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

Chuck Swiger cswiger at mac.com
Mon Feb 13 18:59:08 UTC 2012


On Feb 12, 2012, at 11:36 PM, Dave Hart wrote:
>> 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.

Yeah, on that order.  It's noticeable, or can be anyway, but also well within
the tolerances that ntpd will handle just fine.

>> 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
> 
> http://en.wikipedia.org/wiki/Crystal_oscillator
> 
> that includes a table of abbreviations you can refer to.

Yes, "OCXO".  Electronic schematic diagrams use single or two letter abbreviations, and
"C" was already taken (for "Capacitor").  I seem to recall a crystal is actually "Y" if
using a single letter, or "XO" for two letters....

Regards,
-- 
-Chuck



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