[time-nuts] Re: Do crystals still jump?

[Bob kb8tq]

Hi

With an atomic clock, the crystal oscillator is locked ( FLL or PLL ) to
the atomic resonance. The OCXO is simply a circuit element rather than 
the thing that determines the output. If the OCXO “jumps” then the PLL
or FLL gets it back on frequency ( quickly ….) . Net result is that you 
don’t see a jump, you see a spike. 

Bob

> On Sep 5, 2022, at 6:26 PM, ed breya via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Rick wrote:
> 
> "I just wanted to clarify that crystals are quite capable of
> jumping without any help from temperature shifts.  The E1938A
> proved this.  With a thermal gain in the hundreds of thousands,
> the crystal temperature never budged.  Yet the crystals (which
> were essentially the same as what was in the 10811) did jump;
> every one of them from time to time.  There were no crystals
> that "never" jumped, depending on how you define "jump".
> A crystal might appear not to jump for while, but if observed
> long enough you would always see a jump sooner or later.
> It wasn't like you could sort them for "non-jumping" units.
> 
> The situation reminded me of the so called "smart clock"
> concept, where the clock would "learn" what its aging was
> and then compensate it out during hold over.  The trouble
> with this was that the aging curves have "knees" in them
> and you are hoping that a knee doesn't occur during holdover.
> 
> With the advent of small, low power, affordable atomic frequency
> sources, we now have a way to get rid of jumps."
> 
> But don't all these atomic frequency sources ultimately (in practice) depend on crystal oscillators anyway, making them subject to the same jump issues?
> 
> 
> Ed
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