[time-nuts] Question on crystal jumps

[Neville Michie]

Hi,
The EFRATOM LPRO does not use a OCXO, just a straight quartz crystal  
oscillator.
The control voltage swings around a volt as the base plate warms up.
The time constant of the PLL that the XO is in must be quite short, a  
small fraction of a second
so that the effect of drifting temperature has little effect on the  
output.
I guess that all the crystal does is to filter what must be a quite  
noisy signal
from the atomic resonance. When I inspected the circuit board I could  
not even find the crystal,
it is not in a grand crystal can.
cheers, Neville Michie


On 23/10/2008, at 9:42 PM, WB6BNQ wrote:

> Hi Bob Q,
>
> Yes Rubidium (Rb) and Cesium (Cs) standards use OCXO's.
>
> I suppose the way to look at it is the Rb or Cs chamber acts as an
> invariant
> atomic filter with extremely narrow bandpass (i.e., with an extremely
> high Q).
> The resonant frequencies of these atomic filters are up in the  
> microwave
> regions
> and thus do not lend themselves easily to direct comparison.  So, a  
> high
> quality
> standard frequency oscillator is locked in a loop controlled by the
> atomic
> filter.  The OCXO's output is the reference signal out of the atomic
> standard.
>
> I hope this rather simplistic overview answers your question ?
>
> Bill....WB6BNQ
>
> Bob Q wrote:
>
>> Do rubidium standards use an OCXO?
>> Bob Q.
>>
>> ----- Original Message -----
>> From: "Rick Karlquist" <richard at karlquist.com>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Sent: Wednesday, October 22, 2008 2:23 PM
>> Subject: Re: [time-nuts] Question on crystal jumps
>>
>>> I'm not quite sure what the question is here, but when
>>> we made 10811 oscillators at HP, "jumps happened".  Some
>>> crystals were better than others, but no crystal was immune
>>> from jumps.  With good quality crystals, you might be able
>>> to put an upper bound on the magnitude of jumps, like 10-9,
>>> but not on the time between jumps.  I also noticed that there
>>> didn't seem to be any correlation between jump activity
>>> and stability between jumps.  You could have an oscillator
>>> with really low aging, say a few parts in 1E11 per day that
>>> looked really good for quite a while, but then the frequency
>>> jumps.  After you've controlled everything you can about the
>>> crystal process, the electronics, the oven and the environment,
>>> you are still left with jumps.  If you want no jumps, go to
>>> an atomic standard like rubidium.  There are mechanisms that
>>> can cause jumps in rubidium standards as well, but good
>>> rubidium standards don't jump.
>>>
>>> Rick Karlquist N6RK
>>>
>>>
>>> iovane\@inwind\.it wrote:
>>>> I would be very pleased to know when (date and time) anybody
>>>> out there happened to record jumps in frequency of crystals.
>>>> I have stable (e-07) tuning forks which happen to jump too,
>>>> and I don't understand why, even having under control
>>>> temperature and air pressure. Sometimes they return to their
>>>> prior frequency with another jump, and this could happen even
>>>> days later, sometimes they jump and then recover smoothly the
>>>> prior frequency in a short time (such as one hour).
>>>> I have no idea whether any correlations would exist between
>>>> crystals and tuning forks jumps, regarding the causes that
>>>> could trigger metastability, and hence I would have a look at
>>>> crystal data in order to improve the base for future
>>>> speculation.
>>>>
>>>> Thanks in advance.
>>>> Antonio I8IOV
>>>>
>>>>
>>>>
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>>>
>>>
>>>
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