[ntp:questions] Frequency Offset

Dave Hart hart at ntp.org
Fri Feb 24 05:53:48 UTC 2012

On Fri, Feb 24, 2012 at 02:20, Alby VA <albyva at empire.org> wrote:
>  Thanks. I needed that NTP 101 lesson. So is it a stretch to try and
> obtain a quality motherboard to improve the frequency offset?

The gross error of 25 PPM is on the good side.  It's not uncommon to
see several times that much.  But the gross error isn't the
interesting part -- ntpd will handle it pretty well.  The
temperature-induced variation at around 1PPM per degree C is the major
uncompensated error.  Finding the appropriate crystal and insulating
it to slow its temperature change as its environment changes is
probably the low-hanging fruit in improving your clock accuracy.  Next
steps are more invasive, such as moving the crystal out of the
interior to the presumably-less-variable temperatures outside the
case, replacing it with a TCXO or OCXO.

I recall Dr. Mills describing DEC Alpha machines has having
particularly good oscillators because designers were willing to spend
wee bit more than the minimum, but I don't remember what approach was
taken to improve on the common quartz crystal approach.

Dave Hart

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