[time-nuts] oscillators

[Bob Camp]

Hi

The fundamental / third approach is one of several possible ways to go. You
can also run an SC on the B and C modes to get thermometer data. Early
implementations used a pair of independent blanks, one cut to be a good
thermometer. Some have even gone as far as to mount a thermistor on the
crystal.

No matter what you do, it adds cost.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Jim Lux
Sent: Thursday, August 30, 2012 8:55 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] oscillators

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.


_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.