[ntp:questions] Accuracy of GPS satellite signal ?

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Wed Jan 24 20:32:33 UTC 2007


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?

How much money are you willing to spend?


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
interesting.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




More information about the questions mailing list