > I'm not sure an "edge" is sharp enough (diffraction, etc.), although 
> > your eye is pretty good at "deconvolving" the linear equivalent of an 
> > Airy disk/rings.
> 
> Keep in mind too that one can take more than one star reading per night. Any 
> identifiable star that crosses your edge is a recordable timing event that 
> evening. So, in theory, if you measure N stars you get sqrt(N) improvement in 
> accuracy per day.
> 
> I want to encourage anyone to study the problem and help solve the riddle, 
> either by uncovering existing professional or amateur literature or by 
> actually trying this at home. It boils down to how accurately can you measure 
> earth rotation using the Harrison method.
> 
> To put this in time nuts context, precision timekeeping prior to the middle 
> of the 20th century was always a form of "Earth Disciplined Oscillator". Not 
> unlike a GPSDO, your observatory's pendulum clock kept accurate time 
> short-term and star tracking (earth rotation) kept accurate time long-term. 
> The ADEV's crossed just like a GPSDO.
> 
> The short-term ADEV of a really good pendulum clock is here:
> 
> http://leapsecond.com/pend/shortt/
> 
> The long-term ADEV of earth rotation is here:
> 
> http://leapsecond.com/museum/earth/
> 
> So the performance of a DIY earth disciplined oscillator would be a 
> combination of the two.
> 
> /tvb
> 
> 
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Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest

[Bruce Griffiths]

Of course the time scale will be much shorter for a star occulted by an edge 
etc on Earth.
The longer time scale for a lunar occultation is due to the slower relative 
angular motion of the moon with respect to the star than the motion of the 
Earth with respect to a star.
 
Bruce 
> On 27 March 2019 at 17:41 Bruce Griffiths  wrote:
> 
> 
> These light curves for a star being occulted by the moon should give some 
> idea of the effects of diffraction:
> 
> http://tdc-www.harvard.edu/occultations/moon/vb141occa.html
> 
> Bruce 
> > On 27 March 2019 at 15:48 Tom Van Baak  wrote:
> > 
> > 
> > BobH wrote:
> > >> This would be an excellent project for time-nuts to verify.  First, a
> > >> better explanation of John Harrison’s method is in order.  A vertical
> > >> window edge is not sufficient - a second vertical reference at a
> > >> distance is required - Harrison used a chimney on a neighbor's house.
> > 
> > Agreed! The project is the perfect intersection of amateur astronomy and 
> > amateur timekeeping. Surely, a couple of people on the list could 1) 
> > attempt to verify the Harrison method, and 2) determine what the limits of 
> > its accuracy are, say, with little effort vs. with hard work vs. with 
> > extreme dedication.
> > 
> > JimL wrote:
> > > To get 1 second accuracy, you need 360/86400 = 0.004 degree 
> > > measurements. That's 0.073 milliradian - 1 cm  at 140 meter distance.
> > > 
> > > I'm not sure an "edge" is sharp enough (diffraction, etc.), although 
> > > your eye is pretty good at "deconvolving" the linear equivalent of an 
> > > Airy disk/rings.
> > 
> > Keep in mind too that one can take more than one star reading per night. 
> > Any identifiable star that crosses your edge is a recordable timing event 
> > that evening. So, in theory, if you measure N stars you get sqrt(N) 
> > improvement in accuracy per day.
> > 
> > I want to encourage anyone to study the problem and help solve the riddle, 
> > either by uncovering existing professional or amateur literature or by 
> > actually trying this at home. It boils down to how accurately can you 
> > measure earth rotation using the Harrison method.
> > 
> > To put this in time nuts context, precision timekeeping prior to the middle 
> > of the 20th century was always a form of "Earth Disciplined Oscillator". 
> > Not unlike a GPSDO, your observatory's pendulum clock kept accurate time 
> > short-term and star tracking (earth rotation) kept accurate time long-term. 
> > The ADEV's crossed just like a GPSDO.
> > 
> > The short-term ADEV of a really good pendulum clock is here:
> > 
> > http://leapsecond.com/pend/shortt/
> > 
> > The long-term ADEV of earth rotation is here:
> > 
> > http://leapsecond.com/museum/earth/
> > 
> > So the performance of a DIY earth disciplined oscillator would be a 
> > combination of the two.
> > 
> > /tvb
> > 
> > 
> > ___
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> > To unsubscribe, go to 
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> 
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Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest

[Bruce Griffiths]

Brooke

Yes but the accuracy would suffer due to observer related effects.
However when used with a CCD camera or equivalent the accuracy should improve 
somewhat much as adding a TV camera to a transit circle improved its accuracy. 
I had a personal tour of the USNO setup on Black- Birch/Altimarloch during 
their southern hemisphere campaign during the 1980's. 

Bruce
> On 27 March 2019 at 20:39 Brooke Clarke  wrote:
> 
> 
> Hi Bruce:
> 
> Would the David White 60 Degree Pendulum Astrolabe also work?
> https://prc68.com/I/PendulumAstrolabe.shtml
> 
> -- 
> Have Fun,
> 
> Brooke Clarke
> https://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
> axioms:
> 1. The extent to which you can fix or improve something will be limited by 
> how well you understand how it works.
> 2. Everybody, with no exceptions, holds false beliefs.
> 
>  Original Message 
> > The Danjon impersonal astrolabe is perhaps better suited to accurate 
> > measurements:
> > https://www.nzmuseums.co.nz/collections/3267/objects/3380/astrolabe
> >
> > Bruce
> >> On 27 March 2019 at 15:48 Tom Van Baak  wrote:
> >>
> >>
> >> BobH wrote:
>  This would be an excellent project for time-nuts to verify.  First, a
>  better explanation of John Harrison’s method is in order.  A vertical
>  window edge is not sufficient - a second vertical reference at a
>  distance is required - Harrison used a chimney on a neighbor's house.
> >> Agreed! The project is the perfect intersection of amateur astronomy and 
> >> amateur timekeeping. Surely, a couple of people on the list could 1) 
> >> attempt to verify the Harrison method, and 2) determine what the limits of 
> >> its accuracy are, say, with little effort vs. with hard work vs. with 
> >> extreme dedication.
> >>
> >> JimL wrote:
> >>> To get 1 second accuracy, you need 360/86400 = 0.004 degree
> >>> measurements. That's 0.073 milliradian - 1 cm  at 140 meter distance.
> >>>
> >>> I'm not sure an "edge" is sharp enough (diffraction, etc.), although
> >>> your eye is pretty good at "deconvolving" the linear equivalent of an
> >>> Airy disk/rings.
> >> Keep in mind too that one can take more than one star reading per night. 
> >> Any identifiable star that crosses your edge is a recordable timing event 
> >> that evening. So, in theory, if you measure N stars you get sqrt(N) 
> >> improvement in accuracy per day.
> >>
> >> I want to encourage anyone to study the problem and help solve the riddle, 
> >> either by uncovering existing professional or amateur literature or by 
> >> actually trying this at home. It boils down to how accurately can you 
> >> measure earth rotation using the Harrison method.
> >>
> >> To put this in time nuts context, precision timekeeping prior to the 
> >> middle of the 20th century was always a form of "Earth Disciplined 
> >> Oscillator". Not unlike a GPSDO, your observatory's pendulum clock kept 
> >> accurate time short-term and star tracking (earth rotation) kept accurate 
> >> time long-term. The ADEV's crossed just like a GPSDO.
> >>
> >> The short-term ADEV of a really good pendulum clock is here:
> >>
> >> http://leapsecond.com/pend/shortt/
> >>
> >> The long-term ADEV of earth rotation is here:
> >>
> >> http://leapsecond.com/museum/earth/
> >>
> >> So the performance of a DIY earth disciplined oscillator would be a 
> >> combination of the two.
> >>
> >> /tvb
> >>
> >>
> >> ___
> >> 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.
> > ___
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> > and follow the instructions there.
> >
> >
>

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Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest

[Bruce Griffiths]

In principle one could time tag each individual photon with subnanosecond 
resolution.

Bruce
> On 29 March 2019 at 09:00 Poul-Henning Kamp  wrote:
> 
> 
> 
> In message <236772484.9174006.1553757616...@webmail.xtra.co.nz>, Bruce 
> Griffith
> s writes:
> 
> >However when used with a CCD camera or equivalent the accuracy
> >should improve somewhat much as adding a TV camera to a transit
> >circle improved its accuracy.
> 
> You know ... there *is* an official time-nut way to do this.
> 
> You want is a chevron shaped 'Høg grid' because that is
> objectively a very, very, very smart way of converting precise
> time to precise geometry.
> 
> I don't know of any popular explanations, but look at page 10 here:
> 
>   https://www.hs.uni-hamburg.de/DE/Ins/Bib/AG2012AK1.pdf
> 
> The illustration on page 10 shows the original concept (from 1925!):
> 
> By modulating the starlight with a non-uniform pattern, and sampling
> the modulated light at high rate, the transit time of the star can
> be determined on the order of the sampling frequency.
> 
> Notice that the photon detector does not need high geometric resolution,
> I belive Strømberg, 17 year old at the time, used a simple photo-cell
> or possibly a photo-multiplier.
> 
> Now, if you want to measure both coordinates, you move to the chevron
> shaped grid illustrated on page 11, the "Høg grid".
> 
> You still get a precise measurement of the transit along the logitudal
> axis, but the width of the signal now also tells you where the star
> was on the transverse axis.
> 
> This is how the Perth 1970 catalog was made, and if not for a loose
> bolt, it would have been the most precise catalog on both axis instead
> of just one axis.
> 
> The Høg grid still leaves rotation as source of error, so look at
> page 2 here:
> 
>   
> https://pdfs.semanticscholar.org/27f4/16df19441874fcd3b1bf52c477c889ca8045.pdf
> 
> Imagine the light-curve you get when a star transits that slit system
> in various directions, including, crucially, with a rotation[1].
> 
> About 12 years ago I did some ad-hoc experiements on my 5" telescope,
> with various simple slit geometries, and it works a treat.
> 
> I made the slits by taping mylar tape on a neutral filter, and cut
> slits with a scalpel and a steel ruler, the detector was a large
> area PIN photo-diode from the junk box and a digital oscilloscope.
> 
> While you can prove the concept, as I did, with portable tripod
> mount, to get usable data you have to bolt the telecope to a cubic
> meter of concrete or bedrock.
> 
> Poul-Henning
> 
> [1] This becaue very important for the Hipparcos satelite which a
> rocket failure left stranded in the parking orbit ... but they still
> completed their science objectives.
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] Neat looking DMTD unit on eBay

[Bruce Griffiths]

The mention of deglitching after the mixers perhaps indicates that the mixers 
may be flipflops and that the device is perhaps a DDMTD. Alternatively the 
block diagram is intentionally misleading.

Bruce 
> On 23 April 2019 at 03:11 cdel...@juno.com wrote:
> 
> 
> Hi,  
> 
> A friend directed me to this listing. Nice looking DMTD unit.
> Low power and compact!
> Has anyone played with one of these yet?
> 
> https://www.ebay.ca/itm/123728915157?ul_noapp=true
> 
> Cheers,
> 
> Corby
> 
> 
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Re: [time-nuts] Query about NRL Canvas source?

[Bruce Griffiths]

CANVAS is apparently northern hemisphere specific.
I just asked and was allowed to download CANVAS including source code

Bruce
> On 28 April 2019 at 01:21 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> Just to confirm - it seems to be broken from here as well.
> 
> Bob
> 
> > On Apr 27, 2019, at 7:31 AM, AC0XU (Jim)  wrote:
> > 
> > Does anyone know how to obtain the NRL Canvas (clock analsis) software?  
> > The widely published link
> > 
> > https://goby.nrl.navy.mil/canvas/
> > 
> > appears to be broken. Thanks!
> > 
> > 
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> 
> 
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Re: [time-nuts] Rubidium Cells for Sale ?!

[Bruce Griffiths]

I asked the seller which cell. We'll see what the response is.
If its filled with RB87 and buffer gas it may be usable with a suitably tuned 
ECDL locked to the correct line.
Bruce
> On 06 May 2019 at 14:04 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> I’m sure they are good cells. The gotcha is “which one is it?”. A normal Rb 
> has multiple 
> cells doing different things. You … umm… errr … need a set of cells ….
> 
> Bob
> 
> > On May 5, 2019, at 5:32 PM, ed_pal...@sasktel.net wrote:
> > 
> > I've seen lots of weird stuff on ebay, but I never thought I'd see this!
> > 
> > https://www.ebay.com/itm/123737315177
> > 
> > Anybody feeling lucky (or desperate!)?
> > 
> > I have no connection with the seller.
> > 
> > Ed
> > 
> > 
> > ___
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> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> 
> 
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Re: [time-nuts] Rubidium Cells for Sale ?!

[Bruce Griffiths]

As expected the seller doesn't know, but offered 2 cells for the price of one 
if further info on the cells he's offering can be provided.
Determining the cell filling would likely be somewhat interesting/challenging.
Absorption spectroscopy using a tunable ECDL comes to mind to sort out the 
Rubidium isotopes present.

Bruce
> On 07 May 2019 at 08:42 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> Ummm ….. e ….. the Efratom Rb’s use an integrated lamp plus one cell. 
> 
> http://www.wriley.com/A%20Modern%20MIL%20Rubidium%20Frequency%20Standard.pdf 
> 
> 
> There still are a lot of people doing the lamp plus two approach. One of many:
> 
> http://www.excelitas.com/Downloads/DTS_Frequency_Standards_RAFS.pdf 
> 
> 
> Bob
> 
> > On May 6, 2019, at 3:23 PM, Ed Palmer  wrote:
> > 
> > 
> > 
> > On 2019-05-06 10:00 AM,  Bob kb8tq wrote:
> >> Hi
> >> 
> >> I?m sure they are good cells. The gotcha is ?which one is it??. A normal 
> >> Rb has multiple
> >> cells doing different things. You ? umm? errr ? need a set of cells ?.
> > 
> > Why do you think I posed the question "Anybody feeling lucky (or 
> > desperate!)?"?  Don't forget that all(?) newer Rb standards use an 
> > integrated cell so it's a 'set' of one.  Whether that's the case here is 
> > unknown, but not likely given the size of this cell.
> > 
> > The only Russian Rb company I've heard of is Kvarz.  Has anyone seen a cell 
> > from one of their old units?
> > 
> > Ed
> > 
> > 
> > ___
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> 
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Re: [time-nuts] generalization of three cornered hat

[Bruce Griffiths]

Try:
https://www.researchgate.net/publication/235103340_Estimating_Frequency_Stability_and_Cross-Correlations

Bruce
> On 16 June 2019 at 10:54 jimlux  wrote:
> 
> 
> I found a lot of references to estimating the uncertainties in 
> measurements derived with three cornered hat.   What about for arbitrary 
> N sources and N(N-1)/2 pair-wise measurements?  There must be some magic 
> term to search for.
> 
> 
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Re: [time-nuts] Using the LT3042

[Bruce Griffiths]

Like virtually all low dropout regulator ICs the LT3042 is quite noisy at 
frequencies below its reference low pass filter high frequency cutoff. Some 
zener based references are considerably quieter in this region.

Bruce
  
> On 10 July 2019 at 18:18 Perry Sandeen via time-nuts 
>  wrote:
> 
> 
> Yo Bubba Dudes!,
> The LT3042 seems to be a wonderful part.  But having learned a long time ago 
> the it wasn't wise to gold plate a Yugo, so when are there diminishing 
> returns?
> For example I have several HP 10811 oscillators. one is in a HP5335a counter 
> that I'd like to make as stable as reasonably possible. Another HP10811 needs 
> a power supply.   Also several Lucent XO OCXO's.
> So where is it practical to hack for better results and when do you use some 
> not -as -wonderful regulator chips that come in a much easier to use dip 
> package for a power supply upgrade?
> Regards,
> Perrier
> 
> 
> 
> 
> 
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Re: [time-nuts] Using the LT3042

[Bruce Griffiths]

Those measurements don't go low enough in frequency to capture the very low 
frequency noise of the LT3042 which uses a noisy current source to produce a 
voltage drop in a resistor as the reference. At low enough frequencies the 
LT3042 is very noisy.  Low pass reference filters with milliHz or lower cutoff 
frequencies are usually impractical. 

Bruce
> On 10 July 2019 at 22:58 Gerhard Hoffmann  wrote:
> 
> 
> 
> Am 10.07.19 um 11:27 schrieb Bruce Griffiths:
> > Like virtually all low dropout regulator ICs the LT3042 is quite noisy at 
> > frequencies below its reference low pass filter high frequency cutoff. Some 
> > zener based references are considerably quieter in this region.
> 
> We had that already last year.
> 
> I have delivered measured curves that show that it's not true.
> 
> The trick of the LT3042 is that it's reference is not very noisy,
> 
> and there is NO VOLTAGE GAIN after the reference. Zener-based
> 
> reference diodes are _much_ worse, and the LT3042 can hold
> 
> the candle even to 2V7-Zeners and most LEDs.
> 
> You can filter the LT3042 reference quite heavily, and there is
> 
> a startup circuit so you do not have to wait too long for the output voltage
> 
> to become stable.
> 
> 
> common Regulators:
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
>  
>      >
> 
> 
> Zeners: (Look at that awful super-precision ovenized LM399!)
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24411798996/in/album-72157662535945536/
>  
>      >
> 
> 
> LEDs:
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24354944411/in/album-72157662535945536/
>  
>      >
> 
> 
> King of the LEDs is hp/Avago/Broadcom HLMP6600, if it is still alive.
> 
> 
> I plan to repeat these measurements in the close future with a new 
> FET-based amplifier that
> 
> is not challenged by that stronger-than-1/f low frequency noise and that 
> can use cross correlation
> 
> additionally because of its missing noise current.
> 
> 
> regards, Gerhard.
> 
> 
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Re: [time-nuts] time-nuts Digest, Vol 180, Issue 22

[Bruce Griffiths]

The HP Journal article (page 20 March 1981 issue) on the 10811A agrees with Bob.
It also points out that the lack of activity dips due to coupled modes and a 
much smaller dependence of the frequency on the signal level  are advantages of 
the SC cut compared to the AT and BT cuts.

Bruce
> On 13 July 2019 at 00:06 Poul-Henning Kamp  wrote:
> 
> 
> 
> In message <2573d544-e3c9-4810-95c9-9e3a468ed...@leobodnar.com>, Leo Bodnar 
> wri
> tes:
> 
> >Here is a random selection of links to back my point of view that,
> >if you have noticed, contradicts Bob's.
> 
> Given that quartz resonators is still both science and art, I put
> my money on the guy who spent a whole career on quartz resonators
> over the guy who just walked out of the library :-)
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
> 
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Re: [time-nuts] High accuracy temp controller ckt

[Bruce Griffiths]

Figure 5 in http://www.wenzel.com/wp-content/uploads/Sub-pico-Multiplier.pdf
??
Bruce
> On 13 July 2019 at 05:23 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> If you do go the TEC route, plan on a fairly big power source :). There is a 
> Wenzel doc on doing a TEC based enclosure using a couple of die cast 
> boxes. The pictures don’t show what they used to drive the beast so part of 
> it would still be up to you. My search skills and their web site are not quite
> compatible so no link …. sorry !!!
> 
> Bob
> 
> > On Jul 12, 2019, at 12:12 PM, Javier Herrero  wrote:
> > 
> > Hello,
> > 
> > A TEC is good if you want to maintain the resistors at 25ºC, that seems the 
> > zero TC point for some precision low TCR resistors (for example, the Vishay 
> > VFCP or VSMP series)
> > 
> > Regards,
> > 
> > Javier
> > 
> > On 12/7/19 10:06, Dr. David Kirkby wrote:
> >> On Fri, 12 Jul 2019 at 08:07, Bernd Neubig  wrote:
> >> 
> >>> AXTAL has a miniature oven for heating precision resistors or other
> >>> components to a constant temperature. It is housed in a small DIP8 
> >>> package.
> >>> See attached AXR135 data sheet.
> >>> Optionally this device can be offered unsealed, ready for inserting the
> >>> component by yourself
> >>> 
> >>> Regards
> >>> Bernd
> >> 
> >> The resistors I am using are made by Caddock, are 1 M ohm & 10 M ohm, 0.01%
> >> tolerance and 5 ppm / deg C. They are much too large to fit in a DIP8
> >> package. A quick check with a ruler indicates that the 10 M ohm is 38 x 12
> >> mm and the 1 M ohm is 19 x 10 mm.
> >> 
> >> A quick photograph shows this half finished project. Unfortunately, even
> >> before I have finished it, I am wishing I had done a better job. However,
> >> my original reason for doing this was to check the stability of a data
> >> acquisition unit before sending it to Keysight. I think this will be good
> >> enough for that, but I could certainly have done a job with some thought.
> >> 
> >> The thermocouple is just meant to be a temperature sensor that dissipates
> >> no power. A thermistor or RTD buried in the polystyrene would have just got
> >> hot. The resistors should not get hot, as the power dissipated will be
> >> under 1 uW.
> >> 
> >> I also intend putting in a 100 M ohm resistor, but the specification of
> >> that is much poorer (5%, 100 ppm/ deg C. )
> >> 
> >> I partially read the paper mentioned. I note that the authors used a thermo
> >> electric cooler (TEC) as they wanted get low temperatures. I assume that
> >> for crystals or resistors dissipating little heat, a TEC would be
> >> unnecessary, and just a resistor acting as a heater would be fine. But will
> >> read some of the references. Obviously for controlling a crystal
> >> oscillator, or my resistor, stability is most important, whereas for the
> >> authors of the paper, stability was not their major concern.
> >> 
> >>> --
> >> Dr. David Kirkby,
> >> 
> >> ___
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> >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> >> and follow the instructions there.
> > 
> > -- 
> > -
> > Javier Herrero
> > Chief Technology Officer   EMAIL: 
> > jherr...@hvsistemas.com
> > HV Sistemas S.L.   PHONE: +34 949 
> > 336 806
> > Teide 4, Núcleo 1 Of. 0.1  FAX:   +34 949 
> > 336 792
> > 28703 San Sebastián de los Reyes - Madrid - Spain  WEB: 
> > http://www.hvsistemas.com
> > 
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Re: [time-nuts] Frequency Stability Analyzer - ZCDs

[Bruce Griffiths]

The LTC6957 is a better choice for squaring up sinewaves:
http://www.ko4bb.com/getsimple/index.php?id=phase-noise-and-other-measurements-with-a-timepod
CERN amongst others use it. The pin programmable filtering allows its bandwidth 
to be optimised to suit the input signal frequency and amplitude. This could be 
user selectable via front panel controls or under computer control.
Comparators are almost always noisier.
Oliver Collins wrote a paper on optimising such sine to square converters.
I extended the analysis to allow optimisation when the input noise of the 
cascaded stages arent equal.

Bruce
> On 27 July 2019 at 16:26 Glen English VK1XX  
> wrote:
> 
> 
> Hi
> 
> there is quite a bit done in this area of FPGAs, IDELAYS etc for this 
> application. and also quite a bit written already on TIMENUTS I find 
> from archives.
> 
>  From my POV, the pressure on the design is the input circuitry...My gut 
> is to start with a ADCMP572 and drive several FPGA pins  with PECL or 
> CML . BUT ! I have not thought about the problem very much, nor do I 
> have much experience with this application (and trying to be a little 
> modest here considering the company I am in) . The temperature 
> variability of the comparator hysteresis might be some issue with the 
> comparator.
> 
> I think the FPGA method certainly has many limits , compared to the 
> analog methods (dual slope phase comparators driving 24 bit ADCs etc, 
> vernier methods.) But my intuition is that a design that can leverage a 
> hybrid of analog  methods and some handy features available in modern 
> FPGAs can get the performance.
> 
> The idea is, to produce a general purpose high performance measurement 
> platform for HF region clocks, and pps, without having to resort to 
> buying an SR620.. analog front end, FPGA (VHDL) , drive for a standard 
> HD44780  LCD controller to display stuff, and  output (USB most likely) 
> for data analysis on a platform that has plenty of storage.
> 
> IDELAYS - there is good granuality (26ps Artix -1) (3 ps Ultrascale 
> Kintex)  , temperature stability is a bit average but that can be dealt 
> with. The IO delays are variable on the fly for some architectures. It 
> is not the whole story, but one of the bullets in the revolver in 
> acheiving the desired granuarity. There are several calibration options.
> 
> jitter added in the routing can be minimize with some manual placement 
> strategies
> 
> There  is an additional handle at the place and route level on 
> specifying constraint delays. This is pretty rough but if a good 
> calibration strategy can be developed, it is worthwhile. (IE conformance 
> to the constraint delays may vary from build to build so there needs to 
> be a bit of manual placement ) .
> 
> Yes, I think  trace delays are useful, although  rise time of the 
> devices together with PCB bandwidth muddies the water ,  and hence 
> uncertainty etc etc
> 
> I'd like to use a Lattice MACH X02 for this job but I think I will use a 
> Xilinx due to my familiarity  with them (and indeed, performance and 
> control of the synthesis tools) , and the speed.
> 
>     (i'm actually an RF person but FPGAs and DSP is an essential these 
> days) .
> 
> -glen
> 
> On 27/07/2019 11:49 AM, Hal Murray wrote:
> >> Was  considering  16 LVDS receivers and IDELAYS to emulate a single fast
> >> comparator,
> > I haven't done serious work with FPGAs in 10 or 15 years.
> >
> > That seems like an obvious hack, but it depends on the implementation 
> > details
> > inside the FPGA.  What's the granularity?  How much does it change from chip
> > to chip or over voltage and temperature?
> >
> > Has anybody published any data?
> >
> > --
> >
> > Another possibility is to use trace delays on the PCB.  You have a lumped
> > delay line with capacitance from the input pad.  This may not be practical 
> > for
> > short delays where the bond wires on the chip are not short relative to the
> > trace lengths.
> >
> >
> 
> 
> 
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Re: [time-nuts] atomic/chemical THz sampler

[Bruce Griffiths]

Electro-optic samplers are about the closest but they typically transform from 
time to spatial domain and have multibit resolution. The storage isnt atomic 
but in an image sensor attached to a spectroscometer.
http://beamdocs.fnal.gov/AD/DocDB/0025/002555/001/eos1.pdf


Bruce
> On 28 July 2019 at 17:37 Glen English VK1XX  
> wrote:
> 
> 
> OK research people...since this forum is loaded with bleeding edge 
> understanding,  Is there such a thing in the lab as a material that can 
> store, in a 2 level (1 bit) format (or more) , a discrete time 
> representation of some event ?
> 
> In my simple example (dream), an arrangement of some molecular or some  
> quantum storage medium, that can store an event at discrete intervals of 
> say, 100fs  ? That is, the duration of the storage might be 1nS, storing 
> the state of something, at 100fs intervals (example ) having a  (for 
> example) sample storage of 1 samples, and the ability to freeze that 
> event (in some atomic level memory) for later readout   once only or 
> continuously looped ?
> 
> No, I am not proposing this for my period /frequency analyser, I was 
> just wondering about super high speed digitization and storage of very 
> fast very short events.
> 
> -glen
> 
> 
> 
> 
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Re: [time-nuts] TAPR TIC Upgrade?

[Bruce Griffiths]

Probably only worth the effort if one were considering a higher resolution 
device intended to surpass that of the venerable HP5370A/B or equivalent.
Doable with off the TDC shelf parts but is there any demand?

Bruce
> On 15 August 2019 at 11:18 John Ackermann N8UR  wrote:
> 
> 
> In theory, making a new TICC that ran on an RPi could provide
> significantly more measurements per second, and more convenient I/O, but
> wouldn't affect the quality of the results.
> 
> I've thought a bit about an RPi-based TICC, but it's a significant
> redesign effort for limited gains.
> 
> John
> 
> 
> On 8/14/19 3:18 PM, Forrest Christian (List Account) wrote:
> > The TICC uses an Arduino mega clone, not a Raspberry Pi.
> > 
> > My understanding is that most of the magic happens on the shield board not
> > in the processor - the processor is just there to capture the data from the
> > shield and format and report it via the serial port.
> > 
> > On Wed, Aug 14, 2019 at 12:10 PM Perry Sandeen via time-nuts <
> > time-nuts@lists.febo.com> wrote:
> > 
> >> Yo Bubba Dudes!,
> >> I've just purchased a TAPR TIC module.  Now the new Raspberry Pi Model B
> >> has just been released.
> >> So my question is would there be any worthwhile advantage to replacing the
> >> TAPR unit with the new Model 4B?
> >> Regards,
> >> Perrier
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> >>
> > 
> > 
> 
> 
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Re: [time-nuts] Keysight N5511A - phase noise measurements down to theoretical-177 dBm/Hz

[Bruce Griffiths]

That should have been:

Its only necessary (as NIST have shown) to cool the splitters to reduce the 
correlated or anti-correlated thermal noise between splitter outputs. 
Everything else can run at ambient temperature. 

Bruce

> On 21 August 2019 at 21:13 Bruce Griffiths  wrote:
> 
> 
> Its only necessary (as NIST have shown) to cool the splitters to reduce the 
> correlated or anti-correlated noise between the outputs. Everything else can 
> run at ambient temperature. 
> 
> Bruce
> > On 21 August 2019 at 18:49 ed breya  wrote:
> > 
> > 
> > That's quite an impressive system. I guess it's a few generations beyond 
> > my 11729C.
> > 
> > One way to get overall performance to the limits of room temperature kT 
> > noise level, is to lower the T where you work. I wouldn't be surprised 
> > if some parts are TE-cooled, easily affordable in a big budget system. 
> > My first thought was maybe a bunch of stuff in a cryogenic system, but 
> > it looks like most pieces are modules in a rack mainframe, and not in a 
> > special environment. But, within the modules, I could picture some 
> > degree (PTP) of TE-cooling being included, giving some margin on the 
> > capabilities.
> > 
> > Ed
> > 
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Re: [time-nuts] Keysight N5511A - phase noise measurements down to theoretical-177 dBm/Hz

[Bruce Griffiths]

Its only necessary (as NIST have shown) to cool the splitters to reduce the 
correlated or anti-correlated noise between the outputs. Everything else can 
run at ambient temperature. 

Bruce
> On 21 August 2019 at 18:49 ed breya  wrote:
> 
> 
> That's quite an impressive system. I guess it's a few generations beyond 
> my 11729C.
> 
> One way to get overall performance to the limits of room temperature kT 
> noise level, is to lower the T where you work. I wouldn't be surprised 
> if some parts are TE-cooled, easily affordable in a big budget system. 
> My first thought was maybe a bunch of stuff in a cryogenic system, but 
> it looks like most pieces are modules in a rack mainframe, and not in a 
> special environment. But, within the modules, I could picture some 
> degree (PTP) of TE-cooling being included, giving some margin on the 
> capabilities.
> 
> Ed
> 
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Re: [time-nuts] Subject: Re: Keysight N5511A - phase noise measurements down to theoretical-177 dBm/Hz

[Bruce Griffiths]

With hot and cold noise sources perhaps?
Bruce
> On 24 August 2019 at 07:07 Perry Sandeen via time-nuts 
>  wrote:
> 
> 
> Gentlemen,
> A question for my curiosity and education.  Traditionally, the standard was 
> 10X better than what was being calibrated. 
> 
> Since this is at the theoretical limit, how might it be calibrated so the 
> numbers provided are accurate?
> Regards,
> Perrier
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Re: [time-nuts] Building a DMTD/phase noise set in the 21st century

[Bruce Griffiths]

I've only used an ultra low esr 33F supercap made in Korea in the source 
circuit of the input JFET on a preamp. 
Down to 10Hz at least it didn't appear to add significant noise to the 4nV/rtHz 
@10Hz preamp.

Bruce
> On 26 August 2019 at 13:52 Didier Juges  wrote:
> 
> 
> How do SuperCaps compare with electrolytics noise-wise?
> 
> Didier KO4BB
> 
> On Sun, Aug 25, 2019, 9:04 AM Gerhard Hoffmann  wrote:
> 
> >
> > Yes, these electrolytic capacitors can produce ugly effects.
> >
> > The winner is clearly the cheap
> >
> > < https://www.digikey.de/products/de?keywords=1189-1056-ND  >
> >
> >
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Re: [time-nuts] Building a DMTD/phase noise set in the 21st century

[Bruce Griffiths]

Mine exhibit a series resistance of a few tens of milliohms and the added 
thermal noise was insignificant. The manufacturer claimed to use nanostructured 
carbon electrodes.
The leakage current was also small

Bruce
> On 30 August 2019 at 11:19 Gerhard Hoffmann  wrote:
> 
> 
> 
> Am 26.08.19 um 04:47 schrieb Bruce Griffiths:
> > I've only used an ultra low esr 33F supercap made in Korea in the source 
> > circuit of the input JFET on a preamp.
> > Down to 10Hz at least it didn't appear to add significant noise to the 
> > 4nV/rtHz @10Hz preamp.
> 
> I had bought some at DK, but 30 Ohms or worse at AC in the source 
> produce >700pV/rtHz alone.
> 
> That would add (geometrically) to the 300 pV/rtHz of one Interfet 
> IF3601/3602
> 
> and spoil the pot, so I stayed with the multiple electrolytics with 
> milliOhms.
> 
> regards,
> 
> Gerhard
> 
> 
> 
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Re: [time-nuts] Building a DMTD/phase noise set in the 21st century

[Bruce Griffiths]

Actually the leakage of at least some standard electrolytic capacitors can be 
quite low if one waits long enough. I've seen a leakage as small as a few 
nanoamps after several minutes at room temperature with randomly selected 100uF 
capacitors.

Bruce
> On 30 August 2019 at 18:53 ed breya  wrote:
> 
> 
> I think there may be some confusion over the "super-capacitor" term. 
> Over the years, I've seen two types.
> 
> The most commonly encountered are the ones in consumer gear, for storing 
> charge to keep CMOS RAM alive during power outage and such, for a 
> reasonable amount of time. These may be from 47 mF to a Farad or so, and 
> have high ESR - they're not expected to dump huge charges, rather steady 
> uA range flows for the CMOS.
> 
> The other, more exotic kind are for bigger energy storage and power 
> conversion - these have very low ESR, like batteries, and may have lots 
> of Farads, but generally low working voltages, similar to a battery 
> cell. Higher working voltages are attained by stacking, with the 
> expected reduction of capacitance, of course.
> 
> I've only played with the former, since the latter were unusual and 
> expensive. One thing I can say is that the CMOS backup types are pretty 
> crappy capacitors for any use beyond their normal role, and they don't 
> last very long, in terms of service life - perhaps a decade or so. Most 
> that I've salvaged were found to be nearly totally open, like regular 
> old electrolytics after their juices have evaporated.
> 
> There may be more types nowadays, that overlap a number of applications.
> 
> In the situation I mentioned previously, I was planning on paralleling a 
> bunch of references to average out the noise somewhat, with combining 
> resistances around a hundred ohms. I had hoped to put a bunch of big 
> OSCONs in for filtering at the summing junction, but was wary of their 
> possible leakage currents lugging it down. I figured I could use 
> reasonable-valued, low leakage Ta caps instead, with enough low noise 
> amplifier gain to boost their effective values.
> 
> Ed
> 
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Re: [time-nuts] 5 Mhz to 10 Mhz and 25 Mhz

[Bruce Griffiths]

A frequency doubler and a frequency quintupler will be needed.

Options for the quintupler:

1) Convert to square wave and isolate the desired 25MHz output using filters. A 
bandpass filter is a poor choice if high phase stability is required. A high 
pass filter supplemented with series tuned shunt traps for the unwanted 
harmonics can provide higher phase stability

2) Wenzel's odd harmonic diode multiplier will also work:
http://techlib.com/files/RFDesign2.pdf

Options for the doubler

1) The NIST JFET based frequency doubler

2) A BJT based variant of the above

3) A diode based frequency doubler (full wave rectifier plus output filter)  


Bruce

> On 09 September 2019 at 00:02 Paul Bicknell  wrote:
> 
> 
> Dear all
> 
> Can any one point me in the direction of a circuit that can convert 
> 5 Mhz signal to give me 2 outputs one at 10 Mhz and another at 25 Mhz
> 
> 
> Regards Paul B
> 
> 
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Re: [time-nuts] 15Mhz in 10MHz out?

[Bruce Griffiths]

Dual JK flipflop configured as divide by 3 producing a 33% duty cycle 5MHz 
output which is filtered to extract the 10MHz second harmonic component.

Bruce
> On 18 September 2019 at 21:08 "David C. Partridge" 
>  wrote:
> 
> 
> Having seen the recent discussion of the NB3N502 and other PLLs for
> frequency multiplication.  I'm wondering if anyone knows of a similar
> *small* IC that will convert 15MHz to 10MHz ?
> 
> Why? My current modifications to the KS24361 output 10Mhz signals regardless
> of whether the unit has lock.   ISTR that the original 15MHz output was only
> enabled when the unit had lock.   I'd like to redo the PCB which I put in
> place of the 15MHz band-pass filter and replace it with one that takes 15Mhz
> an outputs 10Mhz.
> 
> Thanks
> David
> 
> 
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Re: [time-nuts] Question for my new GPSDO

[Bruce Griffiths]

Detecting the steep drop in oven heater current when the temperature regulator 
loop assumes control shouldn't require an extremely low tempco sensing resistor.

In principle PWM DACs can offer high resolution at relatively low cost, one 
tradeoff being the settling time of the low pass filter between the PWM output 
and the OCXO EFC input.

PWM DACs are inherently monotonic even when they have very high resolution.

Bruce 

> On 08 October 2019 at 10:06 Tobias Pluess  mailto:tobias.plu...@xwmail.ch > wrote:
> 
> 
> Hi Guys,
> 
> I am planning to make a new version of my own GPSDO. I have attached the 
> schematic of the OCXO and DAC. Because the stability of my previous design 
> was not yet optimal, I now chose better components; my main criteria was the 
> lowest tempco I found.
> As one can see, I plan to use the DAC8560, which is a 16-bit DAC having 
> an internal 2ppm/K voltage reference. Alternatively, the DAC8501 could be 
> used, which requires an external voltage reference for which I selected the 
> ADR441B (typically 1ppm/K).
> I have different OCXOs which I want to test; one of them requires a 0 to 
> 5V EFC voltage, and the other has 0 to 10V. By changing the gain of the two 
> noninverting amplifiers, both OCXOs can be fitted. The two 1k resistors make 
> the tuning range a bit smaller.
> The OpAmp I chose has 2.5 uV/K tempco.
> Besides that I have fitted an additional OpAmp to measure the OCXO 
> current. The Oscilloquartz STAR4 GPSDO I have has the same design; I assume 
> it measures the OCXO current to determine when the warmup time has elapsed.
> I was now consdering the tempco of the resistors involved. Should I use 
> there resistors having an especially low tempco, or are ordinary 1% resistors 
> fine?
> One last question; I have further analyzed the STAR4 design and I saw 
> that they are using a PWM DAC. Almost all GPSDOs I have ever seen uses PWM, 
> why do they do that? what is the advantage over a DAC similar to the one I 
> selected?
> 
> 
> Thanks for your comments,
> best
> Tobias
> HB9FSX
> 
> 
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Re: [time-nuts] Question for my new GPSDO

[Bruce Griffiths]

Some OCXOs have built in temperature outputs, sometimes its just a pir of wires 
connected to the ends of an internal thermistor.

Bruce

> On 08 October 2019 at 20:21 Tobias Pluess  wrote:
> 
> 
> Hi Bruce,
> 
> oh yes I know, for sure no special resistor will be used for the oven heater!
> By the way, many GPSDOs I have tested (e.g. Trimble Thunderbolt, STAR4) show 
> info about the OCXO temperature when connected via Lady Heather. Do you know 
> how they estimate the temperature? I checked almost every IC on the STAR4 PCB 
> and was unable to find a temperature sensor. Is it possible to estimate the 
> oven temperature from the current drawn? (for sure it is, but most likely it 
> will be strongly dependent on the particular OCXO used, I think).
> 
> OK, so using a PWM DAC is more a matter of cost than something else. In this 
> case I think I am fine with a DAC8501 or DAC8560, which are both based on a 
> resistor string, and therefore are also monotonic by design.
> 
> Tobias
> 
> 
> From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bruce 
> Griffiths [bruce.griffi...@xtra.co.nz]
> Sent: Tuesday, October 08, 2019 00:19
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Question for my new GPSDO
> 
> Detecting the steep drop in oven heater current when the temperature 
> regulator loop assumes control shouldn't require an extremely low tempco 
> sensing resistor.
> 
> In principle PWM DACs can offer high resolution at relatively low cost, one 
> tradeoff being the settling time of the low pass filter between the PWM 
> output and the OCXO EFC input.
> 
> PWM DACs are inherently monotonic even when they have very high resolution.
> 
> Bruce
> 
> > On 08 October 2019 at 10:06 Tobias Pluess  > mailto:tobias.plu...@xwmail.ch > wrote:
> >
> >
> > Hi Guys,
> >
> > I am planning to make a new version of my own GPSDO. I have attached 
> > the schematic of the OCXO and DAC. Because the stability of my previous 
> > design was not yet optimal, I now chose better components; my main criteria 
> > was the lowest tempco I found.
> > As one can see, I plan to use the DAC8560, which is a 16-bit DAC having 
> > an internal 2ppm/K voltage reference. Alternatively, the DAC8501 could be 
> > used, which requires an external voltage reference for which I selected the 
> > ADR441B (typically 1ppm/K).
> > I have different OCXOs which I want to test; one of them requires a 0 
> > to 5V EFC voltage, and the other has 0 to 10V. By changing the gain of the 
> > two noninverting amplifiers, both OCXOs can be fitted. The two 1k resistors 
> > make the tuning range a bit smaller.
> > The OpAmp I chose has 2.5 uV/K tempco.
> > Besides that I have fitted an additional OpAmp to measure the OCXO 
> > current. The Oscilloquartz STAR4 GPSDO I have has the same design; I assume 
> > it measures the OCXO current to determine when the warmup time has elapsed.
> > I was now consdering the tempco of the resistors involved. Should I use 
> > there resistors having an especially low tempco, or are ordinary 1% 
> > resistors fine?
> > One last question; I have further analyzed the STAR4 design and I saw 
> > that they are using a PWM DAC. Almost all GPSDOs I have ever seen uses PWM, 
> > why do they do that? what is the advantage over a DAC similar to the one I 
> > selected?
> >
> >
> > Thanks for your comments,
> > best
> > Tobias
> > HB9FSX
> >
> >
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Re: [time-nuts] Question for my new GPSDO

[Bruce Griffiths]

Consistency of the glitch independent of DAC output is more important than its 
size. A constant amplitude glitch occurring at the dac update rate is more 
benign in its effect than a glitch whose amplitude varies with DAC output.

Brruce
> On 16 October 2019 at 08:02 Attila Kinali  wrote:
> 
> 
> On Tue, 15 Oct 2019 18:57:30 +0200
> Attila Kinali  wrote:
> 
> > Assuming
> > your OCXO has a tuning range of 1ppm (I've seen 0.1 to 20ppm for OCXOs)
> > that would mean you have to controll the EFC voltage better than parts in 
> > 1e-9
> > or 30 bits. Yes, this is kind of unreallistic, but that's what the design
> > should aim for. If you acheive something around 24bits, you will be probably
> > close enough. (Note: that's 24bit resolution and stability over the
> > loop time constant. It is not 24bit absolute resolution)
> 
> Err.. correction: 1e-12 frequency control resolution with 1ppm EFC tuning
> range results in 1e-6 required EFC voltage control. Which in turn is 20bits.
> This is much saner requirement.
> 
> I thought something was off when I wrote this, but I was apparently not
> awake enough to realize that my calculation was wrong. Sorry about that.
> 
> 
>   Attila Kinali
> 
> -- 
>   The bad part of Zurich is where the degenerates
> throw DARK chocolate at you.
> 
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Re: [time-nuts] Question for my new GPSDO

[Bruce Griffiths]

If the DAC update rate isn't excessive a 2nV-sec glitch is unlikely to produce 
a significant perturbation at the output of the lowpass filter following the 
DAC.

Bruce
> On 16 October 2019 at 21:01 Attila Kinali  wrote:
> 
> 
> On Wed, 16 Oct 2019 15:04:31 +1300 (NZDT)
> Bruce Griffiths  wrote:
> 
> > Consistency of the glitch independent of DAC output is more important than 
> > its size. A constant amplitude glitch occurring at the dac update rate is 
> > more benign in its effect than a glitch whose amplitude varies with DAC 
> > output.
> 
> Yes. But it's actually not that bad. The glitch in the DAC is due to
> the CMOS switches in the DAC switching. Due to symmetry of the operation
> the glitch going from code A to code B will be the (almost) inverse of going
> from code B to code A. Which means they should (almost) cancel.
> 
> I can't find my notes from when I calculated this, but I remember that
> using an external CMOS switch had the same order of magnitude of uncertainty
> as using the DAC itself. And a few other effects would be also very close
> in magnitude. My conclusion was, considering that the back-of-envelope
> calculation of errors would result in a few bits more than necessary,
> the added complexity of using an external CMOS switch was probably not
> worth it. Of course, to be sure one would need to build both variants
> and measure them. Unfortunately, I don't have the means to do that.
> 
> Also, my guesstimate would be that using two DACs with metal-foil
> resistors for weighting would probably result in lower non-linearity.
> But the problem here is that the resistors add quite a bit of noise
> which in turn has to be accounted for.
> 
>   Attila Kinali
> 
> -- 
>   The bad part of Zurich is where the degenerates
> throw DARK chocolate at you.
> 
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Re: [time-nuts] 10MHz dist amps

[Bruce Griffiths]

Its measured noise floor is consistent with that expected from the noise 
specifications for the opamps employed.

Bruce

> On 24 October 2019 at 08:46 Tom Knox  wrote:
> 
> 
> Hi John;
> Amazing product, I did not realize you could use the TADD-1 for 100MHz 
> distribution.
> I do have a question, as someone who has tested most of the commercially 
> available distribution amps on the market TADD-1's -140dB @ 1Hz is among the 
> very very best best in the industry, (nothing is close for the price) but 
> compared to the very best the noise floor is a bit higher. Is this simply a 
> result of a raw board instead of a shielded enclosure?
> Thanks;
> 
> Tom Knox
> 
> 303-554-0307
> 
> act...@hotmail.com
> 
> "Peace is not the absence of violence, but the presence of Justice" Both MLK 
> and Albert Einstein
> 
> 
> From: time-nuts  on behalf of John 
> Ackermann. N8UR 
> Sent: Wednesday, October 23, 2019 11:54 AM
> To: ew via time-nuts 
> Subject: Re: [time-nuts] 10MHz dist amps
> 
> FWIW, I designed the TADD-1 to have equal length signal paths for all six 
> channels.
> 
> 73,
> John
> 
> On Oct 23, 2019, 1:01 PM, at 1:01 PM, "Bill Dailey, MD, MSEng, MSMI" 
>  wrote:
> >I am working in a project that requires me to have very similarly
> >phased
> >10mhz references (beamforming).
> >
> >Previously I just used splitters for 10MHz but now I am graduating to a
> >distribution amplifier.  Looking for suggestions/recommendations and
> >what I
> >should consider.  Distributing a Fury or a manually set a (May have
> >the
> >numbers wrong on this) oscillator.
> >
> >1. TADD-1 x 2
> >2. 5087A
> >3. 58502A
> >
> >2&3 are from the usual auction site and may have problems now or in the
> >future.
> >--
> >Doc
> >
> >Bill Dailey
> >KXØO
> >___
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Re: [time-nuts] A simple sampling DMTD

[Bruce Griffiths]

Merely selecting every 100th sample throws away the opportunity to reduce the 
effective ADC noise by digital filtering before decimation.

Bruce
> On 05 November 2019 at 10:08 Jan-Derk Bakker  wrote:
> 
> 
> Dear Scott,
> 
> You are entirely correct, sampling at 100ksps is mathematically the same as
> sampling at 10Msps and then decimating by a factor of 100. The reason I'm
> doing it in this way is driven by two practical considerations:
> 
> - my ADC, the LTC2140 (selected for bandwidth, dynamic range, aperture
> jitter and availability) has a pipelined design and cannot be clocked as
> slow as 100ksps without degrading performance
> - my CPU, the Atmel/Microchip XMega (selected for its peripherals, toolset
> support and familiarity for both me and my students) is an 8-bit AVR
> running at 30MHz and cannot directly process 10Msps
> 
> A simple D-flipflop based decimator was the easiest way to bridge this gap.
> The DMTD design has connectors for a (forthcoming) FPGA daughterboard to
> properly sinc-filter (and I/Q demodulate and...) the incoming samples.
> 
> Sincerely,
> 
> JD 'walk first, then run' B.
> 
> On Mon, Nov 4, 2019 at 6:38 PM W7SLS  wrote:
> 
> > Hello,
> >
> > (It has been a more few years since I designed / developed DSP for
> > spectrum analyzers for a major company, thanks for your patience.)
> >
> > I recall that:
> >
> > sample @ fs -> decimate (toss samples) by a factor of N
> >
> > is equivalent to
> >
> > sample @ fs / N
> >
> > If we wanted a lower sample rate, we would:
> >
> > sample @ fs  -> lowpass filter at (say) 80% of (fs/2) / N ->
> > decimate
> >
> > Otherwise all of the energy > 50% of (fs / N) gets aliased into your data.
> >
> > Why not just sample at 100 kHz?
> >
> > What am I missing ?
> >
> > Thanks for considering,
> > Scott W7SLS
> >
> > > On Nov 3, 2019, at 12:59 PM, Jan-Derk Bakker  wrote:
> > >
> > > Is this not caused by the fact that I'm currently subsampling the ADC
> > > (conversion rate 10Msps, rate into the microcontroller 100ksps by
> > dropping
> > > 99 put of 100 samples)?
> >
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[time-nuts] Re: E1938A phase noise improvement

[Bruce Griffiths]

Was it related to the cause of the hump in the PN plot vs offset frequency that 
the E1938A exhibits?

Bruce
> On 26/12/2021 17:56 Richard (Rick) Karlquist  wrote:
> 
>  
> I'm sure I said that ... a long time ago.  I can't remember now what the 
> fix was, but I am fairly sure it would only apply to phase noise at
> more than 1 kHz offset.  If anyone can jog my memory about it I might
> be able to remember the details.
> 
> Rick N6RK
> 
> On 12/25/2021 2:09 PM, Stewart Cobb wrote:
> > Rick Karlquist mentioned some time ago that the phase noise of the E1938A
> > could have been improved by a simple change, but the production managers
> > were unwilling to apply that change because there was no customer demand
> > for it.
> > 
> > What was that change, and is it feasible for a skilled hobbyist to make
> > that change on an individual existing unit or two?
> > 
> > Cheers!
> > --Stu
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