Re: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Bob Camp]

Hi


> On Mar 21, 2017, at 1:07 AM, Chris Albertson  
> wrote:
> 
> I built one of these using a PWM DAC also.   The design was posted to this
> list so I can't take credit for the idea.   But we used two PWM output
> pins.   The PWM provides more voltage range than is needed by the OXO's
> EFC.  To the output was scaled by a voltage divider.  This also scaled down
> thew step size. The second PWN output was scale down even more, like
> maybe 100X more.  The two PWM outputs were added.  One does course
> adjustment the other fine.   The software first sets the course PWM and
> then the fine one takes over.
> 
> But the PWM output was just run through an RC filter with a very long time
> constants low pass filter with corner freq. < 1 Hz.   The goal was to build
> a VERY low cost GPSDO and adding a good external DAC would add to the cost.
> 
> Someone here recently suggested that one could do as well by simply
> adjusting a good oversized crystal with a screw driver as they could using
> a simple GPSDO.   Well, before building the GPSDO I tried keeping my OXO in
> sync with my Tunderbolt using just a screw driver and a dual trace analog
> tektronix scope.  It is REALLY hard to do with a screw driver.

You need a finer adjust pot on the EFC. It’s no different than the process you 
describe above with the PWM’s. With a PPS that is good to 10 ns, you can get
to 0.1 ppb in 1000 seconds with margin. You will have a pretty good idea of 
what is going on in 100 seconds. 

If you are going to rig it up, a 20 turn wire wound pot with a dial on it is 
the high
end approach. Set up the pot with a ~1x10^-8 full scale range. You then have 
roughly 5x10^-10 per turn. The cool part is that you can log the readings and
work out what’s going on with the OCXO.

Bob

>   Some tines
> I'd think I had it right then I'd look at the scope after 30 minutes and
> fine one sine wave had gained 1/4 cycle on the other.  Lots of reason for
> this, perhaps one of my voltage regulators are temperature sensitive,
> "stiction" in the screw I was turning.  Who knows. But my simple GPSDO
> would notice the 1/4 cycle error and fix it automatically
> 
> It real life for practical purposes I use the Rb clock, was lucky to get
> one at the old $35 price.
> 
> On Mon, Mar 20, 2017 at 4:43 PM, Mark Sims  wrote:
> 
>> The "DAC" was PWM based, but used a separate voltage regulator for the
>> "reference".  I never tried it using the USB power as the reference.
>> 
>> The OCXO (+board) uses less than 500 mA warming up (which it does rather
>> quickly).  It's in a small hermetic package about twice the size of a
>> standard DIP-14 oscillator package.  There was a Ebay seller several years
>> ago offering them at $15 each or 10 for $100.
>> 
>> The Chinese "Arduino" board (it's not really and Arduino,  just a MEGA 328
>> and a proto area)  has a micro-USB connector for power input but does not
>> implement USB data.   I used the processor serial port with a level shifter
>> dongle.   The firmware was a cheap and dirty hack and I didn't implement
>> much in the way of control or monitoring... never got around to improving
>> it.  The project was basically "Hey, I forgot I had those parts...  Hmmm,
>> one could build a simple GPSDO... why not?
>> 
>> -
>> 
>>> Did you use the Arduino's PWM output plus a LPF for the DAC, or a
>> separate
>> DAC? If PWM, did you have problems with noise or sensitivity to the
>> USB-provided supply voltage?
>> ___
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>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Chris Albertson]

I built one of these using a PWM DAC also.   The design was posted to this
list so I can't take credit for the idea.   But we used two PWM output
pins.   The PWM provides more voltage range than is needed by the OXO's
EFC.  To the output was scaled by a voltage divider.  This also scaled down
thew step size. The second PWN output was scale down even more, like
maybe 100X more.  The two PWM outputs were added.  One does course
adjustment the other fine.   The software first sets the course PWM and
then the fine one takes over.

But the PWM output was just run through an RC filter with a very long time
constants low pass filter with corner freq. < 1 Hz.   The goal was to build
a VERY low cost GPSDO and adding a good external DAC would add to the cost.

Someone here recently suggested that one could do as well by simply
adjusting a good oversized crystal with a screw driver as they could using
a simple GPSDO.   Well, before building the GPSDO I tried keeping my OXO in
sync with my Tunderbolt using just a screw driver and a dual trace analog
tektronix scope.  It is REALLY hard to do with a screw driver.   Some tines
I'd think I had it right then I'd look at the scope after 30 minutes and
fine one sine wave had gained 1/4 cycle on the other.  Lots of reason for
this, perhaps one of my voltage regulators are temperature sensitive,
"stiction" in the screw I was turning.  Who knows. But my simple GPSDO
would notice the 1/4 cycle error and fix it automatically

It real life for practical purposes I use the Rb clock, was lucky to get
one at the old $35 price.

On Mon, Mar 20, 2017 at 4:43 PM, Mark Sims  wrote:

> The "DAC" was PWM based, but used a separate voltage regulator for the
> "reference".  I never tried it using the USB power as the reference.
>
> The OCXO (+board) uses less than 500 mA warming up (which it does rather
> quickly).  It's in a small hermetic package about twice the size of a
> standard DIP-14 oscillator package.  There was a Ebay seller several years
> ago offering them at $15 each or 10 for $100.
>
> The Chinese "Arduino" board (it's not really and Arduino,  just a MEGA 328
> and a proto area)  has a micro-USB connector for power input but does not
> implement USB data.   I used the processor serial port with a level shifter
> dongle.   The firmware was a cheap and dirty hack and I didn't implement
> much in the way of control or monitoring... never got around to improving
> it.  The project was basically "Hey, I forgot I had those parts...  Hmmm,
> one could build a simple GPSDO... why not?
>
> -
>
> > Did you use the Arduino's PWM output plus a LPF for the DAC, or a
> separate
> DAC? If PWM, did you have problems with noise or sensitivity to the
> USB-provided supply voltage?
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California
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[time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Mark Sims]

The "DAC" was PWM based, but used a separate voltage regulator for the 
"reference".  I never tried it using the USB power as the reference.

The OCXO (+board) uses less than 500 mA warming up (which it does rather 
quickly).  It's in a small hermetic package about twice the size of a standard 
DIP-14 oscillator package.  There was a Ebay seller several years ago offering 
them at $15 each or 10 for $100.

The Chinese "Arduino" board (it's not really and Arduino,  just a MEGA 328 and 
a proto area)  has a micro-USB connector for power input but does not implement 
USB data.   I used the processor serial port with a level shifter dongle.   The 
firmware was a cheap and dirty hack and I didn't implement  much in the way of 
control or monitoring... never got around to improving it.  The project was 
basically "Hey, I forgot I had those parts...  Hmmm, one could build a simple 
GPSDO... why not?

-

> Did you use the Arduino's PWM output plus a LPF for the DAC, or a separate
DAC? If PWM, did you have problems with noise or sensitivity to the
USB-provided supply voltage?
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Re: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Attila Kinali]

Moin,

On Mon, 20 Mar 2017 17:11:36 -0400
"William H. Fite"  wrote:

> You are talking about product design, development and optimization, not the
> production of a one-off for home use. Since performance standards are
> already well established, it is only necessary for the developer to test
> the bench built instrument against published standards and determine if
> performance is good enough to suit him. Given a sound understanding of the
> role of various components in the system, it will be a great deal faster
> and easier for the builder to tinker with the one-off then to go through an
> extensive process of model development and verification.
> 
> I have spent a good deal of my career doing performance modeling,
> verification, and validation in collaboration with other scientists and
> also engineers. You describe the process correctly but I think it is
> generous overkill for the topic under discussion here. Or have I missed
> something in the discussion? Is the desired end result a device for
> manufacture and sale? If so, then your approach is right on target.

The question kind of started of from how to verify a GPSDO works correctly.
My answer to that was to use a known-good GPSDO and an vapor cell Rb standard.
Both can be had for quite cheap (<200$ each) or borrowed from a fellow
time-nut. With this and a suitable counter (e.g. PICTIC or TICC) one can
verify the homebew GPSDO quickly and quantify the result.

Chris Albertson injected, that he wanted to do the verification with stuff
he could build on his own, not relying on another GPSDO or "expensive" Rb
standard. I then showed that, while possible to do so, it takes a lot of
effort and time to verify instruments without using known-good references.

Yes, you are right that for Joe Average, this is way overkill. For most
it will be enough to check whether the GPSDO is within 10-20ns of another
GPS (without DO) receiver, and whether the EFC correlates well with the
temperature of the OCXO housing. Both checks can be done relatively quickly,
given access to a counter, a precise thermometer, and a DMM.

But then, this is time-nuts. We love to get the best out of a specific
system... even if it takes more effort than just simply buying better
equipment :-)


Attila Kinali
-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Jim Harman]

On Mon, Mar 20, 2017 at 4:14 PM, Mark Sims  wrote:

> $3 for an  Arduino chip on a PCB with proto area from China (should have
> bought a lot more when they were available),$10 for a small ovenized 5V
> TTL output OCXO (also should have bought a lot more),  and $5 for misc
> parts (OK, beer money not included in the BOM).   Batteries not needed,
> powered off USB.


Hi Mark,

Did you use the Arduino's PWM output plus a LPF for the DAC, or a separate
DAC? If PWM, did you have problems with noise or sensitivity to the
USB-provided supply voltage?

Also I have found that not all computer USB ports can supply enough warm-up
current for a 5V OCXO. Or did you use a hefty USB charger and miss out on
the ability to get logging info back over the USB port?




-- 

--Jim Harman
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[time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[William H. Fite]

Attilla,

You are talking about product design, development and optimization, not the
production of a one-off for home use. Since performance standards are
already well established, it is only necessary for the developer to test
the bench built instrument against published standards and determine if
performance is good enough to suit him. Given a sound understanding of the
role of various components in the system, it will be a great deal faster
and easier for the builder to tinker with the one-off then to go through an
extensive process of model development and verification.

I have spent a good deal of my career doing performance modeling,
verification, and validation in collaboration with other scientists and
also engineers. You describe the process correctly but I think it is
generous overkill for the topic under discussion here. Or have I missed
something in the discussion? Is the desired end result a device for
manufacture and sale? If so, then your approach is right on target.

Bill


On Monday, March 20, 2017, Attila Kinali > wrote:

> On Thu, 16 Mar 2017 00:06:49 -0700
> Chris Albertson  wrote:
>
> > I actually did use your method.  I have a Rb and Thunderbolt, a pair
> > of freq. counters and so on.But still I wanted to see if I could
> > build from scratch and verify proper operation and keep the budget
> > under say $50 for everything from antenna to power cord. I think
> > it can be done but one can only verify longer term stability.
>
> Hmm.. doing verification of self-built (or aquired) equipment from
> scratch is a different game altogether. If you want to build things
> yourself, you first have to form a model of what disturbs your system,
> measure these parameters and verify the model against your measurements.
> Then you start building systems that exhibit different distortions,
> model these, measure and verify them. After you have built enough
> systems with different environmental characteristics, you verify
> them against eachother to make sure that your models faithully
> model reality and contain all parameters up to the error bound of the
> model.
>
> After a couple of decades of building and verification, you can be
> reasonably sure your GPSDO works correctly ;-)
>
>
> > (Yes you were correct a GOOD oversized XO is not sensitive to the
> > environment.  But notice the above budget.)
>
> 50$ for a complete GPSDO, batteries included, is quite a low price limit.
> A decent OCXO already costs 20-30$ on ebay. 100-200$ is a more realistic
> limit for a homebrew GPSDO with time-nuts like performance.
> A non-ovenized XO will not come close to time-nuts standards ;-)
>
>
> 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
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/m
> ailman/listinfo/time-nuts
> and follow the instructions there.
>


-- 
William H Fite, PhD
Independent Consultant
Statistical Analysis & Research Methods
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[time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Mark Sims]

I did it for $25...  $7 for the GPS+antenna module,  $3 for an  Arduino chip on 
a PCB with proto area from China (should have bought a lot more when they were 
available),$10 for a small ovenized 5V TTL output OCXO (also should have 
bought a lot more),  and $5 for misc parts (OK, beer money not included in the 
BOM).   Batteries not needed, powered off USB.   It worked better than I 
expected... not Tbolt quality, but not too shabby for a thee-day weekend hack.  
   $50 (and a lot of work)  is certainly doable for a decent home-brew GPSDO.

---

> 50$ for a complete GPSDO, batteries included, is quite a low price limit.
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Re: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Bob Stewart]

I would say that the price for a home-built time-nuts quality GPSDO is going to 
be significantly greater than $200.  Yes, if you are making them for sale, 
eventually the unit cost will get down there.  But to build one single good 
GPSDO, you're going to throw away a lot of prototypes on the way to the one 
that works well enough to stand up to the scrutiny of this group.  The costs of 
those prototypes add up, and then there's your time engineering, building and 
testing.  It adds up to a lot.

Bob 




  From: Attila Kinali <att...@kinali.ch>
 To: Discussion of precise time and frequency measurement <time-nuts@febo.com> 
 Sent: Monday, March 20, 2017 2:01 PM
 Subject: [time-nuts] time-nuts equipment verification from scratch (was: WTB: 
GPSDO)
   
On Thu, 16 Mar 2017 00:06:49 -0700
Chris Albertson <albertson.ch...@gmail.com> wrote:

> I actually did use your method.  I have a Rb and Thunderbolt, a pair
> of freq. counters and so on.    But still I wanted to see if I could
> build from scratch and verify proper operation and keep the budget
> under say $50 for everything from antenna to power cord.    I think
> it can be done but one can only verify longer term stability.

Hmm.. doing verification of self-built (or aquired) equipment from
scratch is a different game altogether. If you want to build things
yourself, you first have to form a model of what disturbs your system,
measure these parameters and verify the model against your measurements.
Then you start building systems that exhibit different distortions,
model these, measure and verify them. After you have built enough
systems with different environmental characteristics, you verify
them against eachother to make sure that your models faithully
model reality and contain all parameters up to the error bound of the model.

After a couple of decades of building and verification, you can be 
reasonably sure your GPSDO works correctly ;-)


> (Yes you were correct a GOOD oversized XO is not sensitive to the
> environment.  But notice the above budget.)

50$ for a complete GPSDO, batteries included, is quite a low price limit.
A decent OCXO already costs 20-30$ on ebay. 100-200$ is a more realistic
limit for a homebrew GPSDO with time-nuts like performance.
A non-ovenized XO will not come close to time-nuts standards ;-)


                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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[time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

[Attila Kinali]

On Thu, 16 Mar 2017 00:06:49 -0700
Chris Albertson  wrote:

> I actually did use your method.  I have a Rb and Thunderbolt, a pair
> of freq. counters and so on.But still I wanted to see if I could
> build from scratch and verify proper operation and keep the budget
> under say $50 for everything from antenna to power cord. I think
> it can be done but one can only verify longer term stability.

Hmm.. doing verification of self-built (or aquired) equipment from
scratch is a different game altogether. If you want to build things
yourself, you first have to form a model of what disturbs your system,
measure these parameters and verify the model against your measurements.
Then you start building systems that exhibit different distortions,
model these, measure and verify them. After you have built enough
systems with different environmental characteristics, you verify
them against eachother to make sure that your models faithully
model reality and contain all parameters up to the error bound of the model.

After a couple of decades of building and verification, you can be 
reasonably sure your GPSDO works correctly ;-)


> (Yes you were correct a GOOD oversized XO is not sensitive to the
> environment.  But notice the above budget.)

50$ for a complete GPSDO, batteries included, is quite a low price limit.
A decent OCXO already costs 20-30$ on ebay. 100-200$ is a more realistic
limit for a homebrew GPSDO with time-nuts like performance.
A non-ovenized XO will not come close to time-nuts standards ;-)


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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