[time-nuts] Z3805 incident

Bob Camp lists at rtty.us
Fri Nov 30 02:06:24 UTC 2012


HI

Some simple empirical data:

1) Jumps tend to get further apart as the oscillator ages.
2) AT's have larger jumps than SC's.
3) A typical SC jump is below 1x10^-9 
4) It's not a lot of things (spurs, drive, temperature, load,stress, micro-fractures, plating defects) if you need to explain all cases = they don't explain all events
5) It can be a lot of things (spurs, drive, temperature, load, stress, micro-fractures, plating defects) in some cases = they do explain some events

The first published data I have seen on jumps is in a Fairchild Semiconductor App note from the late 60's / early 70's. They built a JFET based oscillator and it jumped….

Bob

On Nov 29, 2012, at 7:30 PM, Volker Esper <ailer2 at t-online.de> wrote:

> ...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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> 
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