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
>> 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
>> A microprocessor controlled XO system allows for using cheap crystals
>> 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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