Hi 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.
Bob > On Nov 1, 2017, at 4:38 PM, Hal Murray <[email protected]> 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. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
