[time-nuts] Re: Low Phase Noise70 10 MHz bench signal source sought

[Richard (Rick) Karlquist]

He should be looking at Wenzel Associates and NEL.
Wenzel specs -170 dBc at 100 Hz offset.  Hope he has lots of money for 
this one.  Some of the NEL OCXO's are $5,000 and 6 months to 1 year

delivery.  Both vendors also sell noisier cheaper versions.
He needs to trade off noise vs offset vs cost vs delivery time.

If he is going to measure phase noise of another source with it,
he may need a VCOCXO to make a PLL.

Rick N6RK

On 4/1/2022 4:57 PM, Bob kb8tq wrote:

Hi

Rb and low phase noise ( at least far removed ) are sort of mutually
exclusive specs. You need to pick one …

Assuming the decision is to go for the -170 dbc/Hz spec, Congratulations
you are buying on OCXO. Not quite clear which OCXO, but it’s pretty likely
to be an OCXO. (Yes, there are exceptions, but they are rare enough to be
in the “don’t bother” category),

Next step would be to decide on the max offset that needs to cut in at.
100 Hz is into the “crazy/ not gonna happen” region. 1KHz is unlikely.
10 KHz is doable. 100 KHz relaxes things a bit.

While the “buy a bunch and test” approach works for things like ADEV,
it probably isn’t the best approach for this spec. If you buy a bunch of this
or that OCXO, their 10KHz phase noise *should* be pretty consistent.
Sorting to get 2 db … nope, not worth it.  It *is* a pretty good bet that
a commercial spec at 10K will be beat by 3 to 6 db.

What to buy? Head off to the spec sheets on whatever you see on eBay
and make some guesses.

Bob






On Apr 1, 2022, at 5:12 PM, Joseph Gwinn  wrote:

I'm looking for suggestions for AC-powered 10 MHz sinewave laboratory
signal sources with very low phase noise, having a noise floor below
-170 dBc/Hz.  Rubidium is desired, but not essential.  Reliability
and durability in lab use is essential.

Which makes and models should I consider purchasing?

I like the SRS model FS725, but its noise floor is too high at -150
dBm/Hz, 20 dB noisier than many things I may wish to measure.


Thanks,

Joe Gwinn
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[time-nuts] Re: Low Phase Noise70 10 MHz bench signal source sought

[Bob kb8tq]

Hi

Rb and low phase noise ( at least far removed ) are sort of mutually 
exclusive specs. You need to pick one … 

Assuming the decision is to go for the -170 dbc/Hz spec, Congratulations 
you are buying on OCXO. Not quite clear which OCXO, but it’s pretty likely
to be an OCXO. (Yes, there are exceptions, but they are rare enough to be 
in the “don’t bother” category), 

Next step would be to decide on the max offset that needs to cut in at. 
100 Hz is into the “crazy/ not gonna happen” region. 1KHz is unlikely. 
10 KHz is doable. 100 KHz relaxes things a bit. 

While the “buy a bunch and test” approach works for things like ADEV, 
it probably isn’t the best approach for this spec. If you buy a bunch of this
or that OCXO, their 10KHz phase noise *should* be pretty consistent. 
Sorting to get 2 db … nope, not worth it.  It *is* a pretty good bet that 
a commercial spec at 10K will be beat by 3 to 6 db. 

What to buy? Head off to the spec sheets on whatever you see on eBay
and make some guesses. 

Bob





> On Apr 1, 2022, at 5:12 PM, Joseph Gwinn  wrote:
> 
> I'm looking for suggestions for AC-powered 10 MHz sinewave laboratory 
> signal sources with very low phase noise, having a noise floor below 
> -170 dBc/Hz.  Rubidium is desired, but not essential.  Reliability 
> and durability in lab use is essential.
> 
> Which makes and models should I consider purchasing?  
> 
> I like the SRS model FS725, but its noise floor is too high at -150 
> dBm/Hz, 20 dB noisier than many things I may wish to measure.  
> 
> 
> Thanks,
> 
> Joe Gwinn
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[time-nuts] Low Phase Noise 10 MHz bench signal source sought

[Joseph Gwinn]

I'm looking for suggestions for AC-powered 10 MHz sinewave laboratory 
signal sources with very low phase noise, having a noise floor below 
-170 dBc/Hz.  Rubidium is desired, but not essential.  Reliability 
and durability in lab use is essential.

Which makes and models should I consider purchasing?  

I like the SRS model FS725, but its noise floor is too high at -150 
dBm/Hz, 20 dB noisier than many things I may wish to measure.  


Thanks,

Joe Gwinn
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[time-nuts] Re: 32.768Khz Crystal Trimming

[Dan Kemppainen]

All,

Ahhh, Yes. Checking notes, during the initial build I slapped a pair of 
10pF caps down (all I had on hand) just to get the RTCC oscillators 
somewhat working. I can see now that is WAY under needed capacitance.


Measurements are taken right in the micro, so no external leads to 
influence the board. A serial debug line spits out the difference in 
elapsed time for the RTCC and time derived from the 10Mhz EXT REF 
(GPSDO). (No extra wires/leads etc.)


Honestly this RTCC doesn't need to be stellar. It's more of a holdover 
oscillator when the EXT CLK is lost. But, this is time-nuts and all, so 
might as well squeeze everything out of it! :)




Bernd,

Your post, and rule of thumb are what I was looking for. I will 
certainly archive this in my notes. This should be good enough to save 
destroying the board by soldering/de-soldering many 0603 SMT caps.



Thanks to all who replied. This should be enough to keep me busy over 
the weekend!


Dan



On 4/1/2022 12:26 PM, time-nuts-requ...@lists.febo.com wrote:

Subject:
[time-nuts] Re: 32.768Khz Crystal Trimming
From:
"Bernd Neubig" 



If you do not want to make it a time-nuts style research project, but just
look for a quick fix - here is a rule of thumb:
This kind of crystal usually has a trimming sensitivity of around -10
ppm/pF. This means, if you increase the value of both capacitors on either
side by 2 pF will increase the load capacitance by 1 pF and thus lower the
frequency by  about 10 ppm.
If you need to vary one cap slightly more than the other, (to get a finer
resolution), please use the one at the output side of the on-chip oscillator
stage.
Take care of the start-up margin (safety to get a reliable start-up after
power on). The larger the capacitors, the lower becomes the margin,
sometimes the margin drops rather quickly. Therefore, after having made the
changes, test the start-up behavior by switching on and off several times,
preferably with a slow voltage ramp.

Enjoy the crystal world (as I did for the last 45 years and still doing).

Bernd

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[time-nuts] Surplus uBlox LEA-4T modules

[Gregory Beat via time-nuts]

A Search at eBay or a general Google search on the Internet
will reveal a number of older GPS modules used for timing (used & new)

A recent eBay search revealed a group of five (5) uBlox-4T modules for $24 
(free ship).
eBay Auction number: 203426846312

uBlox LEA-4x series GPS receiver Data Sheet
https://www.mikrocontroller.net/attachment/26089/LEA-4x_Data_Sheet_GPS.G4-MS4-06143_.pdf

The LEA-4T is a 16-channel ANTARIS®4 positioning engine released in 2007.
http://datasheet.buhieen.net/LEA-4T.pdf

The LEA-4T supports precision GPS timing and raw measure- ment data for 
demanding positioning applications. It features a Time Mode function whereby 
the GPS receiver assumes a stationary 3D position, whether programmed manually 
or de- termined by an initial self-survey. Stationary operation enables GPS 
timing with only one visible satellite and eliminates timing errors which 
otherwise result from positioning errors. The accuracy of the time pulse is as 
good as 50 ns, synchronized to GPS or UTC time. An accuracy of 15 ns is 
achievable by using the quantization error information to compensate the granu- 
larity of the time pulse. The built-in 2-channel time mark and counter unit 
provides precise time measurement of external interrupt signals.
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[time-nuts] Re: 32.768Khz Crystal Trimming

[Bob kb8tq]

Hi

The typical 32 KHz crystal has a parabolic tempco. It peaks at kinda 
sorta room temperature. This makes it work pretty well on a normal 
wrist. 

As you get away from ~ 25C, the frequency drops. Since it’s a 
parabola, the further away from room you get the faster it drops. 
Something in the 1 to 2 ppm / C is not a bad guess for typical “on a 
board” sort of temperatures. 

It’s pretty hard to predict what temperature the board you just made 
will operate at out in the field. Thus there are limits on what you can 
expect from a watch crystal. 

10 seconds over 100,000 seconds ( so a bit over a day) is hundred
ppm. That’s a lot of shift and yes, it’s worth taking care of that
sort of offset. 

At 1 second per 100,000 you are at 10 ppm. That is in the range of 
“questionable temperature”. You can get it set that well ( or better) 
on your bench. As soon as it leaves your bench …. all that work may 
not have been worth the effort. 

No, temperature isn’t the only variable. The crystals have a calibration
tolerance at room ( +/- 20 ppm on this crystal). They most certainly do 
age ( 3 ppm  / year on this one). They also shift when you solder them 
into a board. That shift may or may not relax over the next few days. 

If your application *needs* a second a day sort of performance, 
something sort of improvement over a basic watch crystal will be 
needed. At the very least, the 20 ppm cal tolerance will need to be 
adressed. 

Bob

> On Apr 1, 2022, at 12:34 PM, Richard (Rick) Karlquist  
> wrote:
> 
> No one mentioned tempco, so I will.  Ideally you should do your
> calibration at a temperature corresponding to the long term
> average in your workshop.  If the crystal is in a piece of
> equipment with a temperate rise, it should be accounted for,
> and then going forward you have to leave the equipment powered
> up 24/7.  The crystal is probably a tuning fork, meaning it
> won't be AT cut.  It may have a substantial tempco around
> room temp.  In which case that old time-nuts insult may apply:
> 
> "congratulations, nice thermometer."
> 
> Rick N6RK
> 
> BTW, I go back 48 years with crystals.
> 
> On 4/1/2022 8:30 AM, Bernd Neubig wrote:
>> Hi,
>> If you do not want to make it a time-nuts style research project, but just
>> look for a quick fix - here is a rule of thumb:
>> This kind of crystal usually has a trimming sensitivity of around -10
>> ppm/pF. This means, if you increase the value of both capacitors on either
>> side by 2 pF will increase the load capacitance by 1 pF and thus lower the
>> frequency by  about 10 ppm.
>> If you need to vary one cap slightly more than the other, (to get a finer
>> resolution), please use the one at the output side of the on-chip oscillator
>> stage.
>> Take care of the start-up margin (safety to get a reliable start-up after
>> power on). The larger the capacitors, the lower becomes the margin,
>> sometimes the margin drops rather quickly. Therefore, after having made the
>> changes, test the start-up behavior by switching on and off several times,
>> preferably with a slow voltage ramp.
>> Enjoy the crystal world (as I did for the last 45 years and still doing).
>> Bernd
>> -Ursprüngliche Nachricht-
>> Von: Dan Kemppainen [mailto:d...@irtelemetrics.com]
>> Gesendet: Freitag, 1. April 2022 14:47
>> An: time-nuts@lists.febo.com
>> Betreff: [time-nuts] 32.768Khz Crystal Trimming
>> Hi,
>> I've got a 32.768Khz (USA number format) crystal on a RTCC oscillator of a
>> small micro, and it's running fast. Around 10 seconds per day or so.
>> This is a bit more than an order of magnitude more than the datasheet
>> states.
>> The 9 seconds per day error should be a good measurement. The RTCC is
>> running a 1 second counter, and that's being compared to a 1 second counter
>> derived by clocking the micro from a 10Mhz EXT clock reference.
>> This is consistent between multiple copies of the board.
>> I'm assuming, the C1/C2 load capacitors to ground needs to be higher in
>> value to trim that oscillator closer to the correct frequency. Is this
>> correct? Any quick back of the napkin calculations how much additional load
>> capacitance would be needed?
>> For Ref, this is the crystal:
>> https://abracon.com/Resonators/ABS06.pdf
>> ABS06-32.768KHZ-1-T
>> Thanks,
>> Dan
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[time-nuts] Re: The STM32 GPSDO, a short presentation

[Bob kb8tq]

Hi

GPS modules tend to be “accuracy rated” in terms of what they
do when fed with a signal generator. The “accuracy” is the departure
from the reference pulse out of the generator. Oddly enough it does 
not include all of the delays involved ( yes that’s a bit weird). 

When you feed them with real signals from real sats, those numbers
are only a guess. Under various conditions they may be a pretty bad
guess. How well the GPSDO is at recognizing / catching these conditions 
and dealing with them will impact its accuracy.

Bob

> On Apr 1, 2022, at 9:53 AM, André Balsa  wrote:
> 
> So reading a little bit about the "three cornered hat method", it assumes
> the errors in the three datasets are not correlated, which in the case of
> testing three different GPSDOs is obviously not the case. However we
> already have estimates of the magnitude of the error introduced by the GPS
> PPS: I think many of you have already done this kind of measurement and
> u-blox themselves have an old paper about their Neo-M6 receivers. So we can
> put an upper bound on the magnitude of the error introduced by the GPS PPS
> and then subtract it from the overall performance of the GPSDOs being
> tested.
> But I guess I am at this point quite off-topic in relation to my original
> post.
> Just a note to say that I am coding right now the option to print once per
> second extensive data in tabulated format instead of the human-readable
> format that is presently output, I should upload this new firmware tomorrow
> afternoon after some testing.
> 
> This is the data that will be presented in tab-delimited format:
> 
> STM32 GPSDO reporting tab delimited fields
> 
> Line no. (0 if no position fix, increments by one each second if position
> fix)
> timestamp (UTC)
> uptime (days hours mins secs)
> 64-bit count
> frequency (Hz)
> 10s freq. avg. (one decimal) (Hz)
> 100s freq. avg. (two decimals) (Hz)
> 1,000s freq. avg. (three decimals) (Hz)
> 10,000s freq. avg. (four decimals) (Hz)
> no. of sats
> HDOP (meters)
> PWM (16-bit, 1-65535)
> PWM adc mov. avg. (V)
> Vcc adc mov. avg. (5.0V nominal)
> Vdd adc mov. avg. (3.3V nominal)
> BMP280 Temp. (C)
> BMP280 Atm. Pressure (hPa)
> AHT20 Temp. (C)
> AHT20 Humidity (%)
> INA219 OCXO Voltage (5.05V nominal)
> INA219 OCXO Current (2A maximum)
> TIC (10-bit, 1024ns max)
> 
> When a value is not available, the field contains "0".
> 
> 
> 
> 
> 
> On Fri, Apr 1, 2022 at 2:43 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> The drift used in the original example is just one of many many things
>> that can come up. There are a lot of “corner cases” in GPSDO design.
>> The constellation does “this” and they all react. Ideally they would react
>> to suppress whatever the issue is. It does not always work out that way.
>> 
>> This is not in any way unique to GPSDO’s. You might have a set of OCXO’s or
>> Rb’s as the elements in a three corner hat that all had the same tempco
>> slope
>> and magnitude. In a normal lab, that could create a problem.
>> 
>> The first time I saw the topic debated it was at FCS. It was in relation
>> to the
>> Cs standards used in national time scales ….. ( and why having them all
>> one
>> model from one company wasn’t a great idea ).
>> 
>> Bob
>> 
>>> On Mar 31, 2022, at 10:06 PM, Chris Caudle <6807.ch...@pop.powweb.com>
>> wrote:
>>> 
>>> On Thu, March 31, 2022 6:28 pm, Bob kb8tq wrote:
 Consider the case:
 
 GPS shifts ( possibly due to any of a number of issues).
 All three modules "move" forward in time by 15 or 20 ns
 over some time period.
 The GPSDO's all do their thing and shift frequency by
 the appropriate amount.
 
 Since all three devices in your three corner hat did the
 same thing at the same time, all of the delta this / delta
 that numbers just sit there.
 They do not show the frequency shift at all.
>>> 
>>> That would matter if you wanted to know how good your clock or oscillator
>>> was (in some sort of absolute sense).
>>> If all you wanted to know was how good your GPSDO was, wouldn't that
>>> common mode behavior just fall into an intrinsic aspect of using GPS?
>>> I think in the case that you want to know how good your particular GPSDO
>>> is at being a GPS disciplined thing, compare to other models (e.g.
>>> Thunderbolt, Jackson Labs, HP, etc.) and you can get a good idea of how
>>> well it performs given the limitations that it has to use GPS to
>> function.
>>> 
>>> The bigger problem I see with the original proposal were that there were
>>> too many of the new design involved, I think three if the model under
>>> design, and one other homebrew model, so there could be common mode
>>> problems caused by e.g. a firmware error (frequency offset in a FLL comes
>>> to mind) that would be hidden by having all the 3 models under test being
>>> the same.
>>> By testing e.g. one new model, one Thunderbolt, and one Jackson Labs it
>>> should at least be possible to tease out what behavior is unique to the
>>> new STM32 

[time-nuts] Re: 32.768Khz Crystal Trimming

[Richard (Rick) Karlquist]

No one mentioned tempco, so I will.  Ideally you should do your
calibration at a temperature corresponding to the long term
average in your workshop.  If the crystal is in a piece of
equipment with a temperate rise, it should be accounted for,
and then going forward you have to leave the equipment powered
up 24/7.  The crystal is probably a tuning fork, meaning it
won't be AT cut.  It may have a substantial tempco around
room temp.  In which case that old time-nuts insult may apply:

"congratulations, nice thermometer."

Rick N6RK

BTW, I go back 48 years with crystals.

On 4/1/2022 8:30 AM, Bernd Neubig wrote:

Hi,

If you do not want to make it a time-nuts style research project, but just
look for a quick fix - here is a rule of thumb:
This kind of crystal usually has a trimming sensitivity of around -10
ppm/pF. This means, if you increase the value of both capacitors on either
side by 2 pF will increase the load capacitance by 1 pF and thus lower the
frequency by  about 10 ppm.
If you need to vary one cap slightly more than the other, (to get a finer
resolution), please use the one at the output side of the on-chip oscillator
stage.
Take care of the start-up margin (safety to get a reliable start-up after
power on). The larger the capacitors, the lower becomes the margin,
sometimes the margin drops rather quickly. Therefore, after having made the
changes, test the start-up behavior by switching on and off several times,
preferably with a slow voltage ramp.

Enjoy the crystal world (as I did for the last 45 years and still doing).

Bernd


-Ursprüngliche Nachricht-
Von: Dan Kemppainen [mailto:d...@irtelemetrics.com]
Gesendet: Freitag, 1. April 2022 14:47
An: time-nuts@lists.febo.com
Betreff: [time-nuts] 32.768Khz Crystal Trimming

Hi,

I've got a 32.768Khz (USA number format) crystal on a RTCC oscillator of a
small micro, and it's running fast. Around 10 seconds per day or so.
This is a bit more than an order of magnitude more than the datasheet
states.

The 9 seconds per day error should be a good measurement. The RTCC is
running a 1 second counter, and that's being compared to a 1 second counter
derived by clocking the micro from a 10Mhz EXT clock reference.
This is consistent between multiple copies of the board.

I'm assuming, the C1/C2 load capacitors to ground needs to be higher in
value to trim that oscillator closer to the correct frequency. Is this
correct? Any quick back of the napkin calculations how much additional load
capacitance would be needed?

For Ref, this is the crystal:
https://abracon.com/Resonators/ABS06.pdf
ABS06-32.768KHZ-1-T

Thanks,
Dan


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[time-nuts] Re: disciplning natural phenomena

[Poul-Henning Kamp]

Lux, Jim writes:

> Can one discipline a geyser to an external source?
>
>a) I assume there's some data somewhere on eruption timing - sure, Old 
>Faithful is quite regular, sufficiently that they can say "the next 
>eruption will occur at" and people will gather and watch it.

Last I heard, they "seeded" it by pouring some harmless household
chemical (soap?) into it ?  I was told that this also regularized the
size of each "performance".

-- 
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: disciplning natural phenomena

[Bob kb8tq]

Hi

Well, specific to Old Faithful ….

They look at the current eruption and rate it for height and duration. 
Based on that rating, they make a guess about the wait for the next 
one. Their guess is typically a +/- 10 minute sort of thing. Very much 
like predicting the weather. 

https://www.nps.gov/yell/planyourvisit/geyser-activity.htm 


Bob

> On Apr 1, 2022, at 9:09 AM, Lux, Jim  wrote:
> 
> As I re-read Fleming's "You Only Live Twice" last night, which features a 
> geyser that is "regulated" by a valve of some sort I was intrigued by this 
> idea:
> 
> Can one discipline a geyser to an external source?
> 
> a) I assume there's some data somewhere on eruption timing - sure, Old 
> Faithful is quite regular, sufficiently that they can say "the next eruption 
> will occur at" and people will gather and watch it.  But what's the ADEV? As 
> a kid in the early 70s, I didn't think to ask this question, and neither 
> Allan nor Leeson seem to mention it in their papers from 1966.  There is a 
> lot of variation in timing performance of various geysers, though.  Old 
> Faithful *is* regular, and in a place where it's watchable.
> 
> b) Are periodic geysers actually regulatable ?- From the little I know about 
> how they work, I would think the eruption frequency depends on things like 
> the water temperature and flow. It's also possible that the valve in 
> Fleming's novel is purely fictional, because it serves as part of a plot 
> device at the end (much like closing off the safety valve on a boiler).
> 
> Or, are geysers an example of a chaotic system that is only seemingly regular 
> in some sense? That is, it's not like a VCO, with a consistent and well 
> defined relation between the control input and the period. Changing the 
> control input may change the period in an unpredictable way. Some geysers 
> stop working if the surrounding hydrology changes. Or is that simply that the 
> Q of the oscillator is so high that it's easy to "get out of operating 
> range".  That would be like trying to discipline a spurious parasitic 
> oscillation in an amplifier.
> 
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[time-nuts] Re: disciplning natural phenomena +1/f of transistors

[ghf]

Am 2022-04-01 15:09, schrieb Lux, Jim:

As I re-read Fleming's "You Only Live Twice" last night, which
features a geyser that is "regulated" by a valve of some sort I was
intrigued by this idea:

Can one discipline a geyser to an external source?


The original Geysir in Island has become lazy. It takes an
earthquake to trigger it.

It's smaller neighbor, the Strokkur, can be triggered by throwing in
some soft soap, but that is forbidden now. Running free, it happens
every 6 minutes or so. Sorry, I did not measure adev etc.

<
https://www.flickr.com/photos/137684711@N07/4005253/in/album-72157688304045365/ 
  >


cheers, Gerhard

ps.  does anybody here have 1/f data of "interesting" transistors?
(not much hope)
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[time-nuts] Re: disciplning natural phenomena

[Tom Van Baak]

I've attached the ADEV plot from 11 years of Old Faithful data (2001 to 
2011).


For the data and also a deep dive into geyser statistics see this 
wonderful article:


http://www.stat.yale.edu/~jah49/Pictures_in_R/Fickle_Old_Faithful/OldFaithful.pdf

These papers might also be interesting to you:

"Triggering and modulation of geyser eruptions in Yellowstone National 
Park by earthquakes, earth tides, and weather"

https://digitalcommons.lsu.edu/cgi/viewcontent.cgi?article=2191=geo_pubs

"A Look at Some Data on the Old Faithful Geyser"
https://doi.org/10.2307/2347385

"Model for the eruption of the Old Faithful geyser, Yellowstone National 
Park"

https://www.geosociety.org/gsatoday/archive/23/6/pdf/i1052-5173-23-6-4.pdf

"A History of the Old Faithful Area with Chronology, Maps, and Executive 
Summary"

http://npshistory.com/publications/yell/old-faithful-area-history.pdf

For current and recent information see:

https://www.geysertimes.org/geyser.php?id=Old+Faithful
https://www.geysertimes.org/data.php
https://www.geysertimes.org/analysis.php
https://www.geysertimes.org/map.php

And of course there's a webcam:

https://yellowstone.net/geysers/old-faithful/
https://yellowstone.net/geysers/old-faithful-webcam/

/tvb


On 4/1/2022 6:09 AM, Lux, Jim wrote:
As I re-read Fleming's "You Only Live Twice" last night, which 
features a geyser that is "regulated" by a valve of some sort I was 
intrigued by this idea:


Can one discipline a geyser to an external source?

a) I assume there's some data somewhere on eruption timing - sure, Old 
Faithful is quite regular, sufficiently that they can say "the next 
eruption will occur at" and people will gather and watch it. But 
what's the ADEV? As a kid in the early 70s, I didn't think to ask this 
question, and neither Allan nor Leeson seem to mention it in their 
papers from 1966.  There is a lot of variation in timing performance 
of various geysers, though.  Old Faithful *is* regular, and in a place 
where it's watchable.


b) Are periodic geysers actually regulatable ?- From the little I know 
about how they work, I would think the eruption frequency depends on 
things like the water temperature and flow. It's also possible that 
the valve in Fleming's novel is purely fictional, because it serves as 
part of a plot device at the end (much like closing off the safety 
valve on a boiler).


Or, are geysers an example of a chaotic system that is only seemingly 
regular in some sense? That is, it's not like a VCO, with a consistent 
and well defined relation between the control input and the period. 
Changing the control input may change the period in an unpredictable 
way. Some geysers stop working if the surrounding hydrology changes. 
Or is that simply that the Q of the oscillator is so high that it's 
easy to "get out of operating range".  That would be like trying to 
discipline a spurious parasitic oscillation in an amplifier.


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[time-nuts] Re: The STM32 GPSDO, a short presentation

[Erik Kaashoek]

Nice, I'm trying to do something similar. But without the PICdiv or the 
TIC measurement. Only the GPS PPS into the STM32 and the stabilized PPS 
is generated by a timer in the STM32

First step was to measure against the running average of the GPS PPS.
As can be seen in attached Timeplot measurement the phase error is (when 
temperatures stabilized) in the order of 10ns.

Erik.

On 31-3-2022 12:52, André Balsa wrote:

Hello fellow time-nuts,

My second post to the list. I just wanted to mention that the STM32 GPSDO
is a 100% Open Source project, fully documented in the GitHub repository
https://github.com/AndrewBCN/STM32-GPSDO and the EEVblog thread
https://www.eevblog.com/forum/projects/yet-another-diy-gpsdo-yes-another-one/
. Also some details are available about the firmware in the stm32duino
forum thread https://www.stm32duino.com/viewtopic.php?f=10=1031

The project has some unique features compared to any other commercial or
hobby GPSDO and it is still very much in full swing and actively developed
not only by myself but also by a few collaborators.

One of the unique features of the STM32 GPSDO is that it uses both a PLL
and an FLL. I developed the 100% software FLL around May 2021 and for the
PLL I have borrowed Lars Walenius genius TIC design with Erik Kaashoek's
modifications (using a 74HC74 instead of a 74HC4046) (WIP). I am also using
a picDIV by Tom Van Baak to generate a UTC synchronized PPS (again, WIP).

The project can be assembled on a breadboard in one afternoon provided one
has all the parts and it works "out of the box". The BOM total cost stands
at around 45€ for the basic version and 70€ with all the bells and whistles.

The firmware leverages the Arduino programming environment and the hundreds
of available libraries, and it is written with the express purpose of being
easy to understand, maintain and further develop. It now stands at around
1700 lines of C/C++ code with extensive comments.

The main communications channel for this project is the EEVblog thread
mentioned above.

Greetings from France,
Andrew
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[time-nuts] Re: The STM32 GPSDO, a short presentation

[André Balsa]

So reading a little bit about the "three cornered hat method", it assumes
the errors in the three datasets are not correlated, which in the case of
testing three different GPSDOs is obviously not the case. However we
already have estimates of the magnitude of the error introduced by the GPS
PPS: I think many of you have already done this kind of measurement and
u-blox themselves have an old paper about their Neo-M6 receivers. So we can
put an upper bound on the magnitude of the error introduced by the GPS PPS
and then subtract it from the overall performance of the GPSDOs being
tested.
But I guess I am at this point quite off-topic in relation to my original
post.
Just a note to say that I am coding right now the option to print once per
second extensive data in tabulated format instead of the human-readable
format that is presently output, I should upload this new firmware tomorrow
afternoon after some testing.

This is the data that will be presented in tab-delimited format:

STM32 GPSDO reporting tab delimited fields

Line no. (0 if no position fix, increments by one each second if position
fix)
timestamp (UTC)
uptime (days hours mins secs)
64-bit count
frequency (Hz)
10s freq. avg. (one decimal) (Hz)
100s freq. avg. (two decimals) (Hz)
1,000s freq. avg. (three decimals) (Hz)
10,000s freq. avg. (four decimals) (Hz)
no. of sats
HDOP (meters)
PWM (16-bit, 1-65535)
PWM adc mov. avg. (V)
Vcc adc mov. avg. (5.0V nominal)
Vdd adc mov. avg. (3.3V nominal)
BMP280 Temp. (C)
BMP280 Atm. Pressure (hPa)
AHT20 Temp. (C)
AHT20 Humidity (%)
INA219 OCXO Voltage (5.05V nominal)
INA219 OCXO Current (2A maximum)
TIC (10-bit, 1024ns max)

When a value is not available, the field contains "0".





On Fri, Apr 1, 2022 at 2:43 PM Bob kb8tq  wrote:

> Hi
>
> The drift used in the original example is just one of many many things
> that can come up. There are a lot of “corner cases” in GPSDO design.
> The constellation does “this” and they all react. Ideally they would react
> to suppress whatever the issue is. It does not always work out that way.
>
> This is not in any way unique to GPSDO’s. You might have a set of OCXO’s or
> Rb’s as the elements in a three corner hat that all had the same tempco
> slope
> and magnitude. In a normal lab, that could create a problem.
>
> The first time I saw the topic debated it was at FCS. It was in relation
> to the
> Cs standards used in national time scales ….. ( and why having them all
> one
> model from one company wasn’t a great idea ).
>
> Bob
>
> > On Mar 31, 2022, at 10:06 PM, Chris Caudle <6807.ch...@pop.powweb.com>
> wrote:
> >
> > On Thu, March 31, 2022 6:28 pm, Bob kb8tq wrote:
> >> Consider the case:
> >>
> >> GPS shifts ( possibly due to any of a number of issues).
> >> All three modules "move" forward in time by 15 or 20 ns
> >> over some time period.
> >> The GPSDO's all do their thing and shift frequency by
> >> the appropriate amount.
> >>
> >> Since all three devices in your three corner hat did the
> >> same thing at the same time, all of the delta this / delta
> >> that numbers just sit there.
> >> They do not show the frequency shift at all.
> >
> > That would matter if you wanted to know how good your clock or oscillator
> > was (in some sort of absolute sense).
> > If all you wanted to know was how good your GPSDO was, wouldn't that
> > common mode behavior just fall into an intrinsic aspect of using GPS?
> > I think in the case that you want to know how good your particular GPSDO
> > is at being a GPS disciplined thing, compare to other models (e.g.
> > Thunderbolt, Jackson Labs, HP, etc.) and you can get a good idea of how
> > well it performs given the limitations that it has to use GPS to
> function.
> >
> > The bigger problem I see with the original proposal were that there were
> > too many of the new design involved, I think three if the model under
> > design, and one other homebrew model, so there could be common mode
> > problems caused by e.g. a firmware error (frequency offset in a FLL comes
> > to mind) that would be hidden by having all the 3 models under test being
> > the same.
> > By testing e.g. one new model, one Thunderbolt, and one Jackson Labs it
> > should at least be possible to tease out what behavior is unique to the
> > new STM32 device.
> >
> > --
> > Chris Caudle
> >
> >
> >
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[time-nuts] Re: Self monitoring

[André Balsa]

In summary, to measure the accuracy or stability of any clock, you always
need... a better clock. Or you can use the "three cornered hat" method, but
it requires that the accuracy or stability of the three devices under test
**should not be correlated**.

On Fri, Apr 1, 2022 at 1:58 AM Bob kb8tq  wrote:

> Hi
>
> If you are trying to evaluate things like accuracy and stability,
> you really can’t do it internally. You need something else to
> compare to. If you want to count number of dac bits of change
> per hour, you certainly can measure that. Just what it means ….
>
> Bob
>
> > On Mar 31, 2022, at 7:15 PM, Hal Murray  wrote:
> >
> >
> > kb...@n1k.org said:
> >> You really can???t compute things like ADEV by observing the device
> against
> >> itself. You need an external / stable reference that is (hopefully)
> much more
> >> accurate than the GPSDO to compare it to.
> >
> > What can I conclude when looking at data collected internally by a GPSDO
> (or
> > NTP)?
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> > ___
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[time-nuts] disciplning natural phenomena

[Lux, Jim]

As I re-read Fleming's "You Only Live Twice" last night, which features 
a geyser that is "regulated" by a valve of some sort I was intrigued by 
this idea:


Can one discipline a geyser to an external source?

a) I assume there's some data somewhere on eruption timing - sure, Old 
Faithful is quite regular, sufficiently that they can say "the next 
eruption will occur at" and people will gather and watch it.  But what's 
the ADEV? As a kid in the early 70s, I didn't think to ask this 
question, and neither Allan nor Leeson seem to mention it in their 
papers from 1966.  There is a lot of variation in timing performance of 
various geysers, though.  Old Faithful *is* regular, and in a place 
where it's watchable.


b) Are periodic geysers actually regulatable ?- From the little I know 
about how they work, I would think the eruption frequency depends on 
things like the water temperature and flow. It's also possible that the 
valve in Fleming's novel is purely fictional, because it serves as part 
of a plot device at the end (much like closing off the safety valve on a 
boiler).


Or, are geysers an example of a chaotic system that is only seemingly 
regular in some sense? That is, it's not like a VCO, with a consistent 
and well defined relation between the control input and the period. 
Changing the control input may change the period in an unpredictable 
way. Some geysers stop working if the surrounding hydrology changes. Or 
is that simply that the Q of the oscillator is so high that it's easy to 
"get out of operating range".  That would be like trying to discipline a 
spurious parasitic oscillation in an amplifier.


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[time-nuts] Re: 32.768Khz Crystal Trimming

[Bernd Neubig]

Hi,

If you do not want to make it a time-nuts style research project, but just
look for a quick fix - here is a rule of thumb:
This kind of crystal usually has a trimming sensitivity of around -10
ppm/pF. This means, if you increase the value of both capacitors on either
side by 2 pF will increase the load capacitance by 1 pF and thus lower the
frequency by  about 10 ppm.
If you need to vary one cap slightly more than the other, (to get a finer
resolution), please use the one at the output side of the on-chip oscillator
stage.
Take care of the start-up margin (safety to get a reliable start-up after
power on). The larger the capacitors, the lower becomes the margin,
sometimes the margin drops rather quickly. Therefore, after having made the
changes, test the start-up behavior by switching on and off several times,
preferably with a slow voltage ramp.

Enjoy the crystal world (as I did for the last 45 years and still doing).

Bernd


-Ursprüngliche Nachricht-
Von: Dan Kemppainen [mailto:d...@irtelemetrics.com] 
Gesendet: Freitag, 1. April 2022 14:47
An: time-nuts@lists.febo.com
Betreff: [time-nuts] 32.768Khz Crystal Trimming

Hi,

I've got a 32.768Khz (USA number format) crystal on a RTCC oscillator of a
small micro, and it's running fast. Around 10 seconds per day or so. 
This is a bit more than an order of magnitude more than the datasheet
states.

The 9 seconds per day error should be a good measurement. The RTCC is
running a 1 second counter, and that's being compared to a 1 second counter
derived by clocking the micro from a 10Mhz EXT clock reference.
This is consistent between multiple copies of the board.

I'm assuming, the C1/C2 load capacitors to ground needs to be higher in
value to trim that oscillator closer to the correct frequency. Is this
correct? Any quick back of the napkin calculations how much additional load
capacitance would be needed?

For Ref, this is the crystal:
https://abracon.com/Resonators/ABS06.pdf
ABS06-32.768KHZ-1-T

Thanks,
Dan


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[time-nuts] Re: 32.768Khz Crystal Trimming

[Mike Millen]

Remember that the load cap value in the data sheet isn't what you fit in 
the circuit.
First deduct the total stray capacitance on the pcb and the IC 
connections, then double the remainder... that's the value you place 
either side of the crystal.


E.g. if the data sheet says 12.5pF and you estimate the strays to be 
2.5pF then you should place a 20pF at each side of the crystal.

(Because the two caps are effectively in series)

Mike - M0MLM

On 01/04/2022 14:01, Bob kb8tq wrote:

Hi

Given the (very normal) lack of information on the crystal,
it becomes a “try it and see” sort of thing. They seem to
want 12.5 pf as the load cap for the first one listed on the
data sheet. How far off of that is your circuit as it sits?

First step would be to take the “output” cap up one value
and see what happens.

Bob


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[time-nuts] Re: 32.768Khz Crystal Trimming

[John Lofgren]

Hi All,

Bob is right.  This is very much a cut-and-try thing for a couple of reasons.
1. Crystals with the same printed specs from different manufacturers respond 
differently.
2. Stray capacitance in the specific installation is part of the total load 
capacitance.  Every installation is different.

I've just run through this on a board for a customer.  It is setup with a 
Microchip RTC that likes crystals with a load capacitance somewhere in the 6 to 
9 pF range.  Using 3 crystals with the same nominal specifications (7 pF, +/- 
20 ppm tolerance) from the different manufacturers I would see frequency errors 
anywhere from -1.6 to -24.5 ppm just by changing the crystal.  On this 
particular board with this particular chip the 7 pF crystal with the lowest 
frequency error liked to have 12 pF load capacitors.  Assuming that the crystal 
actually works best at 7 pF and that the capacitors in the board really are 12 
pF that would make the stray capacitance from the board and in the input/output 
pins of the chip ~1 pF.

The fact that you're seeing an error an order of magnitude off from where it 
should be means something is really mistuned.  I've seen this happen when the 
load capacitance is 2x or 3x off from where it should be.  The attached table 
is something I put together as a quick reference tool for myself to have at the 
bench when trimming capacitors.

If you're interested in digging deeper into the theory there's a pretty 
comprehensive application note from Microchip that might be of interest.

Microchip isn't the only one who publishes this type of application note.  ST 
also has some pretty good oscillator stuff available.

One other thing to note about tuning fork crystals is their temperature 
behavior.  It's terrible (see section 1.7 in the Microchip ap. note).  The 
curve is parabolic with the vertex nominally at 25C.  Once you start getting 
more than a few degrees away from that the slope really starts picking-up.  You 
don't need to get dramatically warmer or colder to start picking-up some 
noticeable time errors in a real-time clock.  These days a lot of the RTC chips 
have internal trim registers to allow the target system to adjust the crystal 
clock cycles per second so the RTC may be disciplined against an external time 
source, if available.

I'm not sure what your application looks like or what test equipment you may 
have available.  Depending on the specific circumstance trimming capacitors may 
be a matter of observing a buffered (possibly pre-scaled) version of the 32.768 
kHz oscillator or measuring the RTC against a known time source.

-John


-Original Message-
From: Bob kb8tq 
Sent: Friday, April 1, 2022 8:01 AM
To: Discussion of precise time and frequency measurement 

Subject: [time-nuts] Re: 32.768Khz Crystal Trimming

EXTERNAL EMAIL: Be careful with attachments and links.

Hi

Given the (very normal) lack of information on the crystal, it becomes a “try 
it and see” sort of thing. They seem to want 12.5 pf as the load cap for the 
first one listed on the data sheet. How far off of that is your circuit as it 
sits?

First step would be to take the “output” cap up one value and see what happens.

Bob

> On Apr 1, 2022, at 8:47 AM, Dan Kemppainen  wrote:
>
> Hi,
>
> I've got a 32.768Khz (USA number format) crystal on a RTCC oscillator of a 
> small micro, and it's running fast. Around 10 seconds per day or so. This is 
> a bit more than an order of magnitude more than the datasheet states.
>
> The 9 seconds per day error should be a good measurement. The RTCC is running 
> a 1 second counter, and that's being compared to a 1 second counter derived 
> by clocking the micro from a 10Mhz EXT clock reference.
> This is consistent between multiple copies of the board.
>
> I'm assuming, the C1/C2 load capacitors to ground needs to be higher in value 
> to trim that oscillator closer to the correct frequency. Is this correct? Any 
> quick back of the napkin calculations how much additional load capacitance 
> would be needed?
>
> For Ref, this is the crystal:
> https://abracon.com/Resonators/ABS06.pdf
> ABS06-32.768KHZ-1-T
>
> Thanks,
> Dan
>
>
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[time-nuts] Re: 32.768Khz Crystal Trimming

[Bob kb8tq]

Hi

Given the (very normal) lack of information on the crystal, 
it becomes a “try it and see” sort of thing. They seem to 
want 12.5 pf as the load cap for the first one listed on the
data sheet. How far off of that is your circuit as it sits?

First step would be to take the “output” cap up one value
and see what happens. 

Bob

> On Apr 1, 2022, at 8:47 AM, Dan Kemppainen  wrote:
> 
> Hi,
> 
> I've got a 32.768Khz (USA number format) crystal on a RTCC oscillator of a 
> small micro, and it's running fast. Around 10 seconds per day or so. This is 
> a bit more than an order of magnitude more than the datasheet states.
> 
> The 9 seconds per day error should be a good measurement. The RTCC is running 
> a 1 second counter, and that's being compared to a 1 second counter derived 
> by clocking the micro from a 10Mhz EXT clock reference.
> This is consistent between multiple copies of the board.
> 
> I'm assuming, the C1/C2 load capacitors to ground needs to be higher in value 
> to trim that oscillator closer to the correct frequency. Is this correct? Any 
> quick back of the napkin calculations how much additional load capacitance 
> would be needed?
> 
> For Ref, this is the crystal:
> https://abracon.com/Resonators/ABS06.pdf
> ABS06-32.768KHZ-1-T
> 
> Thanks,
> Dan
> 
> 
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[time-nuts] 32.768Khz Crystal Trimming

[Dan Kemppainen]

Hi,

I've got a 32.768Khz (USA number format) crystal on a RTCC oscillator of 
a small micro, and it's running fast. Around 10 seconds per day or so. 
This is a bit more than an order of magnitude more than the datasheet 
states.


The 9 seconds per day error should be a good measurement. The RTCC is 
running a 1 second counter, and that's being compared to a 1 second 
counter derived by clocking the micro from a 10Mhz EXT clock reference.

This is consistent between multiple copies of the board.

I'm assuming, the C1/C2 load capacitors to ground needs to be higher in 
value to trim that oscillator closer to the correct frequency. Is this 
correct? Any quick back of the napkin calculations how much additional 
load capacitance would be needed?


For Ref, this is the crystal:
https://abracon.com/Resonators/ABS06.pdf
ABS06-32.768KHZ-1-T

Thanks,
Dan


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[time-nuts] Re: The STM32 GPSDO, a short presentation

[Bob kb8tq]

Hi

The drift used in the original example is just one of many many things
that can come up. There are a lot of “corner cases” in GPSDO design. 
The constellation does “this” and they all react. Ideally they would react
to suppress whatever the issue is. It does not always work out that way.

This is not in any way unique to GPSDO’s. You might have a set of OCXO’s or
Rb’s as the elements in a three corner hat that all had the same tempco slope
and magnitude. In a normal lab, that could create a problem. 

The first time I saw the topic debated it was at FCS. It was in relation to the 
Cs standards used in national time scales ….. ( and why having them all one 
model from one company wasn’t a great idea ). 

Bob

> On Mar 31, 2022, at 10:06 PM, Chris Caudle <6807.ch...@pop.powweb.com> wrote:
> 
> On Thu, March 31, 2022 6:28 pm, Bob kb8tq wrote:
>> Consider the case:
>> 
>> GPS shifts ( possibly due to any of a number of issues).
>> All three modules "move" forward in time by 15 or 20 ns
>> over some time period.
>> The GPSDO's all do their thing and shift frequency by
>> the appropriate amount.
>> 
>> Since all three devices in your three corner hat did the
>> same thing at the same time, all of the delta this / delta
>> that numbers just sit there.
>> They do not show the frequency shift at all.
> 
> That would matter if you wanted to know how good your clock or oscillator
> was (in some sort of absolute sense).
> If all you wanted to know was how good your GPSDO was, wouldn't that
> common mode behavior just fall into an intrinsic aspect of using GPS?
> I think in the case that you want to know how good your particular GPSDO
> is at being a GPS disciplined thing, compare to other models (e.g.
> Thunderbolt, Jackson Labs, HP, etc.) and you can get a good idea of how
> well it performs given the limitations that it has to use GPS to function.
> 
> The bigger problem I see with the original proposal were that there were
> too many of the new design involved, I think three if the model under
> design, and one other homebrew model, so there could be common mode
> problems caused by e.g. a firmware error (frequency offset in a FLL comes
> to mind) that would be hidden by having all the 3 models under test being
> the same.
> By testing e.g. one new model, one Thunderbolt, and one Jackson Labs it
> should at least be possible to tease out what behavior is unique to the
> new STM32 device.
> 
> -- 
> Chris Caudle
> 
> 
> 
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[time-nuts] Re: The STM32 GPSDO, a short presentation

[Hal Murray]

nea...@gmail.com said:
> And, I assume that since we have no idea if the used rubidium oscillator from
> ebay is working properly anymore (aside from output seen on a counter), then
> we should take that rubidium oscillator to a calibration vendor and pay them
> to test it, correct? 

I think an amateur can do a reasonable job of calibrating a rubidium.  I 
wouldn't adjust anything, just measure the actual frequency and use that as a 
correction factor when processing other data.

The idea is to assume it has good long term stability and compare it with GPS 
(which has very very good long term stability).

Do you know about TVB's picDIV and picPET?
  http://www.leapsecond.com/pic/

If you have a scope, use a picDIV to make a PPS from the rubidium.  Compare 
the PPS from GPS with the PPS from the rubidium.  Reset the picDIV until they 
are close together.  They will drift slowly.  Hopefully very slowly.  Come 
back in an hour or day and see how far they have drifted.  Now do the math.  
Repeat.

I have a Rigol scope.  I'm pretty sure I could program it to automate the data 
collection.

If you have a counter/timer that your PC can talk to, measure the time from 
one PPS to the other.


If you have a PC, get a picPET, clock it from the rubidium and watch the PPS 
from a GPS.  The picDIV is only accurate to 400 ns.  You can get a lot better 
than that if you pick your times to match when the picPET shifts across a 
clock edge.

Mumble.  I don't know how to describe that in words that will be easy to 
understand.  It will be obvious after you see it.  Consider reading a clock 
that only ticks once per second, like the typical CMOS clock on a PC.  Assume 
your PC has a clock and you want to know how far off it is.  Spin reading the 
CMOS clock until it changes.  Then grab your PC clock.  That gets you your PC 
clock close to the beginning of a second.

For the picPET, instead of using 2 samples 24 hours apart, adjust the 
start/stop times for your 24 hour run to start right after the picPET 
fraction-within-a-second changes.


For more accuracy, get a TAPR TICC.  $229
  https://tapr.org/product/tapr-ticc/
Thanks John.  You did a wonderful job.


-- 
These are my opinions.  I hate spam.


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[time-nuts] Re: The STM32 GPSDO, a short presentation

[Bob kb8tq]

Hi

The simple answer is to use your three corner hat approach and
use a different source for each of the corners. Possibly a cheap 
Rb for one and a fairly good OCXO for another. Then make your
GPSDO the third corner. 

No, you don’t eliminate all questions this way, but you do address
the common mode problem. 

To properly come up with accurate data then you are into the 
“welcome to Time Nuts” empire of “many sources” that you can 
compare to each other. You can then start sorting the good ones
from the bad ones. 

Yes, you could instead spend a lot of money on a commercial 
standard and just use that. Some do.

Bob

> On Mar 31, 2022, at 8:20 PM, Neal Pollack  wrote:
> 
> So then, I think what I hear you saying, is that if a  person/newbie/time-nut> wants to
> see if a GPSDO that they built, or purchased on ebay, is working OK, then
> they really need to
> purchase a non-GPS rubidium oscillator on ebay, and use that as a ref to
> compare their GPSDO under
> test?
> 
> And, I assume that since we have no idea if the used rubidium oscillator
> from ebay is working properly
> anymore (aside from output seen on a counter), then we should take that
> rubidium oscillator to a
> calibration vendor and pay them to test it, correct?
> 
> Then, we can measure?
> 
> Neal
> 
> 
> On Thu, Mar 31, 2022 at 4:43 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Consider the case:
>> 
>> GPS shifts ( possibly due to any of a number of issues). All three modules
>> “move” forward in time by 15 or 20 ns over some time period.
>> 
>> The GPSDO’s all do their thing and shift frequency by the appropriate
>> amount.
>> 
>> Since all three devices in your three corner hat did the same thing at the
>> same time, all of the delta this / delta that numbers just sit there. They
>> do
>> not show the frequency shift at all.
>> 
>> Yes, it’s a bit of a contrived example, but it is why a common mode issue
>> is going to be a problem.
>> 
>> Bob
>> 
>>> On Mar 31, 2022, at 6:38 PM, André Balsa  wrote:
>>> 
>>> Hi Bob,
>>> I haven't taken a close look at the math behind the Three-Cornered Hat
>>> method yet, but I would imagine there is a mathematical way to remove or
>> at
>>> least quantify the uncertainty ("jitter") introduced by the (separate,
>> but
>>> similar) GPS receivers in the three GPSDOs under test?
>>> 
>>> On Fri, Apr 1, 2022 at 12:02 AM Bob kb8tq  wrote:
>>> 
 Hi
 
 The gotcha of looking at one GPSDO against another is that
 the GPS side of things is “common mode” to all of the devices.
 
 Bob
 
> On Mar 31, 2022, at 4:16 PM, André Balsa  wrote:
> 
> Hi Bob,
> "You need an external / stable reference that is (hopefully) much more
> accurate than the GPSDO to compare it to."
> 
> I fully agree, and of course I don't have an atomic clock at hand. But
>> I
> was thinking that there is an alternative: the Three-Cornered Hat
>> method.
> In any case, we are not there yet, I still have to write the code for
>> tab
> delimited reporting, and then collect the data from the 4 different
 GPSDOs
> I have here (3 x STM32 GPSDO + 1 x Lars' DIY GPSDO), and then setup
> the Three-Cornered Hat measurement apparatus, and then collect more
>> data,
> etc...
> Oh the joys of time-nuttery!
> 
> On Thu, Mar 31, 2022 at 9:01 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> One word of caution:
>> 
>> You really can’t compute things like ADEV by observing the device
 against
>> itself. You need an external / stable reference that is (hopefully)
>> much
>> more
>> accurate than the GPSDO to compare it to.
>> 
>> Bob
>> 
>>> On Mar 31, 2022, at 2:18 PM, André Balsa 
>> wrote:
>>> 
>>> Hello time-nuts,
>>> This is a quick follow-up to my short presentation of the STM32 GPSDO
>>> project, because as some of you noticed, the EEVblog thread is
>>> unfortunately 27 pages long and growing... :(
>>> A few pointers:
>>> 1. If you are interested in the technical details or further
>> understanding
>>> of the project, I suggest reading **only the first post** in the
 EEVblog
>>> thread and then jumping straight to the schematics in post #378, page
 16
>> in
>>> the thread, and then reading the generously commented source code on
>> GitHub
>>> (download the zip file for the latest release and check the GPSDO.ino
>>> sketch).
>>> 2. The core of this project is made of just three components:
>>> a. The STM32F411CEU6 "Black Pill"
>>> b. The 10 MHz OCXO
>>> c. The ublox M8N GPS receiver module
>>> These three components plus a few resistors, capacitors and an LED
>> and
>>> voila!, you have a working GPSDO. Everything else is optional. But of
>>> course the optional parts are where the fun is, really.
>>> 3. Likewise the core of the firmware is just 15 lines of C code,
>> which
>> are
>>> used to setup the 64-bit counter (10