[time-nuts] Re: Custom Quartz crystals

[Bob kb8tq]

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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