[ntp:questions] Onboard Local Oscillator Change Improvements
John Ackermann N8UR
jra at febo.com
Wed Oct 10 18:59:30 UTC 2007
Jason Rabel said the following on 10/10/2007 02:47 PM:
> A better oscillator in the PC would really only mean better holdover when
> all NTP sources are unavailable. But even at that, depending on the OS and
> load, time could wander off just as quick even with the oscillator upgrade.
> Power regulation could be another factor, not just the AC power coming in,
> but the quality of the PC's PSU, or heck even the voltage regulators on the
> motherboard. You can pick apart literally a thousand different variables for
> a PC that are going to affect time keeping. But the complexities of the
> hardware itself and the OS are more your problem than the oscillator.
I don't think I entirely agree. A better oscillator in the PC should
also improve short term stability. When the $0.09 crystal wobbles due
to temperature or voltage changes, it takes NTP some time to adjust; the
loop time constants are quite long. If you look closely using an
external reference, these wobbles in timekeeping can be quite apparent
even on a PPS-sync'd PC. A better oscillator will wobble less and
consequently will improve short term stability.
That may or may not be relevant, depending on the design goals of the
And, come to think of it, a good oscillator may make more improvement in
a Stratum 2 machine because the control loop is likely to be much longer
than with a local refclock.
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