[ntp:questions] how do I lock in average frequency correction

Dave Hart hart at ntp.org
Mon Feb 13 07:36:25 UTC 2012

On Sun, Feb 12, 2012 at 19:03, Chuck Swiger <cswiger at mac.com> wrote:
> On Feb 12, 2012, at 9:36 AM, unruh wrote:
>> The clock crystal ages, and suffers internal crystal "cracks"
>> migrations, etc, which change the frequency of the crystal. Thus even in
>> a temperature controlled oven, the crystal frequency will change, but
>> much of the crystal frequency change is driven by temperature changes.
> Agreed, temperature swings will have a major impact on the crystal frequency.

Well, I know what you're saying but we're talking on the order of 1
PPM / degree C.

> You might be able to improve the stability of the crystal by ensuring good
> airflow and cooling via HVAC as needed.  And I suppose you could adjust the
> rate by changing the HVAC set-point, but I don't think the benefit is worth it.
> I'd be more likely switch to an OXCO + GPS on a PCI/PCIe card if such as needed.

That's OCXO, oven controlled crystal oscillator.  Why X for crystal?
Christ if I know.  There's a great article at


that includes a table of abbreviations you can refer to.

Dave Hart

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