[time-nuts] Question on crystal jumps

Steve Rooke sar10538 at gmail.com
Thu Oct 23 10:35:37 UTC 2008

2008/10/23 Ron Smith <ronald.p.smith at btinternet.com>:
> The text says the curve of frequency against plate thickness does not give a
> straight line, but has discontinuities in it. These discontinuities they
> call "stepping points" and are a result of edge vibrations coinciding with
> sub-multiple frequencies of the wanted thickness vibration mode. The degree
> of coupling between the wanted and unwanted modes varies with crystal
> dimension. If there is zero coupling, the stepping points should not affect
> the main oscillation. But perhaps even the smallest change in dimension can
> cause it to cross one of these discontinuities and jump to and fro? I
> suspect that crystal sensitivity to stepping or jumping may be correlated
> with its temperature coefficient, although there are other factors
> (including gravitational) that influence frequency of oscillation at very
> small levels.

I have a counter that seems to exhibit a jump in it's timebase. From a
cold state a fixed frequency connected to the input shows a gradual
change as the unit heats up over an hour or two. Once it reaches a
stable state it will stay in that state for a couple of days and then
it will jump to a new stable state, and stay in that state however
long the unit is switched on. This is repeatable each time I switch
on. I have not observed the jump and there is no data output on the
counter to be able to record the times that this happens. All I know
is that there is a definite little jump after a long period of

73 - Steve
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet

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