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@febo.com 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.