[time-nuts] Big Picture View
Keith E. Brandt, M.D.
wd9get at amsat.org
Wed Dec 12 15:45:13 EST 2007
That's a good start towards answering my question. Given my set-up of
GPS referenced NTP server, how would I integrate a frequency
reference into the system?
> As a relative newbie to the who time-nut scene, I'm still working on
> > the big picture of how all the hardware fits together. I've
> > successfully put together a FreeBSD box with a Garmin 18 LVC as an NTP
> > server and am getting consistent microsecond accuracy. I've been
> > looking at the next step of adding a stable oscillator to the system.
> > I'm not seeing how to integrate this into the system.
> > The way I understand it, the oscillator is there to provide a very
> > stable frequency reference, regardless of the type used --> VXCO,
> > rubidium, cesium, etc. What I'm not seeing is how you link the
> > frequency reference to UTC. For NTP, I'm guessing that you'd have to
> > sync a PPS pulse with a known time source such as GPS. Am I on the
> > right track? Pointers to references appreciated.
> > 73, Keith
>Hi Keith --
>Frequency isn't linked to UTC; phase is. What you're doing with an
>external oscillator is simply providing the computer with a stable clock
>frequency. The PPS signal from the GPS provides the phase information
>that tells NTP when the second marker is. The stable clock frequency
>just makes it easier for NTP to hold the second marker at the proper point.
>Even if the reference frequency is inaccurate (and that may be the
>question your asking), NTP is still better off as it can correct for a
>frequency offset more easily than it can a clock that is erratic.
>Hope this helps.
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