Re: [time-nuts] TDC-GPX2 TDC chip

[Bruce Griffiths]

The apparent drift will be determined largely by that of the reference 
oscillator due to the embedded continuous interpolator calibration. Placing it 
in an oven will probably degrade the resolution due to the bin size tempco.

All time interval instruments have an offset between channels, This is easily 
measured and corrected for. 

The performance as stated in the datasheet appears comparable if not better 
than a typical 5370A/B when one takes the various sources of nonlinearity and 
crosstalk in a 5370A/B into account. It certainly consumes less power even 
after the power consumption of a good ocxo is added.  Its also somewhat cheaper.

However a comprehensive evaluation of its performance beyond that given in the 
datasheet is required.

A comprehensive test of the performance of a n actual 5370A/B would also be 
useful.

Bruce

> 
> On 16 March 2017 at 15:54 Bill Byrom  wrote:
> 
> "the large print giveth and the small print taketh away"
> 
> (Quoted from this great description of modern life:
> 
> http://www.tomwaits.com/songs/song/322/Step_Right_Up/ )
> 
> I'm not trying to be too critical, but look carefully at the datasheet
> for that part:
> http://ams.com/eng/content/download/951531/2270299/381482
> 
> The "accuracy" can in no way be described as 10 ps. In high
> resolution mode:
> 
> * Single shot RMS time resolution: 10 ps typical, 15 ps maximum
> 
> * Integral non-linearity: 20 ps max
> 
> * Differential non-linearity: 5 ps typ
> 
> * Channel to channel isolation: 20 ps typ, 100 ps max
> 
> * Offset error: 200 ps typ
> 
> * Offset error drift vs temperature: 1.5 ps typ, 3 ps max / K
> 
> * FWHM (full width half maximum) histogram: 20-25 ps
> 
> So if the temperature changes 6 F (3.3 C), the measurement may drift by
> 10 ps. The single shot absolute uncertainty due to jitter (see the
> histogram) could easily be +/- 25 ps. There is no mention of long-term
> drift, since that isn't a typical use of this part. It would be
> interesting to put one in a simple oven and see how it drifts over a
> 
> few months.
> --
> 
> Bill Byrom N5BB
> 
> - Original message -
> 
> From: Christopher Hoover 
> 
> To: Discussion of precise time and frequency measurement 
> 
> Subject: [time-nuts] TDC-GPX2 TDC chip
> 
> Date: Wed, 15 Mar 2017 15:28:20 -0700
> 
> 
> http://ams.com/eng/Products/Precision-Time-Measurement/Time-to-Digital-Converters/TDC-GPX2
> 
> Claims to have single-shot accuracy of 10 ps.
> 
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Re: [time-nuts] TDC-GPX2 TDC chip

[Bill Byrom]

"the large print giveth and the small print taketh away"

(Quoted from this great description of modern life:

http://www.tomwaits.com/songs/song/322/Step_Right_Up/ )



I'm not trying to be too critical, but look carefully at the datasheet
for that part:
http://ams.com/eng/content/download/951531/2270299/381482 



The "accuracy" can in no way be described as 10 ps. In high
resolution mode:
* Single shot RMS time resolution: 10 ps typical, 15 ps maximum

* Integral non-linearity: 20 ps max

* Differential non-linearity: 5 ps typ

* Channel to channel isolation: 20 ps typ, 100 ps max

* Offset error: 200 ps typ

* Offset error drift vs temperature: 1.5 ps typ, 3 ps max / K

* FWHM (full width half maximum) histogram: 20-25 ps



So if the temperature changes 6 F (3.3 C), the measurement may drift by
10 ps. The single shot absolute uncertainty due to jitter (see the
histogram) could easily be +/- 25 ps. There is no mention of long-term
drift, since that isn't a typical use of this part. It would be
interesting to put one in a simple oven and see how it drifts over a
few months.
--

Bill Byrom N5BB







- Original message -

From: Christopher Hoover 

To: Discussion of precise time and frequency measurement 
Subject: [time-nuts] TDC-GPX2 TDC chip

Date: Wed, 15 Mar 2017 15:28:20 -0700



http://ams.com/eng/Products/Precision-Time-Measurement/Time-to-Digital-Converters/TDC-GPX2


Claims to have single-shot accuracy of 10 ps.

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Re: [time-nuts] TDC-GPX2 TDC chip

[Bruce Griffiths]

The datasheet is less than convincing.
The change in resolution/noise with time delay isnt well documented.
Performance may differ when a 1MHz reference clock is used as opposed to the 
10MHz clock they appear to have used for some of the plots on the datasheet.
The customer support person appears to know little useful about tdcs.
Have been debating how to establish the actual performance.

A) use random source(s) to produce data for the fill the buckets histogram test.
For statistically useful results an extremely large number of random events is 
required.
e.g. for a 10MHz reference clock and 10ps bits need around 10,000 hits per bin 
for 1% rms
statistical variation in bin event totals. i.e. about 1E8 total events.
With a 1MHz reference clock need at least 1E9 events.

B) Use a pair of 10MHz oscillators with a small frequency offset between them 
one of which is used as the reference clock whilst the other is divided down to 
produce a suitable event rate. The leading edge of each successive event is 
swept slowly at a uniform rate across the reference clock cycle in steps of say 
10fs or so per event. This requires that the sources have very low spur levels 
at least 120dB below the carrier and preferably more.
The reference 10MHz can be divided down to 5MHz, 2MHz or 1MHZ for testing with 
lower reference clock frequencies.

c) As above but use a single 10MHz source that acts both as reference clock for 
the TDC and as the input source for an extremely low spur offset generator, the 
output of which is divided down to create a suitable event rate.

D) Compare the TDC measurements with those obtained with a significantly lower 
noise TDC.
Still (a few of us at least) working on this. Initial crude and somewhat noisy 
setup suggested better than 10ps rms (limited somewhat by jitter of divider 
chain used to produce trigger signal). A later version achieved around 3ps rms. 
However comprehensive testing is still to be done.

Bruce

> 
> On 16 March 2017 at 11:28 Christopher Hoover  wrote:
> 
> 
> http://ams.com/eng/Products/Precision-Time-Measurement/Time-to-Digital-Converters/TDC-GPX2
> 
> Claims to have single-shot accuracy of 10 ps.
> 
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Re: [time-nuts] Bye-Bye Crystals

[Scott Stobbe]

I would be careful to get an all analog tcxo. The digi-trim ones while may
have a decent total error band over temperature  can hop up and down in 100
ppb steps when the temperature straddles two points on its temp comp table.

On Wed, Mar 15, 2017 at 7:06 PM Bob Camp  wrote:

> Hi
>
> > On Mar 15, 2017, at 3:55 PM, Dan Kemppainen 
> wrote:
> >
> > Hi Bob,
> >
> > If one prototypes any crystal oscillator, and runs it on a bench. Then
> builds an 'oven' of sorts and runs it on the same bench. Would you expect
> to see any improvement?
>
> Sure, the XO likely moves 50 to 100 ppm over -30 to +70. You will cut that
> down to a couple of ppm. It’s much easier these
> days to just buy (or salvage) a cheap TCXO to get the same level of
> stability.
>
> One very basic issue: If I just grab a random crystal, it likely is a cut
> that does *not* have a useful turn temperature at all. For
> a proper OCXO you need a crystal with a turn temperature in the practical
> range for your oven. There are many other
> issues.
>
> The key point (just as in the previous message) is that you must have good
> frequency vs temperature data to know if
> you are improving things or not. That involves having a real temperature
> test chamber than can be slewed in a controlled
> fashion and repeatably set to a sequence of temperatures. A typical run
> starts at room, steps down to cold (or up to hot).
> It then steps to the other end and finally steps back to room. Data is
> taken every 10C or so and analyzed to be sure that
> things are not all messed up. One obvious problem / issue would be drift
> during the run. A typical run takes several hours to
> most of a day.
>
> Bob
>
> >
> > In other words for a given oscillator (crystal and electronics, etc),
> will there be any improvements in an oven compared to not in an oven? Or,
> are there other things that outweigh the gains by temp controlling the
> whole thing.
> >
> > Yeah, this is a pretty open question, but I don't really have a feel for
> how good an oscillator needs to be before an oven starts to improve
> things...
> >
> > Dan
> >
> >
> >
> >
> > On 3/15/2017 12:00 PM, time-nuts-requ...@febo.com wrote:
> >> Hi
> >>
> >> Where do you plan on getting an OCXO grade crystal at an odd frequency
> like
> >> that? Much of the performance of a good OCXO is in the crystal. Doing a
> proper
> >> design on one is a lot of work. You *might* think that having a design
> for 5.00
> >> MHz would give you a good design for 5.50 MHz. I have empirical
> evidence that
> >> this isn’t the case. Many years later, I’m still utterly amazed that
> this is the way things
> >> work in the crystal business ….( = it’s not just a design issue, it’s
> also a business decision)
> >>
> >> More or less the crystal needs to be:
> >>
> >> 1) Cut specifically to have a turn at a temperature that makes sense
> for your application.
> >> 2) A “large blank” design (for it’s frequency)
> >> 3) In a cold weld package (most of the normal crystals are resistance
> weld)
> >> 4) Run through a high vacuum / high temperature process
> >> 5) Be plated with gold rather than something like silver or aluminum
> (unless it’s at VHF).
> >> 6) Have a motional capacitance that makes sense for your EFC range (
> normally = minimize)
> >> 7) Preferably be an SC or modified SC cut.
> >>
> >> This is for a high stability part. The list does keep going on for a
> while, but that should
> >> give you a pretty good idea.
> >>
> >> Bob
> > ___
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[time-nuts] TDC-GPX2 TDC chip

[Christopher Hoover]

http://ams.com/eng/Products/Precision-Time-Measurement/Time-to-Digital-Converters/TDC-GPX2

Claims to have single-shot accuracy of 10 ps.
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Re: [time-nuts] Bye-Bye Crystals

[Bob Camp]

Hi

Ok, I missed that. 

Unless there is also a trimmer cap, the EFC will be >> 0.01Hz if it needs to be 
on frequency for any rational amount of time. If the crystals are the typical 
old fundamentals, 
they may age 5 to 10 ppm / year when heated to OCXO temperatures. That’s +/- 25 
to +/-
50 Hz just for the first year. 

Bob

> On Mar 15, 2017, at 6:11 PM, Bruce Griffiths  
> wrote:
> 
> Bob
> 
> He stated 0.01Hz EFC tuning range was adequate.
> Gave no spec as to how close to nominal frequency is required though.
> 
> Bruce
>> On 16 March 2017 at 10:53 Bob Camp  wrote:
>> 
>> 
>> Hi
>> 
>> By most modern definitions, “high stability” starts around 1x10^-12 (1 ppt)  
>> at a tau of 1 second to 
>> 10 seconds. There are $20 eBay OCXO’s that run at that level.  With a 
>> fundamental crystal you 
>> aren’t going to get to that point. 
>> 
>> How much EFC range are you after? 
>> 
>> How good a CNC setup do you have?
>> 
>> What kind of temperature test setup do you have? 
>> 
>> Simply put, the design approach is a “test over temperature / collect data 
>> -> optimize” loop. 
>> Without good frequency vs temperature data, you are flying totally blind. 
>> Even on a production
>> design, this is how it’s done. The parts you fiddle are likely to be odd 
>> shaped chunks of metal 
>> that fit here or there. 
>> 
>> Bob
>> 
>>> On Mar 15, 2017, at 3:36 PM, Gilles Clement  
>>> wrote:
>>> 
>>> Hi, 
>>> I have a bunch of 5.184Mhz crystals. Large metallic tanks: HC33U case
>>> Maybe not OCXO grade, but I build a simple oscillator with a 4060 chip
>>> placed in a double oven, and reached 10E-9 short term stability up to 10sec 
>>> tau.
>>> Not bad, so wondering if I can get better with a more advanced design. 
>>> Gilles. 
>>> 
>>> 
 Le 15 mars 2017 à 12:45, Bob Camp  a écrit :
 
 Hi
 
 Where do you plan on getting an OCXO grade crystal at an odd frequency 
 like 
 that? Much of the performance of a good OCXO is in the crystal. Doing a 
 proper 
 design on one is a lot of work. You *might* think that having a design for 
 5.00
 MHz would give you a good design for 5.50 MHz. I have empirical 
 evidence that
 this isn’t the case. Many years later, I’m still utterly amazed that this 
 is the way things
 work in the crystal business ….( = it’s not just a design issue, it’s also 
 a business decision) 
 
 More or less the crystal needs to be:
 
 1) Cut specifically to have a turn at a temperature that makes sense for 
 your application.
 2) A “large blank” design (for it’s frequency)
 3) In a cold weld package (most of the normal crystals are resistance weld)
 4) Run through a high vacuum / high temperature process
 5) Be plated with gold rather than something like silver or aluminum 
 (unless it’s at VHF).
 6) Have a motional capacitance that makes sense for your EFC range ( 
 normally = minimize)
 7) Preferably be an SC or modified SC cut. 
 
 This is for a high stability part. The list does keep going on for a 
 while, but that should 
 give you a pretty good idea. 
 
 Bob
 
> On Mar 15, 2017, at 3:11 AM, Gilles Clement  
> wrote:
> 
> Hi, 
> So what is the « best » design for DIY a high stability OCVXO ? 
> I am looking after one, needed for an exotic frequency : 5184kHZ 
> Thx, 
> Gilles. 
> 
> 
>> Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist 
>>  a écrit :
>> 
>> 
>> 
>> On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
>> 
>>> 
>>> Looking at oscillator circuits like the HP10811A will give some idea of 
>>> some of the additional complexity required for a overtone operation. 
>>> Dissecting a few ocxos may also be helpful. Some start with a 10MHz 
>>> crystal and a Colpitts sustaining stage and use a 74HC74 or similar to  
>>> divide the 10Mhz by 2 and drive the output pin. Even when a sinewave 
>>> output is required often a CMOS inverter drives the output pin via an 
>>> LC filter.
>>> 
>>> Bruce
>>> 
>> 
>> I don't agree here.  The 10811 is not a good tutorial for general 
>> oscillator design.  Because it is SC cut, it has a complicated
>> mode suppression network across the base emitter junction to
>> suppress mode B as well as the fundamental.
>> 
>> The E1983A oscillator uses the same crystal (in a low profile
>> package).  You can read my paper about it and see that I
>> used a very simple bridged tee oscillator circuit.  That is
>> all you need to select the right overtone and mode.
>> 
>> This is the same circuit that I used at Zeta Labs 40 years
>> ago to design hundreds of custom VCXO's, up to the 9th
>> overtone.  It simply worked every time, unlike 

Re: [time-nuts] Bye-Bye Crystals

[Bruce Griffiths]

Bob

He stated 0.01Hz EFC tuning range was adequate.
Gave no spec as to how close to nominal frequency is required though.

Bruce
> On 16 March 2017 at 10:53 Bob Camp  wrote:
> 
> 
> Hi
> 
> By most modern definitions, “high stability” starts around 1x10^-12 (1 ppt)  
> at a tau of 1 second to 
> 10 seconds. There are $20 eBay OCXO’s that run at that level.  With a 
> fundamental crystal you 
> aren’t going to get to that point. 
> 
> How much EFC range are you after? 
> 
> How good a CNC setup do you have?
> 
> What kind of temperature test setup do you have? 
> 
> Simply put, the design approach is a “test over temperature / collect data -> 
> optimize” loop. 
> Without good frequency vs temperature data, you are flying totally blind. 
> Even on a production
> design, this is how it’s done. The parts you fiddle are likely to be odd 
> shaped chunks of metal 
> that fit here or there. 
> 
> Bob
> 
> > On Mar 15, 2017, at 3:36 PM, Gilles Clement  
> > wrote:
> > 
> > Hi, 
> > I have a bunch of 5.184Mhz crystals. Large metallic tanks: HC33U case
> > Maybe not OCXO grade, but I build a simple oscillator with a 4060 chip
> > placed in a double oven, and reached 10E-9 short term stability up to 10sec 
> > tau.
> > Not bad, so wondering if I can get better with a more advanced design. 
> > Gilles. 
> > 
> > 
> >> Le 15 mars 2017 à 12:45, Bob Camp  a écrit :
> >> 
> >> Hi
> >> 
> >> Where do you plan on getting an OCXO grade crystal at an odd frequency 
> >> like 
> >> that? Much of the performance of a good OCXO is in the crystal. Doing a 
> >> proper 
> >> design on one is a lot of work. You *might* think that having a design for 
> >> 5.00
> >> MHz would give you a good design for 5.50 MHz. I have empirical 
> >> evidence that
> >> this isn’t the case. Many years later, I’m still utterly amazed that this 
> >> is the way things
> >> work in the crystal business ….( = it’s not just a design issue, it’s also 
> >> a business decision) 
> >> 
> >> More or less the crystal needs to be:
> >> 
> >> 1) Cut specifically to have a turn at a temperature that makes sense for 
> >> your application.
> >> 2) A “large blank” design (for it’s frequency)
> >> 3) In a cold weld package (most of the normal crystals are resistance weld)
> >> 4) Run through a high vacuum / high temperature process
> >> 5) Be plated with gold rather than something like silver or aluminum 
> >> (unless it’s at VHF).
> >> 6) Have a motional capacitance that makes sense for your EFC range ( 
> >> normally = minimize)
> >> 7) Preferably be an SC or modified SC cut. 
> >> 
> >> This is for a high stability part. The list does keep going on for a 
> >> while, but that should 
> >> give you a pretty good idea. 
> >> 
> >> Bob
> >> 
> >>> On Mar 15, 2017, at 3:11 AM, Gilles Clement  
> >>> wrote:
> >>> 
> >>> Hi, 
> >>> So what is the « best » design for DIY a high stability OCVXO ? 
> >>> I am looking after one, needed for an exotic frequency : 5184kHZ 
> >>> Thx, 
> >>> Gilles. 
> >>> 
> >>> 
>  Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist 
>   a écrit :
>  
>  
>  
>  On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
>  
> > 
> > Looking at oscillator circuits like the HP10811A will give some idea of 
> > some of the additional complexity required for a overtone operation. 
> > Dissecting a few ocxos may also be helpful. Some start with a 10MHz 
> > crystal and a Colpitts sustaining stage and use a 74HC74 or similar to  
> > divide the 10Mhz by 2 and drive the output pin. Even when a sinewave 
> > output is required often a CMOS inverter drives the output pin via an 
> > LC filter.
> > 
> > Bruce
> > 
>  
>  I don't agree here.  The 10811 is not a good tutorial for general 
>  oscillator design.  Because it is SC cut, it has a complicated
>  mode suppression network across the base emitter junction to
>  suppress mode B as well as the fundamental.
>  
>  The E1983A oscillator uses the same crystal (in a low profile
>  package).  You can read my paper about it and see that I
>  used a very simple bridged tee oscillator circuit.  That is
>  all you need to select the right overtone and mode.
>  
>  This is the same circuit that I used at Zeta Labs 40 years
>  ago to design hundreds of custom VCXO's, up to the 9th
>  overtone.  It simply worked every time, unlike various other
>  designs that were in use at Zeta.
>  
>  Around 1985, I got a consulting gig at Equatorial Communications
>  to redesign their 5th overtone VCXO.  Only about half of the
>  crystals would work in their circuit.  They had thousands
>  of "reject" crystals.  I just used my old Zeta circuit and
>  all the crystals started working again.
>  
>  Equatorial owned the 10 meter dish that you used to see on
> 

Re: [time-nuts] Bye-Bye Crystals

[Bob Camp]

Hi

> On Mar 15, 2017, at 3:55 PM, Dan Kemppainen  wrote:
> 
> Hi Bob,
> 
> If one prototypes any crystal oscillator, and runs it on a bench. Then builds 
> an 'oven' of sorts and runs it on the same bench. Would you expect to see any 
> improvement?

Sure, the XO likely moves 50 to 100 ppm over -30 to +70. You will cut that down 
to a couple of ppm. It’s much easier these 
days to just buy (or salvage) a cheap TCXO to get the same level of stability. 

One very basic issue: If I just grab a random crystal, it likely is a cut that 
does *not* have a useful turn temperature at all. For
a proper OCXO you need a crystal with a turn temperature in the practical range 
for your oven. There are many other 
issues. 

The key point (just as in the previous message) is that you must have good 
frequency vs temperature data to know if 
you are improving things or not. That involves having a real temperature test 
chamber than can be slewed in a controlled 
fashion and repeatably set to a sequence of temperatures. A typical run starts 
at room, steps down to cold (or up to hot). 
It then steps to the other end and finally steps back to room. Data is taken 
every 10C or so and analyzed to be sure that 
things are not all messed up. One obvious problem / issue would be drift during 
the run. A typical run takes several hours to
most of a day. 

Bob

> 
> In other words for a given oscillator (crystal and electronics, etc), will 
> there be any improvements in an oven compared to not in an oven? Or, are 
> there other things that outweigh the gains by temp controlling the whole 
> thing.
> 
> Yeah, this is a pretty open question, but I don't really have a feel for how 
> good an oscillator needs to be before an oven starts to improve things...
> 
> Dan
> 
> 
> 
> 
> On 3/15/2017 12:00 PM, time-nuts-requ...@febo.com wrote:
>> Hi
>> 
>> Where do you plan on getting an OCXO grade crystal at an odd frequency like
>> that? Much of the performance of a good OCXO is in the crystal. Doing a 
>> proper
>> design on one is a lot of work. You *might* think that having a design for 
>> 5.00
>> MHz would give you a good design for 5.50 MHz. I have empirical evidence 
>> that
>> this isn’t the case. Many years later, I’m still utterly amazed that this is 
>> the way things
>> work in the crystal business ….( = it’s not just a design issue, it’s also a 
>> business decision)
>> 
>> More or less the crystal needs to be:
>> 
>> 1) Cut specifically to have a turn at a temperature that makes sense for 
>> your application.
>> 2) A “large blank” design (for it’s frequency)
>> 3) In a cold weld package (most of the normal crystals are resistance weld)
>> 4) Run through a high vacuum / high temperature process
>> 5) Be plated with gold rather than something like silver or aluminum (unless 
>> it’s at VHF).
>> 6) Have a motional capacitance that makes sense for your EFC range ( 
>> normally = minimize)
>> 7) Preferably be an SC or modified SC cut.
>> 
>> This is for a high stability part. The list does keep going on for a while, 
>> but that should
>> give you a pretty good idea.
>> 
>> Bob
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Re: [time-nuts] Bye-Bye Crystals

[Bob Camp]

Hi

By most modern definitions, “high stability” starts around 1x10^-12 (1 ppt)  at 
a tau of 1 second to 
10 seconds. There are $20 eBay OCXO’s that run at that level.  With a 
fundamental crystal you 
aren’t going to get to that point. 

How much EFC range are you after? 

How good a CNC setup do you have?

What kind of temperature test setup do you have? 

Simply put, the design approach is a “test over temperature / collect data -> 
optimize” loop. 
Without good frequency vs temperature data, you are flying totally blind. Even 
on a production
design, this is how it’s done. The parts you fiddle are likely to be odd shaped 
chunks of metal 
that fit here or there. 

Bob

> On Mar 15, 2017, at 3:36 PM, Gilles Clement  wrote:
> 
> Hi, 
> I have a bunch of 5.184Mhz crystals. Large metallic tanks: HC33U case
> Maybe not OCXO grade, but I build a simple oscillator with a 4060 chip
> placed in a double oven, and reached 10E-9 short term stability up to 10sec 
> tau.
> Not bad, so wondering if I can get better with a more advanced design. 
> Gilles. 
> 
> 
>> Le 15 mars 2017 à 12:45, Bob Camp  a écrit :
>> 
>> Hi
>> 
>> Where do you plan on getting an OCXO grade crystal at an odd frequency like 
>> that? Much of the performance of a good OCXO is in the crystal. Doing a 
>> proper 
>> design on one is a lot of work. You *might* think that having a design for 
>> 5.00
>> MHz would give you a good design for 5.50 MHz. I have empirical evidence 
>> that
>> this isn’t the case. Many years later, I’m still utterly amazed that this is 
>> the way things
>> work in the crystal business ….( = it’s not just a design issue, it’s also a 
>> business decision) 
>> 
>> More or less the crystal needs to be:
>> 
>> 1) Cut specifically to have a turn at a temperature that makes sense for 
>> your application.
>> 2) A “large blank” design (for it’s frequency)
>> 3) In a cold weld package (most of the normal crystals are resistance weld)
>> 4) Run through a high vacuum / high temperature process
>> 5) Be plated with gold rather than something like silver or aluminum (unless 
>> it’s at VHF).
>> 6) Have a motional capacitance that makes sense for your EFC range ( 
>> normally = minimize)
>> 7) Preferably be an SC or modified SC cut. 
>> 
>> This is for a high stability part. The list does keep going on for a while, 
>> but that should 
>> give you a pretty good idea. 
>> 
>> Bob
>> 
>>> On Mar 15, 2017, at 3:11 AM, Gilles Clement  
>>> wrote:
>>> 
>>> Hi, 
>>> So what is the « best » design for DIY a high stability OCVXO ? 
>>> I am looking after one, needed for an exotic frequency : 5184kHZ 
>>> Thx, 
>>> Gilles. 
>>> 
>>> 
 Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist  
 a écrit :
 
 
 
 On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
 
> 
> Looking at oscillator circuits like the HP10811A will give some idea of 
> some of the additional complexity required for a overtone operation. 
> Dissecting a few ocxos may also be helpful. Some start with a 10MHz 
> crystal and a Colpitts sustaining stage and use a 74HC74 or similar to  
> divide the 10Mhz by 2 and drive the output pin. Even when a sinewave 
> output is required often a CMOS inverter drives the output pin via an LC 
> filter.
> 
> Bruce
> 
 
 I don't agree here.  The 10811 is not a good tutorial for general 
 oscillator design.  Because it is SC cut, it has a complicated
 mode suppression network across the base emitter junction to
 suppress mode B as well as the fundamental.
 
 The E1983A oscillator uses the same crystal (in a low profile
 package).  You can read my paper about it and see that I
 used a very simple bridged tee oscillator circuit.  That is
 all you need to select the right overtone and mode.
 
 This is the same circuit that I used at Zeta Labs 40 years
 ago to design hundreds of custom VCXO's, up to the 9th
 overtone.  It simply worked every time, unlike various other
 designs that were in use at Zeta.
 
 Around 1985, I got a consulting gig at Equatorial Communications
 to redesign their 5th overtone VCXO.  Only about half of the
 crystals would work in their circuit.  They had thousands
 of "reject" crystals.  I just used my old Zeta circuit and
 all the crystals started working again.
 
 Equatorial owned the 10 meter dish that you used to see on
 your right going south on 237 just before passing over
 Central Expressway in Mountain View.
 
 Rick N6RK
 
 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to 
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Bye-Bye Crystals

[Bruce Griffiths]

Most likely AT cut fundamental (although there are other possibilities.) 
designed for operation around room temperature.

Do you have the manufacturer's specs for these?

What is the change in frequency between room temperature and oven temperature?

What is the operating temperature of the inner oven?

Bruce

> 
> On 16 March 2017 at 08:36 Gilles Clement  
> wrote:
> 
> Hi,
> I have a bunch of 5.184Mhz crystals. Large metallic tanks: HC33U case
> Maybe not OCXO grade, but I build a simple oscillator with a 4060 chip
> placed in a double oven, and reached 10E-9 short term stability up to 
> 10sec tau.
> Not bad, so wondering if I can get better with a more advanced design.
> Gilles.
> 
> > > 
> > Le 15 mars 2017 à 12:45, Bob Camp  a écrit :
> > 
> > Hi
> > 
> > Where do you plan on getting an OCXO grade crystal at an odd 
> > frequency like
> > that? Much of the performance of a good OCXO is in the crystal. 
> > Doing a proper
> > design on one is a lot of work. You *might* think that having a 
> > design for 5.00
> > MHz would give you a good design for 5.50 MHz. I have empirical 
> > evidence that
> > this isn’t the case. Many years later, I’m still utterly amazed 
> > that this is the way things
> > work in the crystal business ….( = it’s not just a design issue, 
> > it’s also a business decision)
> > 
> > More or less the crystal needs to be:
> > 
> > 1) Cut specifically to have a turn at a temperature that makes 
> > sense for your application.
> > 2) A “large blank” design (for it’s frequency)
> > 3) In a cold weld package (most of the normal crystals are 
> > resistance weld)
> > 4) Run through a high vacuum / high temperature process
> > 5) Be plated with gold rather than something like silver or 
> > aluminum (unless it’s at VHF).
> > 6) Have a motional capacitance that makes sense for your EFC range 
> > ( normally = minimize)
> > 7) Preferably be an SC or modified SC cut.
> > 
> > This is for a high stability part. The list does keep going on for 
> > a while, but that should
> > give you a pretty good idea.
> > 
> > Bob
> > 
> > > > > 
> > > On Mar 15, 2017, at 3:11 AM, Gilles Clement 
> > >  wrote:
> > > 
> > > Hi,
> > > So what is the « best » design for DIY a high stability OCVXO 
> > > ?
> > > I am looking after one, needed for an exotic frequency : 
> > > 5184kHZ
> > > Thx,
> > > Gilles.
> > > 
> > > > > > > 
> > > > Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist 
> > > >  a écrit :
> > > > 
> > > > On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
> > > > 
> > > > > > > > > 
> > > > > Looking at oscillator circuits like the HP10811A 
> > > > > will give some idea of some of the additional complexity required for 
> > > > > a overtone operation. Dissecting a few ocxos may also be helpful. 
> > > > > Some start with a 10MHz crystal and a Colpitts sustaining stage and 
> > > > > use a 74HC74 or similar to divide the 10Mhz by 2 and drive the output 
> > > > > pin. Even when a sinewave output is required often a CMOS inverter 
> > > > > drives the output pin via an LC filter.
> > > > > 
> > > > > Bruce
> > > > > 
> > > > > > > > > 
> > > > I don't agree here. The 10811 is not a good tutorial 
> > > > for general oscillator design. Because it is SC cut, it has a 
> > > > complicated
> > > > mode suppression network across the base emitter 
> > > > junction to
> > > > suppress mode B as well as the fundamental.
> > > > 
> > > > The E1983A oscillator uses the same crystal (in a low 
> > > > profile
> > > > package). You can read my paper about it and see that I
> > > > used a very simple bridged tee oscillator circuit. That 
> > > > is
> > > > all you need to select the right overtone and mode.
> > > > 
> > > > This is the same circuit that I used at Zeta Labs 40 
> > > > years
> > > > ago to design hundreds of custom VCXO's, up to the 9th
> > > > overtone. It simply worked every time, unlike various 
> > > > other
> > > > designs that were in use at Zeta.
> > > > 
> > > > Around 1985, I got a consulting gig at Equatorial 
> > > > Communications
> > > > to redesign their 5th overtone VCXO. Only about half of 
> > > > the
> > > > crystals would work in their circuit. They had thousands
> > > > of "reject" crystals. I just used my old Zeta circuit 
> > > > and
> > > > 

Re: [time-nuts] Bye-Bye Crystals

[Dan Kemppainen]

Hi Bob,

If one prototypes any crystal oscillator, and runs it on a bench. Then 
builds an 'oven' of sorts and runs it on the same bench. Would you 
expect to see any improvement?


In other words for a given oscillator (crystal and electronics, etc), 
will there be any improvements in an oven compared to not in an oven? 
Or, are there other things that outweigh the gains by temp controlling 
the whole thing.


Yeah, this is a pretty open question, but I don't really have a feel for 
how good an oscillator needs to be before an oven starts to improve 
things...


Dan




On 3/15/2017 12:00 PM, time-nuts-requ...@febo.com wrote:

Hi

Where do you plan on getting an OCXO grade crystal at an odd frequency like
that? Much of the performance of a good OCXO is in the crystal. Doing a proper
design on one is a lot of work. You *might* think that having a design for 
5.00
MHz would give you a good design for 5.50 MHz. I have empirical evidence 
that
this isn’t the case. Many years later, I’m still utterly amazed that this is 
the way things
work in the crystal business ….( = it’s not just a design issue, it’s also a 
business decision)

More or less the crystal needs to be:

1) Cut specifically to have a turn at a temperature that makes sense for your 
application.
2) A “large blank” design (for it’s frequency)
3) In a cold weld package (most of the normal crystals are resistance weld)
4) Run through a high vacuum / high temperature process
5) Be plated with gold rather than something like silver or aluminum (unless 
it’s at VHF).
6) Have a motional capacitance that makes sense for your EFC range ( normally = 
minimize)
7) Preferably be an SC or modified SC cut.

This is for a high stability part. The list does keep going on for a while, but 
that should
give you a pretty good idea.

Bob

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Re: [time-nuts] Bye-Bye Crystals

[Gilles Clement]

Hi, 
I have a bunch of 5.184Mhz crystals. Large metallic tanks: HC33U case
Maybe not OCXO grade, but I build a simple oscillator with a 4060 chip
placed in a double oven, and reached 10E-9 short term stability up to 10sec tau.
Not bad, so wondering if I can get better with a more advanced design. 
Gilles. 
 

> Le 15 mars 2017 à 12:45, Bob Camp  a écrit :
> 
> Hi
> 
> Where do you plan on getting an OCXO grade crystal at an odd frequency like 
> that? Much of the performance of a good OCXO is in the crystal. Doing a 
> proper 
> design on one is a lot of work. You *might* think that having a design for 
> 5.00
> MHz would give you a good design for 5.50 MHz. I have empirical evidence 
> that
> this isn’t the case. Many years later, I’m still utterly amazed that this is 
> the way things
> work in the crystal business ….( = it’s not just a design issue, it’s also a 
> business decision) 
> 
> More or less the crystal needs to be:
> 
> 1) Cut specifically to have a turn at a temperature that makes sense for your 
> application.
> 2) A “large blank” design (for it’s frequency)
> 3) In a cold weld package (most of the normal crystals are resistance weld)
> 4) Run through a high vacuum / high temperature process
> 5) Be plated with gold rather than something like silver or aluminum (unless 
> it’s at VHF).
> 6) Have a motional capacitance that makes sense for your EFC range ( normally 
> = minimize)
> 7) Preferably be an SC or modified SC cut. 
> 
> This is for a high stability part. The list does keep going on for a while, 
> but that should 
> give you a pretty good idea. 
> 
> Bob
> 
>> On Mar 15, 2017, at 3:11 AM, Gilles Clement  
>> wrote:
>> 
>> Hi, 
>> So what is the « best » design for DIY a high stability OCVXO ? 
>> I am looking after one, needed for an exotic frequency : 5184kHZ 
>> Thx, 
>> Gilles. 
>> 
>> 
>>> Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist  a 
>>> écrit :
>>> 
>>> 
>>> 
>>> On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
>>> 
 
 Looking at oscillator circuits like the HP10811A will give some idea of 
 some of the additional complexity required for a overtone operation. 
 Dissecting a few ocxos may also be helpful. Some start with a 10MHz 
 crystal and a Colpitts sustaining stage and use a 74HC74 or similar to  
 divide the 10Mhz by 2 and drive the output pin. Even when a sinewave 
 output is required often a CMOS inverter drives the output pin via an LC 
 filter.
 
 Bruce
 
>>> 
>>> I don't agree here.  The 10811 is not a good tutorial for general 
>>> oscillator design.  Because it is SC cut, it has a complicated
>>> mode suppression network across the base emitter junction to
>>> suppress mode B as well as the fundamental.
>>> 
>>> The E1983A oscillator uses the same crystal (in a low profile
>>> package).  You can read my paper about it and see that I
>>> used a very simple bridged tee oscillator circuit.  That is
>>> all you need to select the right overtone and mode.
>>> 
>>> This is the same circuit that I used at Zeta Labs 40 years
>>> ago to design hundreds of custom VCXO's, up to the 9th
>>> overtone.  It simply worked every time, unlike various other
>>> designs that were in use at Zeta.
>>> 
>>> Around 1985, I got a consulting gig at Equatorial Communications
>>> to redesign their 5th overtone VCXO.  Only about half of the
>>> crystals would work in their circuit.  They had thousands
>>> of "reject" crystals.  I just used my old Zeta circuit and
>>> all the crystals started working again.
>>> 
>>> Equatorial owned the 10 meter dish that you used to see on
>>> your right going south on 237 just before passing over
>>> Central Expressway in Mountain View.
>>> 
>>> Rick N6RK
>>> 
>>> 
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to 
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> 
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>> and follow the instructions there.
> 
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Re: [time-nuts] Bye-Bye Crystals

[Magnus Danielson]

On 03/15/2017 05:30 PM, Richard (Rick) Karlquist wrote:



On 3/15/2017 4:45 AM, Bob Camp wrote:

Hi

Where do you plan on getting an OCXO grade crystal at an odd frequency
like
that? Much of the performance of a good OCXO is in the crystal. Doing
a proper
design on one is a lot of work. You *might* think that having a design
for 5.00
MHz would give you a good design for 5.50 MHz. I have empirical
evidence that
this isn’t the case. Many years later, I’m still utterly amazed that
this is the way things
work in the crystal business ….( = it’s not just a design issue, it’s
also a business decision)



Some 30 years ago when GPS was in its infancy, the hardware utilized
OCXO's at 10.23 MHz.  Somehow, HP got suckered into trying to make
modified 10811's that ran at that frequency vs 10 MHz.  Jack Kusters
tried to explain to anyone who would listen that this was a major
redesign of the crystal, because he would have to deal with a new
set of anharmonic spurious modes.  Although only a 2.3% frequency
change, everything is different.  In terms of business decisions,
only something with as much "juice" as GPS could have gotten Jack
to make a custom frequency.  As it turned out, a few dozen crystals
were made, and that was the end of it.  I managed to snag them
before they were thrown out, in case they might be useful for
something.

The original poster wanted not only an odd frequency (which I don't
recommend for the reasons above) but also wanted to varactor tune
the oscillator.  I also don't recommend doing that because of the
difficulty of generating a clean enough DC voltage.  Against my
advice, the HP smart clocks were tuned with DAC's driving varactors.
They never really got that to work up to their expectations.
Synthesis is so advanced now, 20 years later, that there is
no reason IMHO to voltage tune an OXCO.


Agree. Synthesis chips is cheap now and should be sufficiently good.

Also, it may not be a good strategy to zero-beat to the carrier, so such 
a frequency may actually be a bad choice. Modern DDS chips allows the 
tuning of the LO1 such that different IF frequencies can be tried.


For instance, the RTL-SDR is typically operated in 0 Hz beat, such that 
the front-end mixes down to 0 Hz for the carrier and lets the RTL chip 
sample the signal. This causes a distinct "blimp" from the 1/f noise.
Shifting the IF from 0 Hz and then let the RTL downconvert after 
sampling removes this blimp since the 1/f noise can be brought out of 
spectrum. When I dug around, this was available as an option even in GNU 
Radio if you only knew it.


This just to illustrate that best result is not always achieved by 
bringing it straight on carrier. Sure, it makes the design very very 
simple, but has its drawbacks.


Now, the 164 kHz carrier, as sampled by a 48 kHz clock produces a 20 kHz 
beat frequency as it wrapps down in the undersampling. To digitally 
convert it to DC or lock straight to 20 kHz digitally is fairly trivial.


Similarly, a typical GPS receiver often has the digitized signal offset.

With a more modern view on receiver design and considering the synthesis 
tools available, you can play around quite easily and move things around 
in interesting ways. For instance, consider that you have an IF filter, 
you can with some care sweep the filter and "tune" the LOs to the IF 
frequency working best for your needs. We do that in ham receivers to 
shift filtering to where it helps from nearby strong signals.


Cheers,
Magnus
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Re: [time-nuts] Bye-Bye Crystals

[Richard (Rick) Karlquist]

On 3/15/2017 4:45 AM, Bob Camp wrote:

Hi

Where do you plan on getting an OCXO grade crystal at an odd frequency like
that? Much of the performance of a good OCXO is in the crystal. Doing a proper
design on one is a lot of work. You *might* think that having a design for 
5.00
MHz would give you a good design for 5.50 MHz. I have empirical evidence 
that
this isn’t the case. Many years later, I’m still utterly amazed that this is 
the way things
work in the crystal business ….( = it’s not just a design issue, it’s also a 
business decision)



Some 30 years ago when GPS was in its infancy, the hardware utilized
OCXO's at 10.23 MHz.  Somehow, HP got suckered into trying to make
modified 10811's that ran at that frequency vs 10 MHz.  Jack Kusters
tried to explain to anyone who would listen that this was a major
redesign of the crystal, because he would have to deal with a new
set of anharmonic spurious modes.  Although only a 2.3% frequency 
change, everything is different.  In terms of business decisions,

only something with as much "juice" as GPS could have gotten Jack
to make a custom frequency.  As it turned out, a few dozen crystals
were made, and that was the end of it.  I managed to snag them
before they were thrown out, in case they might be useful for
something.

The original poster wanted not only an odd frequency (which I don't
recommend for the reasons above) but also wanted to varactor tune
the oscillator.  I also don't recommend doing that because of the
difficulty of generating a clean enough DC voltage.  Against my
advice, the HP smart clocks were tuned with DAC's driving varactors.
They never really got that to work up to their expectations.
Synthesis is so advanced now, 20 years later, that there is
no reason IMHO to voltage tune an OXCO.

Rick
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Re: [time-nuts] Bye-Bye Crystals

[Mike Cook]

> Le 15 mars 2017 à 08:11, Gilles Clement  a écrit :
> 
> Hi, 
> So what is the « best » design for DIY a high stability OCVXO ? 
> I am looking after one, needed for an exotic frequency : 5184kHZ 

Crystals have existed for this frequency. A quick scan of the bay threw up item 
252813375636 which is an old radio crystal. If you can figure what you need to 
drive it, it could be installed into a home-brew oven. How stable you can get 
it would be the subject of a nice project.


> Thx, 
> Gilles. 
> 
> 
>> Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist  a 
>> écrit :
>> 
>> 
>> 
>> On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
>> 
>>> 
>>> Looking at oscillator circuits like the HP10811A will give some idea of 
>>> some of the additional complexity required for a overtone operation. 
>>> Dissecting a few ocxos may also be helpful. Some start with a 10MHz crystal 
>>> and a Colpitts sustaining stage and use a 74HC74 or similar to  divide the 
>>> 10Mhz by 2 and drive the output pin. Even when a sinewave output is 
>>> required often a CMOS inverter drives the output pin via an LC filter.
>>> 
>>> Bruce
>>> 
>> 
>> I don't agree here.  The 10811 is not a good tutorial for general oscillator 
>> design.  Because it is SC cut, it has a complicated
>> mode suppression network across the base emitter junction to
>> suppress mode B as well as the fundamental.
>> 
>> The E1983A oscillator uses the same crystal (in a low profile
>> package).  You can read my paper about it and see that I
>> used a very simple bridged tee oscillator circuit.  That is
>> all you need to select the right overtone and mode.
>> 
>> This is the same circuit that I used at Zeta Labs 40 years
>> ago to design hundreds of custom VCXO's, up to the 9th
>> overtone.  It simply worked every time, unlike various other
>> designs that were in use at Zeta.
>> 
>> Around 1985, I got a consulting gig at Equatorial Communications
>> to redesign their 5th overtone VCXO.  Only about half of the
>> crystals would work in their circuit.  They had thousands
>> of "reject" crystals.  I just used my old Zeta circuit and
>> all the crystals started working again.
>> 
>> Equatorial owned the 10 meter dish that you used to see on
>> your right going south on 237 just before passing over
>> Central Expressway in Mountain View.
>> 
>> Rick N6RK
>> 
>> 
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> 
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"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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Re: [time-nuts] Bye-Bye Crystals

[Bob Camp]

Hi

Where do you plan on getting an OCXO grade crystal at an odd frequency like 
that? Much of the performance of a good OCXO is in the crystal. Doing a proper 
design on one is a lot of work. You *might* think that having a design for 
5.00
MHz would give you a good design for 5.50 MHz. I have empirical evidence 
that
this isn’t the case. Many years later, I’m still utterly amazed that this is 
the way things
work in the crystal business ….( = it’s not just a design issue, it’s also a 
business decision) 

More or less the crystal needs to be:

1) Cut specifically to have a turn at a temperature that makes sense for your 
application.
2) A “large blank” design (for it’s frequency)
3) In a cold weld package (most of the normal crystals are resistance weld)
4) Run through a high vacuum / high temperature process
5) Be plated with gold rather than something like silver or aluminum (unless 
it’s at VHF).
6) Have a motional capacitance that makes sense for your EFC range ( normally = 
minimize)
7) Preferably be an SC or modified SC cut. 

This is for a high stability part. The list does keep going on for a while, but 
that should 
give you a pretty good idea. 

Bob

> On Mar 15, 2017, at 3:11 AM, Gilles Clement  wrote:
> 
> Hi, 
> So what is the « best » design for DIY a high stability OCVXO ? 
> I am looking after one, needed for an exotic frequency : 5184kHZ 
> Thx, 
> Gilles. 
> 
> 
>> Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist  a 
>> écrit :
>> 
>> 
>> 
>> On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
>> 
>>> 
>>> Looking at oscillator circuits like the HP10811A will give some idea of 
>>> some of the additional complexity required for a overtone operation. 
>>> Dissecting a few ocxos may also be helpful. Some start with a 10MHz crystal 
>>> and a Colpitts sustaining stage and use a 74HC74 or similar to  divide the 
>>> 10Mhz by 2 and drive the output pin. Even when a sinewave output is 
>>> required often a CMOS inverter drives the output pin via an LC filter.
>>> 
>>> Bruce
>>> 
>> 
>> I don't agree here.  The 10811 is not a good tutorial for general oscillator 
>> design.  Because it is SC cut, it has a complicated
>> mode suppression network across the base emitter junction to
>> suppress mode B as well as the fundamental.
>> 
>> The E1983A oscillator uses the same crystal (in a low profile
>> package).  You can read my paper about it and see that I
>> used a very simple bridged tee oscillator circuit.  That is
>> all you need to select the right overtone and mode.
>> 
>> This is the same circuit that I used at Zeta Labs 40 years
>> ago to design hundreds of custom VCXO's, up to the 9th
>> overtone.  It simply worked every time, unlike various other
>> designs that were in use at Zeta.
>> 
>> Around 1985, I got a consulting gig at Equatorial Communications
>> to redesign their 5th overtone VCXO.  Only about half of the
>> crystals would work in their circuit.  They had thousands
>> of "reject" crystals.  I just used my old Zeta circuit and
>> all the crystals started working again.
>> 
>> Equatorial owned the 10 meter dish that you used to see on
>> your right going south on 237 just before passing over
>> Central Expressway in Mountain View.
>> 
>> Rick N6RK
>> 
>> 
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>> and follow the instructions there.
> 
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Re: [time-nuts] Bye-Bye Crystals

[Gilles Clement]

Hi, 
So what is the « best » design for DIY a high stability OCVXO ? 
I am looking after one, needed for an exotic frequency : 5184kHZ 
Thx, 
Gilles. 


> Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist  a 
> écrit :
> 
> 
> 
> On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
> 
>> 
>> Looking at oscillator circuits like the HP10811A will give some idea of some 
>> of the additional complexity required for a overtone operation. Dissecting a 
>> few ocxos may also be helpful. Some start with a 10MHz crystal and a 
>> Colpitts sustaining stage and use a 74HC74 or similar to  divide the 10Mhz 
>> by 2 and drive the output pin. Even when a sinewave output is required often 
>> a CMOS inverter drives the output pin via an LC filter.
>> 
>> Bruce
>> 
> 
> I don't agree here.  The 10811 is not a good tutorial for general oscillator 
> design.  Because it is SC cut, it has a complicated
> mode suppression network across the base emitter junction to
> suppress mode B as well as the fundamental.
> 
> The E1983A oscillator uses the same crystal (in a low profile
> package).  You can read my paper about it and see that I
> used a very simple bridged tee oscillator circuit.  That is
> all you need to select the right overtone and mode.
> 
> This is the same circuit that I used at Zeta Labs 40 years
> ago to design hundreds of custom VCXO's, up to the 9th
> overtone.  It simply worked every time, unlike various other
> designs that were in use at Zeta.
> 
> Around 1985, I got a consulting gig at Equatorial Communications
> to redesign their 5th overtone VCXO.  Only about half of the
> crystals would work in their circuit.  They had thousands
> of "reject" crystals.  I just used my old Zeta circuit and
> all the crystals started working again.
> 
> Equatorial owned the 10 meter dish that you used to see on
> your right going south on 237 just before passing over
> Central Expressway in Mountain View.
> 
> Rick N6RK
> 
> 
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Re: [time-nuts] WTB: GPSDO

[Attila Kinali]

On Tue, 14 Mar 2017 21:25:19 -0700
Chris Albertson  wrote:

> You can also verify the GPSDO is working correctly by looking at the
> EFC voltage.  That is the control signal the controller sends to that
> $25 eBay crystal.  You'd expect that the ESFC volts follows some kind
> of theory and tracks the environment and you'd not expect a random

This depends very much on the oscillator used. If it's a good OCXO,
you will see hardly any influence from environment and the EFC will
be dominated by GPS noise at short time scales and aging of the OCXO
at long time scales. Have a look at what TvB reported in November[1,2]
on the measurement of a bunch of Thunderbolts(free running). Yes, there
is something that seems to be environmental effects for some oscillators
at some time scales. Figuring out where you actually see such effects
will need some serious statistical skills. IMHO it's much easier to just
get a known-good GPSDO and a rubidium for verification.


Attila Kinali



[1] https://www.febo.com/pipermail/time-nuts/2016-November/101913.html
[2] https://www.febo.com/pipermail/time-nuts/2016-November/101939.html

-- 
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] Bye-Bye Crystals

[Bruce Griffiths]

Gilles

What is the required tuning range for the OCVXO?

Bruce

> 
> On 15 March 2017 at 20:11 Gilles Clement  
> wrote:
> 
> Hi,
> So what is the « best » design for DIY a high stability OCVXO ?
> I am looking after one, needed for an exotic frequency : 5184kHZ
> Thx,
> Gilles.
> 
> > > 
> > Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist 
> >  a écrit :
> > 
> > On 3/14/2017 4:03 AM, Bruce Griffiths wrote:
> > 
> > > > > 
> > > Looking at oscillator circuits like the HP10811A will give 
> > > some idea of some of the additional complexity required for a overtone 
> > > operation. Dissecting a few ocxos may also be helpful. Some start with a 
> > > 10MHz crystal and a Colpitts sustaining stage and use a 74HC74 or similar 
> > > to divide the 10Mhz by 2 and drive the output pin. Even when a sinewave 
> > > output is required often a CMOS inverter drives the output pin via an LC 
> > > filter.
> > > 
> > > Bruce
> > > 
> > > > > 
> > I don't agree here. The 10811 is not a good tutorial for general 
> > oscillator design. Because it is SC cut, it has a complicated
> > mode suppression network across the base emitter junction to
> > suppress mode B as well as the fundamental.
> > 
> > The E1983A oscillator uses the same crystal (in a low profile
> > package). You can read my paper about it and see that I
> > used a very simple bridged tee oscillator circuit. That is
> > all you need to select the right overtone and mode.
> > 
> > This is the same circuit that I used at Zeta Labs 40 years
> > ago to design hundreds of custom VCXO's, up to the 9th
> > overtone. It simply worked every time, unlike various other
> > designs that were in use at Zeta.
> > 
> > Around 1985, I got a consulting gig at Equatorial Communications
> > to redesign their 5th overtone VCXO. Only about half of the
> > crystals would work in their circuit. They had thousands
> > of "reject" crystals. I just used my old Zeta circuit and
> > all the crystals started working again.
> > 
> > Equatorial owned the 10 meter dish that you used to see on
> > your right going south on 237 just before passing over
> > Central Expressway in Mountain View.
> > 
> > Rick N6RK
> > 
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to 
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> > 
> > > 
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Re: [time-nuts] WTB: GPSDO

[Chris Albertson]

Yes, that is a problem.  How to test a 10 MHz oscillator of any kind
(GPSDO or not) if you only have one oscillator.

I call it the "bootstrap problem"  and I think it's worth some
discussion.  The easy way is to buy a few known good clocks before you
set out to make a clock but that is the "easy way".   that

It is not hard to test its long term stability.  Simply count how may
cycles your new device makes in (say) 10 seconds.   Now all you need
is a way to measure 10 seconds.GPS receivers are good at this.
For short term stability you have yo have some faith.  Buy a $25
oversized crystal oscillator that was made by the name brand with a
decent reputation and it will likely be reasonable

All the GPSDO does is adjust the electronic frequency control of that
$25 eBay oscillator until there are EXACTLY 10,000,000 counts between
every 1 Hz pulse.   The GPSDO is self testing.  Every second it
decides if that $25 crystal is running to fast or to slow and then
does something.   One of the things it should do it tell its owner if
the crystal is reusing much to fast or slow or if it is just right.
You will know the GPSDO has decent long term stability because the
green :just right" LED stays on all the time.

You can also verify the GPSDO is working correctly by looking at the
EFC voltage.  That is the control signal the controller sends to that
$25 eBay crystal.  You'd expect that the ESFC volts follows some kind
of theory and tracks the environment and you'd not expect a random

In short you can verify the correct operation of a home build GPSDO
because you can see inside of it.  When you see the inside parts are
working as expected you can have high confidence it is all working
well. But for proof you need at least to more known-good
oscillators and you can measure beat frequencies between them.



On Tue, Mar 14, 2017 at 3:33 PM, Tim Lister  wrote:
> On Fri, Mar 10, 2017 at 2:35 PM, Chris Albertson
>  wrote:
>> A GPSDO is not hard to make.  All you need is some way to compare the
>> phase of two signals, an XOR gate can do that.  Then a small $2
>> process moves the control voltage on the crystal.I tried one to
>> build the simplest GPSDO that could still work.   Got the parts count
>> down to about four or five and the cost well under $10 plus the OXO
>> which was about $20.  The simplest dumb one I could make keeps about
>> e-10.  Not great but enough for many uses.   I compared to my
>> Thunderbolt and I could see the phase advance and retreat.  Just a
>> little most sophistication and I likely could do much better but my
>> goal was to prove to myself that a GPSDO could be build VERY simply
>> with cheap parts
>>
>
> Hi Chris, that's good news that a GPSDO is that easy to make (at least
> a basic one) as that is exactly my medium term plan ! The issue of
> course is having something to test the newly built GPSDO against... I
> got one of the rehoused Trimble UCCM-based GPSDOs off ebay a while ago
> but haven't been super happy with it. It's quite a bit less sensitive
> than more modern GPS receivers and it often struggles to get even 1
> satellite with the indoor patch antenna. At one point both red alarm
> LEDs came on and stayed on despite power cycles - I eventually fixed
> that by taking it apart and finding and hitting a reset button on the
> board. Currently although I can talk to the unit over serial and it
> seems to respond, Lady Heather is not seeing any output from it.
>
> Combined these things don't give me a great deal of confidence that
> this unit will act as a stable master reference. I was wondering if a
> second GPSDO like Russ linked to would work better (I have a ublox
> LEA-6T GPS already which I plan to use as the basis of the homebuilt
> GPSDO and it consistently sees many more satellites than the UCCM
> with a similar indoor antenna)  or put the money to getting an outdoor
> antenna mounted (don't feel happy drilling holes in the house myself)
> by someone. Do 2 GPSDOs tell you much more or just that each is
> different and you need a third to adjudicate ? (I can see a slippery
> slope looming from here...)
>
> Cheers,
> Tim
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-- 

Chris Albertson
Redondo Beach, California
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