On 05/24/2017 11:29 AM, Pete Biggs wrote:
...
The terrestrial radio clocks are actually not that accurate. They are
not designed for keeping things like a system clock "correct".
Commercial solutions only keep to within about +/- 0.5s per day, with
resynchronisation happening about once a day.
The GPS time system is also notoriously very precisely wrong. ...
Whee, I had to check headers to see if my input filters had started
pulling time-nuts@xxxxxxxx traffic into my CentOS folder..... and if you
want to discuss the ins and outs of serious timekeeping, you might find
that mailing list useful. (My $dayjob requires me to deal with that
kind of precision.)
No one has mentioned using the most ubiquitous of the time sync sources,
though, and that's the digital cellular network. Any one of GSM, 4GLTE,
or 3G or even old CDMA2000 works, and will have very precise time (it's
required for the protocols for the phones to be locked to the base
station's time, and most base stations use GPS or SONET timing signals
and either disciplined OCXO's or rubidium standards frequency-locked to
the GPS 1PPS or the SONET frame clock. Even a real T1 provided from the
telco is traceable to a cesium PRS somewhere. ).
One such standalone box is made by Beagle Software; see
http://www.beaglesoft.com/celsynhome.htm and while it's not exactly
cheap, the concept could be extended to use one of the commonly
available SDR dongles (like an RTL-SDR) and the timecode could be
retrieved with software. No cell account is required to receive the
timecode.
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