[time-nuts] Oscillators and Ovens

Bob kb8tq kb8tq at n1k.org
Wed Nov 1 18:13:04 EDT 2017


A high Q crystal by design is very difficult to tune. Putting it in a circuit that will 
swing it far enough to compensate it degrades the Q. In addition, thermal noise
will come into the compensation circuit (even if it is noise free) and degrade things. 


> On Nov 1, 2017, at 4:38 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>> In general, OCXOs have crystals with high Q -> low phase noise,  especially
>> compared to a TCXO, which *can't* have high Q, or the  temperature
>> compensation circuit can't do it's work. 
> I don't understand that.  Why can't I build a high Q TCXO?  I don't need to 
> change the compensation very fast.  Are good crystals high enough Q that it 
> would take too long?
> What's the time constant?  I'd guess it's Q/freq, maybe with factors of 2pi 
> or e or ???
> That seems small relative to how fast temperature changes.  (but maybe fast 
> relative to FCC smearing or things like that)
> -- 
> These are my opinions.  I hate spam.
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