Re: [time-nuts] NCOCXO anyone?

[Alex Pummer]

it is a way to use a carrier fc to make one SSB  signal with fm 
modulation frequency, use just the side-band, , which have a frequency 
of fc + fm = fR,  [fR/fc is a function of the SSB modulator carrier 
suppression capability,]  fm could be from less than 1/2 fc any 
frequency to zero, if it is zero fR =f c. With fm is not zero, the phase 
of fR will advance relative to  fc as long as fm is not zero if fm 
becomes zero the advance will stop.
The generation of a very small frequency offset will need fm = the 
offset frequency
To "clean up" the resulting fR, a PLL could be locked to it, which could 
look to one single frequency only [with very narrow tuning range 
oscillator, perhaps a a tunable crystal and very narrow loop filter 
[just to let pass fm ]
since oscillators are by definition amplifiers with infinite high gain 
that PLL could look  into fc!
Attila I don't know anything about any patent, but I developed that kind 
of system for video colour performance analyzing system in the "past 
century".

73
KJ6UHN
Alex

On 7/29/2016 9:23 AM, Attila Kinali wrote:

On Fri, 29 Jul 2016 00:26:07 + (UTC)
Bruce Griffiths  wrote:


Diophantine Frequency Synthesizer Design for Timekeeping Systems

I quickly went over the papers people have pointed me at. Without
having gone through all the math, the idea for choosing the PLL values
looks neat. The 2-cascaded synthesizer is also the one used by Spectratime
for their FemtoStepper, which bring us back to the question: How do they
achieve phase steps? I see how offset frequencies are generated (with
arbitrary small step sized), but I do not see how this can be turned
in fine resulution phase steps when using PLL's as the controlling elements.


Discusses a diophantine synthesiser.Note Sotiriadis' work on diophantine
numbers and frequency synthesis appears to be a rehash of an old Patent
perhaps due to a lack of competent searching for prior art.This issue was
discussed on the list some time ago,

Which patent are you refering to?

Attila Kinali


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Re: [time-nuts] NCOCXO anyone?

[Attila Kinali]

On Fri, 29 Jul 2016 00:26:07 + (UTC)
Bruce Griffiths  wrote:

> Diophantine Frequency Synthesizer Design for Timekeeping Systems

I quickly went over the papers people have pointed me at. Without
having gone through all the math, the idea for choosing the PLL values
looks neat. The 2-cascaded synthesizer is also the one used by Spectratime
for their FemtoStepper, which bring us back to the question: How do they
achieve phase steps? I see how offset frequencies are generated (with
arbitrary small step sized), but I do not see how this can be turned
in fine resulution phase steps when using PLL's as the controlling elements.

> Discusses a diophantine synthesiser.Note Sotiriadis' work on diophantine
> numbers and frequency synthesis appears to be a rehash of an old Patent
> perhaps due to a lack of competent searching for prior art.This issue was
> discussed on the list some time ago,

Which patent are you refering to?

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] NCOCXO anyone?

[Bruce Griffiths]

Diophantine Frequency Synthesizer Design for Timekeeping Systems
|   |
|   |  |   |   |   |   |   |
| Diophantine Frequency Synthesizer Design for Timekeepi...Abstract Diophantine 
Frequency Synthesis (DFS), a number-theoretic approach to the design of very 
high resolution frequency synthesizers, was introduced in 2006.  |
|  |
| View on www.hindawi.com | Preview by Yahoo |
|  |
|   |




Discusses a diophantine synthesiser.Note Sotiriadis' work on diophantine 
numbers and frequency synthesis appears to be a rehash of an old Patent perhaps 
due to a lack of competent searching for prior art.This issue was discussed on 
the list some time ago,
Bruce
 

On Friday, 29 July 2016 6:31 AM, Attila Kinali  wrote:
 

 On Fri, 22 Jul 2016 08:19:43 + (UTC)
Bruce Griffiths  wrote:

> No, the first one merely uses a pair of cascaded heterodyne PLLs
> as shown on p3 of the manual.

Ok. I tried to understand how this circuit works. While I can see
how a small and precise frequency offset can be produced, I do not
see how a small phase offset with fixed frequency can be produced.
At least not at the 100fs resolution level they are claiming in
the manual. Would someone be so kind and explain the working
of the circuit?

> A diophantine setup may be useful here if one wished to construct something 
> similar.

What is a diophantine setup?


                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] NCOCXO anyone?

[Attila Kinali]

On Thu, 28 Jul 2016 14:06:09 -0700
Alex Pummer  wrote:

> On 7/28/2016 11:03 AM, Attila Kinali wrote:
> > On Fri, 22 Jul 2016 08:19:43 + (UTC)
> > Bruce Griffiths  wrote:
> >
> >> No, the first one merely uses a pair of cascaded heterodyne PLLs
> >> as shown on p3 of the manual.
> > Ok. I tried to understand how this circuit works. While I can see
> > how a small and precise frequency offset can be produced, I do not
> > see how a small phase offset with fixed frequency can be produced.
> > At least not at the 100fs resolution level they are claiming in
> > the manual. Would someone be so kind and explain the working
> > of the circuit?

> if you send the circuit to me Attila, I would try to help you

Ah.. sorry. the link got cut off when i trimmed the mail.
It's the one on page three in the FemtoStepper manual:
http://www.spectratime.com/products/itest/clock-instruments/FemtoStepper/


Attila Kinali

-- 
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Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] NCOCXO anyone?

[Alex Pummer]

if you send the circuit to me Attila, I would try to help you

73
KJ6UHN
Alex
by the way aside of that ham license, I have some fifty years of 
experience and also an MSEE


On 7/28/2016 11:03 AM, Attila Kinali wrote:

On Fri, 22 Jul 2016 08:19:43 + (UTC)
Bruce Griffiths  wrote:


No, the first one merely uses a pair of cascaded heterodyne PLLs
as shown on p3 of the manual.

Ok. I tried to understand how this circuit works. While I can see
how a small and precise frequency offset can be produced, I do not
see how a small phase offset with fixed frequency can be produced.
At least not at the 100fs resolution level they are claiming in
the manual. Would someone be so kind and explain the working
of the circuit?


A diophantine setup may be useful here if one wished to construct something 
similar.

What is a diophantine setup?


Attila Kinali



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Re: [time-nuts] NCOCXO anyone?

[Attila Kinali]

On Fri, 22 Jul 2016 08:19:43 + (UTC)
Bruce Griffiths  wrote:

> No, the first one merely uses a pair of cascaded heterodyne PLLs
> as shown on p3 of the manual.

Ok. I tried to understand how this circuit works. While I can see
how a small and precise frequency offset can be produced, I do not
see how a small phase offset with fixed frequency can be produced.
At least not at the 100fs resolution level they are claiming in
the manual. Would someone be so kind and explain the working
of the circuit?

> A diophantine setup may be useful here if one wished to construct something 
> similar.

What is a diophantine setup?


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] NCOCXO anyone?

[Bob Camp]

Hi

A typical double oven design runs about 10 mw or so in the circuitry 
in the inner oven. The “stuff” inside the outer oven likely doubles that 
number. 
The rest of the circuit is put outside the outer oven to reduce heat rise. There
could be another 40 mw in that part of the circuit. Everything else is 
controlled 
power to heat things and will go to zero at the highest temperature. 

If you run the inner oven at an offset of 3 to 5 C from the outer, the inner
heater will likely not pull more than 40 mw and may pull quite a bit less.

Bob


> On Jul 24, 2016, at 4:45 PM, James Flynn  wrote:
> 
> Richard (Rick) Karlquist  writes:
> 
> 
>> The last thing you want in an oven is a lot of
>> added thermal overhead, especially in a double oven
>> where you already fighting against running out of
>> temperature range.  If you want to ovenize everything
>> but the kitchen sink, put it in it's own oven that is
>> separate from the crystal oven.
> 
> The thermal overhead is quite small compared to the power required for 
> the outer oven to hold temperature.  80mW maximum as opposed to about 1 
> watt.
> 
> I did a comparison of the temperature rise of running the unit 
> essentially as a single, inner oven with the rest of the electronics 
> mentioned in the outer "box", and then turning on the outer heater.  The 
> Q from the inner oven was far and away the dominant factor.
> 
> Putting the DAC inside the outer oven was the obvious solution for me, 
> as opposed to putting them outside in ambient.  I did consider thermal 
> compensation, but again the outer oven would be able to keep things 
> within a fraction of a degree over the range of normal ambient in the 
> lab. 
> 
> Separate ovens seems to be inviting noise getting into the signal lines 
> between the two ovens.  
> 
>> 
>> I also don't like intermingling digital signals with the
>> analog oscillator signal.
> 
> Not sure what you mean by "intermingling". There are separate ground 
> returns for the oscillator output (transformer isolated) and the digital 
> signals. There is a low pass filter between DAC and oscillator control 
> to minimize noise getting across. Also digital circuits and oscillator 
> have their own individual precision regulators.
> 
>> 
>> Have you measured the thermal gain of your outer oven?
>> I suspect it's not much.  You could use inner oven
>> current draw as a proxy.
> 
> I did a while ago and remember it was on the order of 50 - 100. But I 
> have changed the design somewhat and should do it again when the 
> experiment gets going.
> 
> 
> 
> 
> 
> 
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Re: [time-nuts] NCOCXO anyone?

[Hal Murray]

> 24 bit DAC

Which chip are you using?  How many useful bits do you think you will get?


-- 
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Re: [time-nuts] NCOCXO anyone?

[James Flynn]

Richard (Rick) Karlquist  writes:


> The last thing you want in an oven is a lot of
> added thermal overhead, especially in a double oven
> where you already fighting against running out of
> temperature range.  If you want to ovenize everything
> but the kitchen sink, put it in it's own oven that is
> separate from the crystal oven.

The thermal overhead is quite small compared to the power required for 
the outer oven to hold temperature.  80mW maximum as opposed to about 1 
watt.

I did a comparison of the temperature rise of running the unit 
essentially as a single, inner oven with the rest of the electronics 
mentioned in the outer "box", and then turning on the outer heater.  The 
Q from the inner oven was far and away the dominant factor.

Putting the DAC inside the outer oven was the obvious solution for me, 
as opposed to putting them outside in ambient.  I did consider thermal 
compensation, but again the outer oven would be able to keep things 
within a fraction of a degree over the range of normal ambient in the 
lab. 

Separate ovens seems to be inviting noise getting into the signal lines 
between the two ovens.  

> 
> I also don't like intermingling digital signals with the
> analog oscillator signal.

Not sure what you mean by "intermingling". There are separate ground 
returns for the oscillator output (transformer isolated) and the digital 
signals. There is a low pass filter between DAC and oscillator control 
to minimize noise getting across. Also digital circuits and oscillator 
have their own individual precision regulators.

> 
> Have you measured the thermal gain of your outer oven?
> I suspect it's not much.  You could use inner oven
> current draw as a proxy.

I did a while ago and remember it was on the order of 50 - 100. But I 
have changed the design somewhat and should do it again when the 
experiment gets going.






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Re: [time-nuts] NCOCXO anyone?

[Richard (Rick) Karlquist]

On 7/24/2016 6:44 AM, James Flynn wrote:

Hal Murray  writes:

Has anybody put the DAC and all of the analog stuff inside the oven?

Seems

like an obvious idea so somebody has probably patented it.



I am using a 5 MHz custom built design which has everything inside the
outer oven in a double oven.

This includes:

Precision regulators for DC supply.
24 bit DAC
Reference for DAC
All analog devices, resistors and capacitors after DAC.
All buffer amplifiers from oscillator.

Unit only has raw DC and I2C lines for inputs and 5MHz sine wave out at
3 volts p-p.

It also seemed the obvious way to go in the design.


IMHO, it isn't obvious that this is the way to go.
Nor is it a "free lunch" as it seems to be envisioned.
The last thing you want in an oven is a lot of
added thermal overhead, especially in a double oven
where you already fighting against running out of
temperature range.  If you want to ovenize everything
but the kitchen sink, put it in it's own oven that is
separate from the crystal oven.

I also don't like intermingling digital signals with the
analog oscillator signal.

Have you measured the thermal gain of your outer oven?
I suspect it's not much.  You could use inner oven
current draw as a proxy.

Rick
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Re: [time-nuts] NCOCXO anyone?

[James Flynn]

Hal Murray  writes:


> That still leaves the temperature quirks of the DAC and amplifiers.
> 
> Has anybody put the DAC and all of the analog stuff inside the oven?  
Seems 
> like an obvious idea so somebody has probably patented it.
> 

I am using a 5 MHz custom built design which has everything inside the 
outer oven in a double oven.

This includes:

Precision regulators for DC supply.
24 bit DAC
Reference for DAC
All analog devices, resistors and capacitors after DAC.
All buffer amplifiers from oscillator.

Unit only has raw DC and I2C lines for inputs and 5MHz sine wave out at 
3 volts p-p. 

It also seemed the obvious way to go in the design.  

Performance is difficult to measure with equipment on hand.  Waiting on 
funding for experiment which includes equipment traceable to NIST.
 



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Re: [time-nuts] NCOCXO anyone?

[Charles Steinmetz]

Hal wrote:


There are 2 markets for DACs and ADCs.  I'll call them DC and RF, but the RF
goes down to audio.

In the DC market, the data sheet talks about linearity and usually covers
temperature stability.
* * *
In the RF market, nobody cares about temperature drift.


By far the largest market for 16+ bit converters (both ADC and DAC) is 
digital audio.  Virtually all current audio converters use sigma-delta 
("one-bit") conversion with huge oversampling rates.  For a variety of 
reasons, these are quite well suited to the requirements of digital 
audio, but they all have serious shortcomings WRT DC performance, 
tempco, absolute accuracy, and the dreaded idle tones (Google for more 
than you could read in a lifetime).


Fortunately, the sheer volume of this market means that you can get 
really excellent audio (and audio-like) performance for very reasonable 
cost.  Unfortunately, it tempts designers to misuse the inexpensive 
audio chips for general DAQ tasks (for example, the many glorified, 
DC-coupled,  "DAQ" PC sound cards and "instrument on a board" products 
available today).


Best regards,

Charles


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Re: [time-nuts] NCOCXO anyone?

[Chris Caudle]

On Fri, July 22, 2016 2:15 pm, Hal Murray wrote:
> Has anybody put the DAC and all of the analog stuff inside the oven?

I ran across some OCXO's with a DAC inside the oven a few years back. 
They were 5MHz instead of the 10MHz I was looking for so I didn't buy them
at the time.  I have forgotten the vendor, but I seem to recall they had a
Maxim DAC inside the oven.

-- 
Chris Caudle


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Re: [time-nuts] NCOCXO anyone?

[Hal Murray]

att...@kinali.ch said:
> You can already get 24bit DAC's off the shelf from TI (DAC1282). I do not
> know how stable they are in reality. ...

There are 2 markets for DACs and ADCs.  I'll call them DC and RF, but the RF 
goes down to audio.

In the DC market, the data sheet talks about linearity and usually covers 
temperature stability.

In the RF market, the data sheet has Fourier transform plots when the input 
is a clean sine wave or pair of sine waves.   Think software radios, radar or 
spread spectrum.  The usual one term summary is ENOB: Effective Number of 
Bits.

In the RF market, nobody cares about temperature drift.


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Re: [time-nuts] NCOCXO anyone?

[Hal Murray]

rich...@karlquist.com said:
> That's what we tried to do with the E1938A.  A multiplying DAC is used based
> on a reference that is ovenized instead the crystal oven.  That certainly
> eliminated the tempco issue with the reference, but then we discovered 1/f
> noise on the reference.  We had to redesign with a different reference. 

That still leaves the temperature quirks of the DAC and amplifiers.

Has anybody put the DAC and all of the analog stuff inside the oven?  Seems 
like an obvious idea so somebody has probably patented it.


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Re: [time-nuts] NCOCXO anyone?

[Poul-Henning Kamp]

In message <20160722113312.f1f292c42ba086aafd6d4...@kinali.ch>, Attila Kinali w
rites:

>You can already get 24bit DAC's off the shelf from TI (DAC1282).

Precisely(!) as stable as the voltage reference you feed them.

These are oversampling designs which *by definition* cannot attenuate
Vref noise.

-- 
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] NCOCXO anyone?

[Richard (Rick) Karlquist]

On 7/22/2016 10:15 AM, David wrote:



It is too bad voltage control of an oscillator cannot be made
ratiometric.  Or can it?  I have never heard of such a thing.  That
would remove some of the demands on a low drift reference.



That's what we tried to do with the E1938A.  A multiplying DAC
is used based on a reference that is ovenized instead the
crystal oven.  That certainly eliminated the tempco issue
with the reference, but then we discovered 1/f noise on the
reference.  We had to redesign with a different reference.

Rick
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Re: [time-nuts] NCOCXO anyone?

[David]

On Fri, 22 Jul 2016 11:33:12 +0200, you wrote:

>On Thu, 21 Jul 2016 22:22:14 -0500
>David  wrote:
>
>> Increased integration has only helped insofar as you can attempt
>> designs which would have been prohibitive before.
>> 
>> I keep trying to come up with a charge balancing design but what about
>> Linear Technology's solution from back in 2001?
>> 
>> A Standards Lab Grade 20-Bit DAC with 0.1ppm/°C Drift
>> http://www.linear.com/docs/4177
>
>You can already get 24bit DAC's off the shelf from TI (DAC1282).
>I do not know how stable they are in reality.

There are a lot of DACs like the TI DAC1282 which are not primarily
intended for DC applications.  At least according to its
specifications, it's gain error drift is 100 times greater and its
offset error drift is 150 times greater than the LTC2400 ADC used for
discipline in the Linear Technology application note.  The best DC
DACs I could quickly find are only 4 time better than that so still
more than an order of magnitude below the performance of ADCs.

>I looked into high
>precision DAC's a year or two ago and figured out that once you
>cross the 20bit line, all kind of weird stuff happens that is
>hard or almost impossible to compensate for. The trick with using
>an ADC (which are available up to 32bit) doesn't really work either,
>as offset drifts, thermal voltage etc are hard to impossible to
>compensate completely. If you go through the volt-nuts mailinglist,
>you'll see how much effort it is to even keep 1ppm (~20bit) stability
>of a voltage reference... and then to get that performance out of a DAC.

If you expect analog specifications in line with the claimed digital
resolution of ADCs and DACs, you will be disappointed.  20 bits is
about where they top out no matter how many bits are available; the
best you can hope for is that they are monotonic but how meaningful is
that when it is buried in noise?

The LTC2400 is considered suitable for 6 digit designs before software
calibration is used which the application note and datasheet mention.
In this case, it is its repeatable INL which can be corrected for and
its low gain and offset drift which matter.

It is too bad voltage control of an oscillator cannot be made
ratiometric.  Or can it?  I have never heard of such a thing.  That
would remove some of the demands on a low drift reference.

>If anything, I think the better approach is to use high resolution DAC
>like the DAC1282 or maybe the DAC1280 with a custom modulator and put
>it inside the control loop such that the real measurement happens in
>the frequency/time domain. The results from Sherman & Jördens[1]
>seems to indicate that sub-100fs stability should be possible, though
>there are a couple of open questions there.
>
>   Attila Kinali
>
>[1] "Oscillator metrology with software defined radio",
>by Jeff Sherman and Robert Jördens, 2016
>http://dx.doi.org/10.1063/1.4950898
>(it's available from NIST as well)

Based on Rick's description of the problem, it seemed like that was
what HP tried and it did not work because the DAC had too much drift
to compensate for in the frequency/time domain:

>20 years ago when HP was working on a so called "smart clock"
>GPS box, they decided to do what you said, use a DAC to
>tune the EFC on the E1938A oscillator.  I
>recommended to them NOT to try to do that, but they
>didn't listen to me.  At that time, it
>was nearly impossible to come up with a DAC, buffer
>amplifier, and voltage reference that didn't degrade
>the stability of the E1938A, which isn't even as stable
>as a 10811.  What you need to ask yourself is:  in
>2016, can I finally get analog components that are
>an order of magnitude or two better than what was
>available in 1996?  I don't know, without researching
>it.  Certainly, we can't depend on Moore's law coming
>to the rescue.  If anything, that works against analog
>IC's by obsoleting older analog processes.
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Re: [time-nuts] NCOCXO anyone?

[Scott Stobbe]

Capacitor matching (Moore's law) has improved for switch-cap designs.

Also depends on the tuning gain, 10 ppm/V would be very demanding versus 10
ppb/V.

On Thu, Jul 21, 2016 at 9:47 PM, Richard (Rick) Karlquist <
rich...@karlquist.com> wrote:

>
>
> On 7/21/2016 4:56 PM, Nick Sayer via time-nuts wrote:
>
>> Oh my. That’s a bit more than I was originally considering… What I had in
>> mind was adding a DAC front end to an OCXO so that you could tune the EFC
>> with serial commands rather than analog and calling that a product.
>>
>>
> 20 years ago when HP was working on a so called "smart clock"
> GPS box, they decided to do what you said, use a DAC to
> tune the EFC on the E1938A oscillator.  I
> recommended to them NOT to try to do that, but they
> didn't listen to me.  At that time, it
> was nearly impossible to come up with a DAC, buffer
> amplifier, and voltage reference that didn't degrade
> the stability of the E1938A, which isn't even as stable
> as a 10811.  What you need to ask yourself is:  in
> 2016, can I finally get analog components that are
> an order of magnitude or two better than what was
> available in 1996?  I don't know, without researching
> it.  Certainly, we can't depend on Moore's law coming
> to the rescue.  If anything, that works against analog
> IC's by obsoleting older analog processes.
>
> Also in 1996, phase microsteppers were already legacy
> technology and didn't have a good reputation for spectral
> purity.  Another non-panacea.
>
> Rick
>
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Re: [time-nuts] NCOCXO anyone?

[Ole Petter Rønningen]

SpectraDynamics HROG 5/10

http://www.spectradynamics.com/products/hrog-10-high-resolution-phase-and-frequency-offset-generator/

On 22. jul. 2016, at 09.49, Anders Wallin  wrote:

>> rich...@karlquist.com said:
>>> Also in 1996, phase microsteppers were already legacy technology and
>> didn't
>>> have a good reputation for spectral purity.  Another non-panacea.
>> 
>> What is a phase microstepper and/or how does it compare to a DDS?
>> 
>> (Google gets lots of hits, but they all refer to motors.)
> 
> 
> H-maser aging is typically compensated by something like
> spectratime femto-stepper
> http://www.spectratime.com/products/itest/clock-instruments/FemtoStepper/
> microsemi AOG
> http://www.microsemi.com/products/timing-synchronization-systems/time-frequency-references/active-hydrogen-maser/aog-110
> (there are probably others, please post if you know about them!)
> 
> afaik they contain a OCXO/BVA that is steered based on a DMTD measurement
> against the input reference.
> 
> 
> AW
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Re: [time-nuts] NCOCXO anyone?

[Richard (Rick) Karlquist]

On 7/22/2016 2:22 AM, Attila Kinali wrote:

Hoi Rick,

On Thu, 21 Jul 2016 18:47:24 -0700
"Richard (Rick) Karlquist"  wrote:


Also in 1996, phase microsteppers were already legacy
technology and didn't have a good reputation for spectral
purity.  Another non-panacea.


If they are legacy, what is current state of the art?
And is that how your DDS approach came to be?


Attila Kinali




Yes the DDS papers of 1995/1996 were in response to
the limitations of phase microsteppers.  I have been
out of the precision frequency field since 1998,
so I can't speak for the current state of the art.

Rick
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Re: [time-nuts] NCOCXO anyone?

[Attila Kinali]

On Thu, 21 Jul 2016 22:22:14 -0500
David  wrote:

> Increased integration has only helped insofar as you can attempt
> designs which would have been prohibitive before.
> 
> I keep trying to come up with a charge balancing design but what about
> Linear Technology's solution from back in 2001?
> 
> A Standards Lab Grade 20-Bit DAC with 0.1ppm/°C Drift
> http://www.linear.com/docs/4177

You can already get 24bit DAC's off the shelf from TI (DAC1282).
I do not know how stable they are in reality. I looked into high
precision DAC's a year or two ago and figured out that once you
cross the 20bit line, all kind of weird stuff happens that is
hard or almost impossible to compensate for. The trick with using
an ADC (which are available up to 32bit) doesn't really work either,
as offset drifts, thermal voltage etc are hard to impossible to
compensate completely. If you go through the volt-nuts mailinglist,
you'll see how much effort it is to even keep 1ppm (~20bit) stability
of a voltage reference... and then to get that performance out of a DAC.

If anything, I think the better approach is to use high resolution DAC
like the DAC1282 or maybe the DAC1280 with a custom modulator and put
it inside the control loop such that the real measurement happens in
the frequency/time domain. The results from Sherman & Jördens[1]
seems to indicate that sub-100fs stability should be possible, though
there are a couple of open questions there.

Attila Kinali


[1] "Oscillator metrology with software defined radio",
by Jeff Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
(it's available from NIST as well)
-- 
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] NCOCXO anyone?

[Bruce Griffiths]

No, the first one merely uses a pair of cascaded heterodyne PLLs as shown on p3 
of the manual.A diophantine setup may be useful here if one wished to construct 
something similar.

Bruce


  From: Anders Wallin <anders.e.e.wal...@gmail.com>
 To: Discussion of precise time and frequency measurement <time-nuts@febo.com> 
 Sent: Friday, 22 July 2016 7:49 PM
 Subject: Re: [time-nuts] NCOCXO anyone?
   
> rich...@karlquist.com said:
> > Also in 1996, phase microsteppers were already legacy technology and
> didn't
> > have a good reputation for spectral purity.  Another non-panacea.
>
> What is a phase microstepper and/or how does it compare to a DDS?
>
> (Google gets lots of hits, but they all refer to motors.)
>


H-maser aging is typically compensated by something like
spectratime femto-stepper
http://www.spectratime.com/products/itest/clock-instruments/FemtoStepper/
microsemi AOG
http://www.microsemi.com/products/timing-synchronization-systems/time-frequency-references/active-hydrogen-maser/aog-110
(there are probably others, please post if you know about them!)

afaik they contain a OCXO/BVA that is steered based on a DMTD measurement
against the input reference.


AW
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Re: [time-nuts] NCOCXO anyone?

[Anders Wallin]

> rich...@karlquist.com said:
> > Also in 1996, phase microsteppers were already legacy technology and
> didn't
> > have a good reputation for spectral purity.  Another non-panacea.
>
> What is a phase microstepper and/or how does it compare to a DDS?
>
> (Google gets lots of hits, but they all refer to motors.)
>


H-maser aging is typically compensated by something like
spectratime femto-stepper
http://www.spectratime.com/products/itest/clock-instruments/FemtoStepper/
microsemi AOG
http://www.microsemi.com/products/timing-synchronization-systems/time-frequency-references/active-hydrogen-maser/aog-110
(there are probably others, please post if you know about them!)

afaik they contain a OCXO/BVA that is steered based on a DMTD measurement
against the input reference.


AW
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Re: [time-nuts] NCOCXO anyone?

[Hal Murray]

rich...@karlquist.com said:
> Also in 1996, phase microsteppers were already legacy technology and didn't
> have a good reputation for spectral purity.  Another non-panacea. 

What is a phase microstepper and/or how does it compare to a DDS?

(Google gets lots of hits, but they all refer to motors.)


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] NCOCXO anyone?

[David]

On Thu, 21 Jul 2016 18:47:24 -0700, you wrote:

>On 7/21/2016 4:56 PM, Nick Sayer via time-nuts wrote:
>
>> Oh my. That’s a bit more than I was originally considering… What I had in 
>> mind was adding a DAC front end to an OCXO so that you could tune the EFC 
>> with serial commands rather than analog and calling that a product.
>>
>
>20 years ago when HP was working on a so called "smart clock"
>GPS box, they decided to do what you said, use a DAC to
>tune the EFC on the E1938A oscillator.  I
>recommended to them NOT to try to do that, but they
>didn't listen to me.  At that time, it
>was nearly impossible to come up with a DAC, buffer
>amplifier, and voltage reference that didn't degrade
>the stability of the E1938A, which isn't even as stable
>as a 10811.  What you need to ask yourself is:  in
>2016, can I finally get analog components that are
>an order of magnitude or two better than what was
>available in 1996?  I don't know, without researching
>it.  Certainly, we can't depend on Moore's law coming
>to the rescue.  If anything, that works against analog
>IC's by obsoleting older analog processes.
>
>Also in 1996, phase microsteppers were already legacy
>technology and didn't have a good reputation for spectral
>purity.  Another non-panacea.
>
>Rick

Increased integration has only helped insofar as you can attempt
designs which would have been prohibitive before.

I keep trying to come up with a charge balancing design but what about
Linear Technology's solution from back in 2001?

A Standards Lab Grade 20-Bit DAC with 0.1ppm/°C Drift
http://www.linear.com/docs/4177
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Re: [time-nuts] NCOCXO anyone?

[Richard (Rick) Karlquist]

On 7/21/2016 4:56 PM, Nick Sayer via time-nuts wrote:

Oh my. That’s a bit more than I was originally considering… What I had in mind 
was adding a DAC front end to an OCXO so that you could tune the EFC with 
serial commands rather than analog and calling that a product.



20 years ago when HP was working on a so called "smart clock"
GPS box, they decided to do what you said, use a DAC to
tune the EFC on the E1938A oscillator.  I
recommended to them NOT to try to do that, but they
didn't listen to me.  At that time, it
was nearly impossible to come up with a DAC, buffer
amplifier, and voltage reference that didn't degrade
the stability of the E1938A, which isn't even as stable
as a 10811.  What you need to ask yourself is:  in
2016, can I finally get analog components that are
an order of magnitude or two better than what was
available in 1996?  I don't know, without researching
it.  Certainly, we can't depend on Moore's law coming
to the rescue.  If anything, that works against analog
IC's by obsoleting older analog processes.

Also in 1996, phase microsteppers were already legacy
technology and didn't have a good reputation for spectral
purity.  Another non-panacea.

Rick
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Re: [time-nuts] NCOCXO anyone?

[Bob Camp]

Hi

Ideally a phase micro stepper would have an ADEV floor that is lower than 
anything you would run through it. 
That way the ADEV in would be the same as the ADEV out. Since there are things 
out there that are lower
ADEV than an OCXO, that’s not a good thing to put in the middle of the beast. 

Bob


> On Jul 21, 2016, at 7:56 PM, Nick Sayer via time-nuts <time-nuts@febo.com> 
> wrote:
> 
> Oh my. That’s a bit more than I was originally considering… What I had in 
> mind was adding a DAC front end to an OCXO so that you could tune the EFC 
> with serial commands rather than analog and calling that a product.
> 
> A simple version of what you seem to be describing, however, *sounds* to me 
> something like this:
> 
> The microcontroller has the same phase discriminator system the GPSDO has, 
> except that instead of the reference signal coming from a PPS, it comes from 
> an input reference. The microcontroller can get a phase difference reading 
> between the oscillator output and the reference and in software can tune the 
> oscillator DAC output to arrange for a certain rate-of-change, adjustable via 
> serial commands.
> 
> Does that sound about right?
> 
> Perhaps a more traditional PLL approach - using the 4046 PC2 output with an 
> RC and simply allowing the controller to sample that makes some sense 
> (calibrating it may be painful). I’ll have to do some more thinking about it. 
> :)
> 
>> On Jul 21, 2016, at 3:39 PM, Tom Van Baak <t...@leapsecond.com> wrote:
>> 
>> Hi Nick,
>> 
>> There may be several threads in the time-nuts archives related to your 
>> question. The greater concept is a phase microstepper (aka microphase 
>> stepper). Imagine a small board that takes =10 MHz in and puts ~10 MHz out. 
>> Using RS232 (or SPI or I2C) you control the phase, or even the phase over 
>> time, which is to say, the frequency offset. Maybe do it with analog (EFC). 
>> Maybe do it with digital (DDS).
>> 
>> There are highly-prized commercial instruments that do this. But no amateur 
>> has tried yet. You should be the first. If you think about what we do with 
>> steering oscillators -- for GPSDO, or for dual-mixers, or for home time 
>> scales, or even sidereal or mars time -- having a device that cleanly steers 
>> phase and frequency with simple RS232 would be very useful. For example, it 
>> would allow anyone to steer a Rb or Cs standard, even though many of these 
>> lab instruments do not have analog EFC or digital tuning options.
>> 
>> The possibility of this at the amateur level occurred to me when I played 
>> with Bert's 9913:
>> 
>> http://leapsecond.com/pages/ad9913/
>> 
>> Read especially about the "programmable modulus mode" which can be used to 
>> avoid truncation errors and achieve perfect long-term phase; kind of like 
>> the difference between PLL and FLL in a GPSDO's 1PPS.
>> 
>> Look also at how the amazing FE-405 oscillator works:
>> 
>> http://leapsecond.com/pages/fe405/
>> 
>> And the idea of [mis]using a DDS as a high-resolution phase measurement 
>> technique was confirmed with the PicoPak project:
>> 
>> http://www.wriley.com/PicoPak%20App%20Notes%20Links.htm
>> 
>> So, yes, please take the bait and play with all aspects of your NCOCXO idea.
>> 
>> /tvb
>> 
>> - Original Message - 
>> From: "Nick Sayer via time-nuts" <time-nuts@febo.com>
>> To: "Chris Arnold via time-nuts" <time-nuts@febo.com>
>> Sent: Thursday, July 21, 2016 10:05 AM
>> Subject: [time-nuts] NCOCXO anyone?
>> 
>> 
>>> Would anyone see any value in a board that had an OH300 with a serial 
>>> interface for tuning?
>>> 
>>> I had a thought perhaps to make one starting with my GPSDO and just 
>>> ditching the GPS part and possibly adding an RS-232 level converter.  I 
>>> could conceivably bring it all out to a DB9 and emulate an FE-5680 
>>> (obviously it's long term stability would be poorer without some 
>>> discipline) or just make my own protocol up. 
>>> 
>>> Sent from my iPhone
>> 
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Re: [time-nuts] NCOCXO anyone?

[Bob Camp]

Hi


> On Jul 21, 2016, at 7:17 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message <4763643485B04450A76F7C04BA8CFB63@pc52>, "Tom Van Baak" writes:
> 
>> There are highly-prized commercial instruments that do this. But
>> no amateur has tried yet.
> 
> It would be more precise to say that no amateur has been willing to
> talk about their results yet.
> 
> I personally know several have tried and failed at various levels
> of performance.
> 
> My own personal experience, both analog and VHDL, is that there is
> a particularly long and noisy way from theory to practice in this
> space.
> 
> The one thing I have *not* tried, and the only one I think has any
> realistic chances, is to use a DDS chip which has a phase modulation
> register.

If you go the DDS route, it really needs a post filter to make it “fly right”. 
The narrower the
filter, the better it gets. Pretty quickly you are into an ovenized filter.  Is 
that better or worse
than an ovenized phase modulator? Not at all clear.

Bob

> 
> That should get you to a nanosecond without too much trouble.
> 
> -- 
> 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] NCOCXO anyone?

[Nick Sayer via time-nuts]

Oh my. That’s a bit more than I was originally considering… What I had in mind 
was adding a DAC front end to an OCXO so that you could tune the EFC with 
serial commands rather than analog and calling that a product.

A simple version of what you seem to be describing, however, *sounds* to me 
something like this:

The microcontroller has the same phase discriminator system the GPSDO has, 
except that instead of the reference signal coming from a PPS, it comes from an 
input reference. The microcontroller can get a phase difference reading between 
the oscillator output and the reference and in software can tune the oscillator 
DAC output to arrange for a certain rate-of-change, adjustable via serial 
commands.

Does that sound about right?

Perhaps a more traditional PLL approach - using the 4046 PC2 output with an RC 
and simply allowing the controller to sample that makes some sense (calibrating 
it may be painful). I’ll have to do some more thinking about it. :)

> On Jul 21, 2016, at 3:39 PM, Tom Van Baak <t...@leapsecond.com> wrote:
> 
> Hi Nick,
> 
> There may be several threads in the time-nuts archives related to your 
> question. The greater concept is a phase microstepper (aka microphase 
> stepper). Imagine a small board that takes =10 MHz in and puts ~10 MHz out. 
> Using RS232 (or SPI or I2C) you control the phase, or even the phase over 
> time, which is to say, the frequency offset. Maybe do it with analog (EFC). 
> Maybe do it with digital (DDS).
> 
> There are highly-prized commercial instruments that do this. But no amateur 
> has tried yet. You should be the first. If you think about what we do with 
> steering oscillators -- for GPSDO, or for dual-mixers, or for home time 
> scales, or even sidereal or mars time -- having a device that cleanly steers 
> phase and frequency with simple RS232 would be very useful. For example, it 
> would allow anyone to steer a Rb or Cs standard, even though many of these 
> lab instruments do not have analog EFC or digital tuning options.
> 
> The possibility of this at the amateur level occurred to me when I played 
> with Bert's 9913:
> 
> http://leapsecond.com/pages/ad9913/
> 
> Read especially about the "programmable modulus mode" which can be used to 
> avoid truncation errors and achieve perfect long-term phase; kind of like the 
> difference between PLL and FLL in a GPSDO's 1PPS.
> 
> Look also at how the amazing FE-405 oscillator works:
> 
> http://leapsecond.com/pages/fe405/
> 
> And the idea of [mis]using a DDS as a high-resolution phase measurement 
> technique was confirmed with the PicoPak project:
> 
> http://www.wriley.com/PicoPak%20App%20Notes%20Links.htm
> 
> So, yes, please take the bait and play with all aspects of your NCOCXO idea.
> 
> /tvb
> 
> - Original Message - 
> From: "Nick Sayer via time-nuts" <time-nuts@febo.com>
> To: "Chris Arnold via time-nuts" <time-nuts@febo.com>
> Sent: Thursday, July 21, 2016 10:05 AM
> Subject: [time-nuts] NCOCXO anyone?
> 
> 
>> Would anyone see any value in a board that had an OH300 with a serial 
>> interface for tuning?
>> 
>> I had a thought perhaps to make one starting with my GPSDO and just ditching 
>> the GPS part and possibly adding an RS-232 level converter.  I could 
>> conceivably bring it all out to a DB9 and emulate an FE-5680 (obviously it's 
>> long term stability would be poorer without some discipline) or just make my 
>> own protocol up. 
>> 
>> Sent from my iPhone
> 
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Re: [time-nuts] NCOCXO anyone?

[Poul-Henning Kamp]

In message <4763643485B04450A76F7C04BA8CFB63@pc52>, "Tom Van Baak" writes:

>There are highly-prized commercial instruments that do this. But
>no amateur has tried yet.

It would be more precise to say that no amateur has been willing to
talk about their results yet.

I personally know several have tried and failed at various levels
of performance.

My own personal experience, both analog and VHDL, is that there is
a particularly long and noisy way from theory to practice in this
space.

The one thing I have *not* tried, and the only one I think has any
realistic chances, is to use a DDS chip which has a phase modulation
register.

That should get you to a nanosecond without too much trouble.

-- 
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] NCOCXO anyone?

[Tom Van Baak]

Hi Nick,

There may be several threads in the time-nuts archives related to your 
question. The greater concept is a phase microstepper (aka microphase stepper). 
Imagine a small board that takes =10 MHz in and puts ~10 MHz out. Using RS232 
(or SPI or I2C) you control the phase, or even the phase over time, which is to 
say, the frequency offset. Maybe do it with analog (EFC). Maybe do it with 
digital (DDS).

There are highly-prized commercial instruments that do this. But no amateur has 
tried yet. You should be the first. If you think about what we do with steering 
oscillators -- for GPSDO, or for dual-mixers, or for home time scales, or even 
sidereal or mars time -- having a device that cleanly steers phase and 
frequency with simple RS232 would be very useful. For example, it would allow 
anyone to steer a Rb or Cs standard, even though many of these lab instruments 
do not have analog EFC or digital tuning options.

The possibility of this at the amateur level occurred to me when I played with 
Bert's 9913:

http://leapsecond.com/pages/ad9913/

Read especially about the "programmable modulus mode" which can be used to 
avoid truncation errors and achieve perfect long-term phase; kind of like the 
difference between PLL and FLL in a GPSDO's 1PPS.

Look also at how the amazing FE-405 oscillator works:

http://leapsecond.com/pages/fe405/

And the idea of [mis]using a DDS as a high-resolution phase measurement 
technique was confirmed with the PicoPak project:

http://www.wriley.com/PicoPak%20App%20Notes%20Links.htm

So, yes, please take the bait and play with all aspects of your NCOCXO idea.

/tvb

- Original Message - 
From: "Nick Sayer via time-nuts" <time-nuts@febo.com>
To: "Chris Arnold via time-nuts" <time-nuts@febo.com>
Sent: Thursday, July 21, 2016 10:05 AM
Subject: [time-nuts] NCOCXO anyone?


> Would anyone see any value in a board that had an OH300 with a serial 
> interface for tuning?
> 
> I had a thought perhaps to make one starting with my GPSDO and just ditching 
> the GPS part and possibly adding an RS-232 level converter.  I could 
> conceivably bring it all out to a DB9 and emulate an FE-5680 (obviously it's 
> long term stability would be poorer without some discipline) or just make my 
> own protocol up. 
> 
> Sent from my iPhone

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[time-nuts] NCOCXO anyone?

[Nick Sayer via time-nuts]

Would anyone see any value in a board that had an OH300 with a serial interface 
for tuning?

I had a thought perhaps to make one starting with my GPSDO and just ditching 
the GPS part and possibly adding an RS-232 level converter.  I could 
conceivably bring it all out to a DB9 and emulate an FE-5680 (obviously it's 
long term stability would be poorer without some discipline) or just make my 
own protocol up. 

Sent from my iPhone
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