[time-nuts] Z3805 incident

[Volker Esper]

...imho it has indeed jumped back, see the picture of 1643 GMT today. 
You recognize the peak down yesterday at about 1900 GMT, then a smaller 
peak up at about 2300 GMT and - after having a troubled night - again a 
peak up. The EFC voltage now is nearly the same as prior to the "impact 
series". I suppose it's actually a "crystal jump".

In 1997 HP wrote in it's AN 200-2 (Fundamentals of Quartz Oscillators): 
"...Crystals having unwanted signals could also shift from one resonate 
point to another producing a frequency jump which would be an 
undesirable effect."

IEEE has some experience with that phenomenon, too. An article from 1996 
can be found in their Digital Library

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=559877&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel3%2F4090%2F12100%2F00559877.pdf%3Farnumber%3D559877

wich deals with that issue:

"In this paper recently classified intermittent and discrete frequency 
jump phenomena are briefly reviewed and currently not well understood 
abrupt frequency jump phenomena are analysed and discussed in detail."

John R. Vig writes in his "Quartz Crystal Resonators and
Oscillators For Frequency Control and Timing Applications - A Tutorial"
(2004):

"It is the changes in the stresses, and the changes produced by the 
stresses that cause frequency instabilities. There exists evidence that, 
on a microscopic level, stress relief is not a continuous process. It 
can occur in bursts that can, possibly, contribute to noise and 
frequency jumps."

Numerous articles discuss the effects of contamination and failures of 
the crystal clamp that obviously contribute to the phenomenon.

Though very interesting stuff, that all sounds kind of academical to me. 
Now I know it could be possible, that my GPSDO suffers from that cause. 
However, since I don't know if or when or how often the effect recurs, I 
am the one, who has broken nights now...

I'll keep a jealous watch over the diagrams...

Volker






Am 30.11.2012 00:14, schrieb Dennis Ferguson:
>
> On 29 Nov, 2012, at 02:32 , Charles P. Steinmetz<charles_steinmetz at lavabit.com>  wrote:
>
>>> This is a classic crystal jump. The crystal changed its frequency magically from one second to the next and the software compensated for it
>>
>> Here is another example of a 3805 having a bad moment.  For just about two minutes, it reported a phase jump of nearly 3 uS and then immediately fell back nearly to its previous baseline, settling to the baseline in about an hour and not requiring any longer-term change of the EFC voltage.  This does not look like a typical crystal frequency shift to me, but I cannot rule that out.  It looks more like what I'd expect to see if I set the cable delay to 3 uS for 2 minutes, then back to 0.
>
> I think I would be more likely to call this one, where the crystal jumps
> to another frequency for a while and then jumps back to about what it was,
> a "classic crystal jump".  I've seen this before, though not as large as the
> change you show.  I hear these raise hell when they try to use PTP to transmit
> telecom-quality timing over asynchronous ethernet because it is hard to run
> a PTP control loop tight enough (i.e. at a high enough data rate) to correct
> that before it does damage.
>
> I think the other problem, with the crystal jumping to another frequency and
> apparently staying there (I'm assuming it hasn't jumped back), could have a
> broader range of causes.
>
> Dennis Ferguson
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