[ntp:questions] Accuracy of GPS satellite signal ?

Rob Kimberley time.bandit at btinternet.com
Tue Jan 30 08:55:36 UTC 2007

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.eich at domain.invalid> wrote in message 
news:MPG.20242eda85df705498ad46 at news.verizon.net...
> Paul.Croome 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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