[time-nuts] Super stable BVA Quartz resonators... BVA??

[Bernd T-Online]

Jeff Mock wrote:
> How does crystal aging look on a graph of temp versus frequency....
> What does this graph look like as a crystal ages?  Does the optimal 
> operating temperature change over time, that is, does the graph tend to 
> move left and right, or does aging tend to move the graph vertically 
> (the optimal freq stays the same, but the optimal operating temperature 
> changes as a result of aging).

I can confirm Rick's statement, that there is no noticable effect of 
aging on the turnover temperature (TOT).
Looking at it from physics standpoint, frequncy aging is mainly caused 
by minor changes of vibrating mass  and/or by changes in elastic 
properties (both due to various mechanisms). See my earlier thrad on 
aging mechanisms.
On the other hand, the turn-over temperature is primarily governed by 
the cut angle (in connection with the resonator shape etc.). Mass 
loading, i.e. changes of electrode mass, has also an infuence, but this 
is much weaker. Roughly stated: a change of the TOT by one degC may be 
caused by a variation of the mass loading by an amount eqivalent to a 
frequency change of n*1000 ppm or so. This means that usual long term 
aging of precision crystals of a few 100 ppb or even one or two ppm may 
cause changes of TOT in the range of mK or less, which is
- much smaller than the accuracy of the determination of TOT
- neglictable compared to the impact of the aging of thermistors and of 
the frequency determining capacitors and inductors of the sustaining 
oscillator stage

Regards

Bernd
DK1AG