[ntp:questions] Question on loopstats and PPS

Pedro Torres torres at pop-pr.rnp.br
Wed Dec 14 16:58:14 UTC 2005


Hi Mauro,

Em Qua 14 Dez 2005 12:27, Mauro Fiacco escreveu:
> Hi to All,
>
> I am tryng to evaluate how good is my NTP server. It runs freeBSD and
> uses a rubidium PPS signal to discipline the frequency (no time
> correction).
>
> The following loopstats is typical:
>
> 53667 64119.201 0.000000000 32.241623 0.000000954 0.003332 6
> 53667 64184.203 0.000000000 32.233749 0.000000954 0.004881 6
> 53667 64248.196 0.000000000 32.233749 0.000000954 0.004227 6
> 53667 64311.199 0.000000000 32.233749 0.000000954 0.003661 6
> 53667 64377.202 0.000000000 32.233749 0.000000954 0.003170 6
> 53667 64443.205 0.000000000 32.223343 0.000000954 0.005883 6
>
> The Time offset is 0, as it does not know any better; the stability is
> reasonable... But why the frequency offset (4th field) is so high?
>
> The status reported by ntptime, shows that the FLL and PPSSIGNAL are
> active.
>
> Shouldn't the frequency be corrected within the capability of the PPS
> signal?
>
> I understand that this value may be the frequency offset measured by
> PPS.
>
> In this case my question is: how can I calculate the Allan deviation of
> my server without knowing the actual frequency offset?

I think 6th field is Allan deviation.

Pedro



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