[time-nuts] oscillators

Rick Karlquist richard at karlquist.com
Thu Aug 30 17:14:14 UTC 2012

Hal Murray wrote:
> richard at karlquist.com said:
>> No it doesn't use a cheap crystal.  It uses a *special* SC cut crystal.
>> This
>> crystal could very easily cost more than an OCXO crystal.
> What's special about it?

First, it has to have no activity dips over the full
operating temperature range.  OCXO crystals only have to work
at the oven temperature.  Activity dips, according to John Vig,
are the reason whey they don't use mode B to sense temperature.

Second, it has to be cut correctly so that the beat note between
the fundamental times 3 and 3rd overtone modes is a useful
indicator of temperature.

> I assume the cost-more aspect would be to allow an overall goodness factor
> competitive with an OCXO in the low power corner of the marketplace.  It
> might be cheaper overall to use a good crystal and a uP to correct for
> temperature than provide the power to run the oven.

Again, the MCXO is not a poor man's OCXO.  It tends to be used
in applications such as manpack radios where battery constraints
rule out ovens, regardless of cost.

> --------
> The other area where a uP is useful is in an environment with high
> vibration.  It can correct for acceleration as well as temperature.  There

I've never heard of this being done.  Do you have a reference?

Rick Karlquist N6RK

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