[ntp:questions] Change reference clock soon after DCF-signalislost

Matuschka, Sebastian Sebastian.Matuschka at gcd-solutions.de
Thu Jul 15 09:25:17 UTC 2010

> I think this isn't a good design.
> In my experience, DCF-77 reception is simply not stable enough to
> directly
> use the pulses from the receiver as clock ticks.
> When there are thunderstorms, local interference, and sometimes
> propagation
> problems, there can be spurious extra pulses that you do not want to
> count.  Or pulses can be missing.
> A good way of using DCF-77 is to collect the 59 pulses that make up a
> minute, average the offset between the pulse start and the local clock
> tick,
> decode the time from the pulse lengths, and then at the end of the
> minute
> decide if all this information is valid and should control the clock
> (adjusting the clock offset/frequency), or should be discarded as a
> whole.
> This is also what the DCF-77 drivers in ntpd do.

Sorry, i forgot to mention an important thing:
The DCF-77 Signal is generated by a precise clock that is connected via
fiber optics to the device the ntpd runs at.
The distance isn't very long, so i can expect that the signal is very
precisely and there is no jitter nor any (relevant) offset.
So, it has not really has anything to do with a normal DCF-77 receiver.
I hope my questions make more sense now :)

Best Regards

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