[time-nuts] Re: Custom Quartz crystals-> measurement

[Bernd Neubig]

The attached survey of the classical IEC 60444-2 "phase zero"  measurement technique based on the PI-network described in IEC60444-1 vs. the modern error corrected measurement method of  IEC 60444-5 may provide a helpful inside into the measurement techniques for quartz crystals. 

More can be found at https://www.axtal.com/English/Support/TechnicalArticlesPublications/LiteratureaboutQuartzCrystals/


Bernd

-----Ursprüngliche Nachricht-----
Von: Bob kb8tq via time-nuts [mailto:time-nuts at lists.febo.com] 
Gesendet: Samstag, 20. August 2022 05:20
An: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Brooke Clarke <brooke at pacific.net>; Bob kb8tq <kb8tq at n1k.org>
Betreff: [time-nuts] Re: Custom Quartz crystals

Hi

In the era that the fixture was used, doing this with an network analyzer wasn’t even a pipe dream. Doing up an adequate set of data with the gear of that era was a long and drawn out process. 
Getting a measurement with a simple fixture was a second or two. 

Indeed if 1% on resistance and a tenth of a ppm frequency wasn’t adequate, you might head off to other approaches. Given the make tolerances on the crystals, neither one was a limit to production testing. 

The biggest limit in reality was the accuracy of the load capacitor. 
That’s why you never / ever swapped it out. The value that was in there was confirmed by some non-trivially exciting testing with a number of “golden” crystals. 

Bob

> On Aug 19, 2022, at 10:30 AM, Brooke Clarke via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi:
> 
> IEC 444 is a PI-Netowrk measurement method for crystals.  It is supposed to me more accurate than the method that uses a physical CL.
> The HP 41900A has the look and feel of the linked PI-Network fixture so may just be a re-branded version.
> https://prc68.com/I/4395A.shtml#E5100
> 
> --
> Have Fun,
> 
> Brooke Clarke
> https://www.PRC68.com
> axioms:
> 1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
> 2. Everybody, with no exceptions, holds false beliefs.
> 
> -------- Original Message --------
>> Hi
>> 
>> Thanks to a bit of off list coaching from those who’s memory 
>> (obviously) better than mine :) :
>> 
>> This is the magic test set that Motorola (and many others) got pretty 
>> heavily into:
>> 
>> https://isolalab.com/pinetwork.html 
>> <https://isolalab.com/pinetwork.html>
>> 
>> The gizmo is right at the top of the page. There’s a nice paragraph 
>> next to it and a diagram of what’s inside.
>> 
>> The original outfit that made it ( Cathodeon / Pye ) has been out of 
>> business for quite a while. They apparently made the fixture to 
>> support their crystal manufacturing business. Just how many fixtures 
>> they sold to their competitors …. no idea.
>> 
>> Bob
>> 
>>> On Aug 17, 2022, at 8:17 AM, Bob kb8tq <kb8tq at n1k.org> wrote:
>>> 
>>> Hi
>>> 
>>> One “interesting” way to look at this is a “delta F” test.
>>> It’s based on a system that (essentially) always measures things at 
>>> series. You put the (maybe) 20 pf  load cap in series with the 
>>> crystal and zip off it goes to measure the net result of the crystal 
>>> at a 20 pf load.
>>> 
>>> Typically you did this by pushing a paddle on a fixture. Yes that’s 
>>> very specific to one rig up. Turns out that Motorola decided it was 
>>> a fun thing and we tested a *lot* of crystals that way. It’s been “a 
>>> while” … but .. fundamental crystals came in at > 400 ppm. Third 
>>> overtones might be around
>>> 30 ppm. Fifth overtones might be around 3 to 5 ppm.
>>> 
>>> No this isn’t for the same crystal or even the same crystal package. 
>>> It also isn’t for SC cuts, these all where AT’s.
>>> 
>>> … and yes, if I could remember the name if the UK outfit that made 
>>> the test heads, I’d give them credit for their cute little gizmo.
>>> 
>>> One interesting outcome of testing this way was to spec crystals as 
>>> some number of PPM off series rather than with a load. Changing the 
>>> load cap in the fixture was “not done”.  AFIK that was very specific 
>>> to internal Motorola documents. The only time I saw it used 
>>> elsewhere was on crystals that operated below series.
>>> 
>>> Bob
>>> 
>>>> On Aug 17, 2022, at 5:28 AM, Richard (Rick) Karlquist via time-nuts <time-nuts at lists.febo.com> wrote:
>>>> 
>>>> It is hard to answer your question.  The tuning range depends on 
>>>> the varactor(s) used in the respective oscillators, and the range 
>>>> of the tuning voltages.
>>>> I think I could roughly say from memory that putting in a crystal 
>>>> meant for the other oscillator would probably result in not being 
>>>> able to reach 10.000000 MHz.  Or just barely reaching it and having 
>>>> no aging margin.  I had to apply a lot of arm twisting to Jack 
>>>> Kusters to get him to make the series resonant (at 10 MHz) 
>>>> crystals.  I made sure that this was really necessary before going 
>>>> to war on it.
>>>> 
>>>> Rick N6RK
>>>> 
>>>> On 8/14/2022 3:35 PM, Hal Murray via time-nuts wrote:
>>>>> Richard (Rick) Karlquist said:
>>>>>> We actually used the upper turnover because the E1938 had to 
>>>>>> operate at ambient up 85  degrees.  BTW, the E1938 crystals had 
>>>>>> to be calibrated for
>>>>>> 10.000000 MHz at series resonance, unlike the 10811 crystals 
>>>>>> which were calibrated for 20 pF (IIRC).
>>>>> How big is the difference between series and 20pF compared to the tuning range?
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