[time-nuts] Oscillators and Ovens
k8yumdoober at gmail.com
Wed Nov 1 18:44:52 EDT 2017
This discussion is getting really interesting. In thinking about the
crystal Q versus
tuning range conundrum, two (presumably-overlapping) concerns come to mind:
1. The motional parameters of a high-Q crystal are such that the external
needed to pull it very far would be wholly impractical.
2. Varactors themselves probably have pretty limited Q over much of their
Is my thinking on the right track at all?
On Wed, Nov 1, 2017 at 5:13 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
> 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
> 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,
> >> 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
> > change the compensation very fast. Are good crystals high enough Q that
> > would take too long?
> > What's the time constant? I'd guess it's Q/freq, maybe with factors of
> > or e or ???
> > That seems small relative to how fast temperature changes. (but maybe
> > relative to FCC smearing or things like that)
> > --
> > These are my opinions. I hate spam.
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