[ntp:questions] Accuracy of GPS satellite signal ?
richard.eich at domain.invalid
Fri Jan 26 20:33:07 UTC 2007
hal-usenet at ip-64-139-1-69.sjc.megapath.net wrote...
> In article <MPG.202131877f6d3e0498ad41 at news.verizon.net>,
> Richard Eich <richard.eich at domain.invalid> writes:
> >If I were to set up five or six global locations, each time-
> >synchronized to a local GPS receiver, how much variability would I
> >expect there to be between the time as indicated by the GPS
> >satellites used by each local GPS receiver.
> What decimal point are you interested in?
> nanaseconds? microseconds? milliseconds?
> Are you interested in the time out of the GPS box
> or the time out of an NTP server connected to a GPS box?
The time out of the GPS receiver. The GPS receiver will be
physically attached to the device to be sync'ed; no NTP.
> How much money are you willing to spend?
It always gets down to that, doesn't it?
> The GPS side depends upon how fancy your gear is and how
> good your antenna location is. The speed of light is
> a foot per nanosecond. GPS position accuracy for consumer
> gear is generally within a few 10s of feet so time accuracy
> should be within a few 10s of nanoseconds. The national
> standards laboratories use GPS to compare their atomic
> clocks so you can get very very good if you work hard enough.
> With a bit of work, you can probably get a NTP server using
> GPS to be within a few/10s of microseconds. That's good enough
> so that you can easily measure asymmetries or jumps in network
> routing. (assuming similar setups on both ends)
> Getting the time from a good NTP server to other systems gets
Thanks very much for your help.
More information about the questions