[time-nuts] Improving the stability of crystal oscillators

[Don Collie]

Hi Rick,
    Perhaps I should have said : "Temperature at which the lowest change of 
frequency with temperature occurs".
    What cut of crystal is used in these high quality crystal references, 
please?
Cheers,............................................Don C.

----- Original Message ----- 
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: "Don Collie" <donmer at woosh.co.nz>; "Discussion of precise time and 
frequency measurement" <time-nuts at febo.com>
Sent: Tuesday, October 16, 2007 2:54 PM
Subject: Re: [time-nuts] Improving the stability of crystal oscillators


> Don Collie wrote:
>
>>     Yes, you can cut a crystal to have an inversion temp at 25Deg C. 
>> [well certainly with an AT cut - I`m not sure about the SC cut.]
>> Cheers,............................................Don C.
>
> The AT cut has an inflection point at 25 degrees C.  You cannot
> get a "turnover" (which is what I think you mean an "inversion")
> at the inflection point.
>
> As SC cut inventor Jack Kusters explained to me, the "true" SC cut
> has an inflection point temperature of around 85 degrees C.  You can get
> a turnover above or below this, depending on minor angle changes.
> Some crystal fabs make a so called "fake SC" cut where they attempt
> to change the inflection point.  However, when this is done the stress
> compensation is degraded or lost.
>
> Rick Karlquist N6RK
>
>
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