[ntp:questions] NTP absolute accuracy?
Terje.Mathisen at tmsw.no
Mon Nov 2 07:23:42 UTC 2009
> John Hasler<jhasler at newsguy.com> writes:
>> There isn't any tone. It's the UK equivalent of WWVB.
> How is the beginning of the second ( an hour) marked?
> The bandwidth of whatever marks it has to be pretty narrow, or the transmitter
> would interfer with everything around it. Ie, that means a large time uncertainty.
Not if they do the same spread spectrum modulation of the carrier as
emplyed by the German DCF77 transmitter: By phase-locking a receiver to
that signal, you can get down to the 10-30 us or so range.
(You still have to be close enough to the transmitter so that the
propagation path is perfectly predictable, otherwise you'll see
systematic excursions as a function of the time of day/night.)
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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