[CentOS] System Time Source

[Lamar Owen]

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 at 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.