[ntp:questions] Accuracy of GPS satellite signal ?

Eugen COCA ecoca at eed.usv.ro
Tue Jan 30 19:48:11 UTC 2007


Ron,

as I said in my response, there are many other factors with a great 
influence on the precision. The rubidium oscillator stabilizing the 
PPS signal has near zero effect if you do not change the motherboard 
crystal. The temperature has a great influence on the stability, I 
observed variations of more that 20 to 50 microseconds in the interval 
from 10 to 35 degrees.


On Jan 30, 10:55 am, "Rob Kimberley" <time.ban... at btinternet.com> 
wrote:
> Hi Richard
>
> 500nS is very achievable with GPS. In fact, once installed and running for
> 24 hours, you will see better than a factor of 10 than that.
>
> Factors to bear in mind though for this type of application....
>
> 1) Use exactly the same hardware at each site.
>
> 2) Antenna cable - important to ensure that you enter the correct antenna
> delay figure when setting up the receiver to allow for cable delays
> (remember you GPS position and hence your time is at the antenna and not the
> receiver). 1nS per foot is a good estimate, so a long cable run (with
> amplifiers etc) would quiclky put your system time off without the correct
> compensation figure.
>
> 3) Oscillator - a good quality OCXO or most likely a Rubidium are needed, to
> allow decent holdover in the unlikely event of loss of GPS. For your 500nS
> mission statement, my personal recommendation would be Rubidium, as an OCXO
> would quickly pass the 500nS figure if the unit had to flywheel.
>
> Good luck.
>
> Rob Kimberley
>
> "Richard Eich" <richard.e... at domain.invalid> wrote in message
>
> news:MPG.20242eda85df705498ad46 at news.verizon.net...
>
> > Paul.Cro... at softwareag.com wrote...
> >> Richard,
>
> >> Try clicking on this link:
> >>http://tf.nist.gov/timefreq/time/gps.htm
>
> >> You can achieve precision anywhere between a few milliseconds and a few
> >> nanoseconds,
> >> depending on how much you are willing to invest. Have you asked
> >> yourself how much
> >> precision the application needs? You can almost certainly achieve it!
>
> > Great link, thank you.
>
> > The app needs 500ns precision.  We can set up GPS at each locality,
> > but there was a concern about the relative accuracy of GPS receiver
> > timestamps if they're sync'ing to different physical sats.





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