[time-nuts] oscillators

Jim Lux jimlux at earthlink.net
Thu Aug 30 08:54:40 EDT 2012


On 8/29/12 8:45 PM, Richard (Rick) Karlquist wrote:
>
> On 8/27/2012 11:45 PM, WB6BNQ wrote:
>>
>>
>> A microprocessor controlled XO is a non oven crystal oscillator system
>> that has
>> additional computational control providing a bit more than just mere
>> passive
>> temperature compensation.  The additional computational capability
>> deals with
>> having coefficients of that particular oscillator's behavior pre coded to
>> compensate for the nonlinear behavior over a given temperature rang
>
> It doesn't use coefficients.  It has a look up table of frequency vs
> temperature.
>
>>
>> A microprocessor controlled XO system allows for using cheap crystals
>> with
>> minimum processing time and costs.  Because of limited storage space
>> there is no
>
> No it doesn't use a cheap crystal.  It uses a *special* SC cut crystal.
> This crystal could very easily cost more than an OCXO crystal.
>

Isn't the crystal cut (and the circuit designed) in such a way that it 
supports both the fundamental and the third overtone simultaneously, and 
comparing the frequencies of the two (or, more accurately, fF- fthird/3) 
is how they measure the temperature, which is then used to look up the 
correction factor in a PROM.





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