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

[Magnus Danielson]

Hi,

Well, actually you steer back to the right frequency... but do not 
compensate for the frequency deviation you experienced. So the net 
effect will be a subtle frequency shift as a side-consequence. This is 
similar to how ovens react too on temperature-shift. This also has 
consequence for the phase, which the effect is easiest measured. I've 
measured similar effect on a particuarly badly made lock-up design.

Cheers,
Magnus

On 2022-09-06 05:56, Bob kb8tq via time-nuts wrote:
> 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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