[ntp:questions] NTP absolute accuracy?
David Lord
snews at lordynet.org
Mon Nov 2 10:23:48 UTC 2009
Unruh wrote:
> "David J Taylor" <david-taylor at blueyonder.not-this-bit.nor-this.co.uk.invalid> writes:
>
>> "Unruh" <> wrote in message news:IEbHm.50125$Db2.41863 at edtnps83...
>> []
>>> MSF?
>
>> See:
>> http://www.npl.co.uk/science-technology/time-frequency/time/products-and-services/msf-radio-time-signal
>
>> UK 60KHz radio time signal.
>
> Ah, OK. Its accuracy is probably not much better than a few msec I assume.
> GPS is a few usec. Since the network gives accuracies of better than a few ms, MSF
> is not a good way of testing the accuracy of network set clocks.
>
Hi
I expected to get away with it from trying upstairs:
hrs % offset jitter % offset jitter % offset jitter
(ms) (ms) (ms) (ms) (ms) (ms)
100 50 0.185 0.086 95 0.642 0.255 99.5 1.111 0.488 frame aerial
70 50 0.362 0.172 95 0.802 0.370 99.5 1.057 0.495 ferrite-rod
With PPS driver added
hrs % offset jitter % offset jitter % offset jitter
(ms) (ms) (ms) (ms) (ms) (ms)
26 50 0.165 0.070 95 0.621 0.246 99.5 0.673 0.333 frame aerial
The % refers to logging at 30min intervals so 50% of offsets were
at or under 165us.
Having moved the receiver with ferrite-rod downstairs it's not so
good, I'm not yet setup for PPS driver.
hrs % offset jitter % offset jitter % offset jitter
(ms) (ms) (ms) (ms) (ms) (ms)
26 50 0.561 1.095 1.344
For same system using ntpd and internet from before using MSF:
hrs % offset jitter % offset jitter % offset jitter
(ms) (ms) (ms) (ms) (ms) (ms)
96 50 1.535 0.467 95 4.404 1.672 99.5 4.850 4.889
the other two servers from internet are better.
96 50 0.642 0.610 95 3.726 2.258 99.5 4.959 2.916
96 50 0.507 0.520 95 1.329 0.811 99.5 2.588 2.030
I'll try swapping to frame aerial and PPS module tonight but
I think I'm in a leaky faraday cage with wire mesh under the
plaster on the walls so for anything better will have to wait
until I've finished the units that will be mounted on mast
at rear of house.
David
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