[time-nuts] Motion effects on accuracy of GPS pps

Daniel Davson ddavson at peralex.com
Tue Jun 29 04:13:28 EDT 2010


Hi,

I've recently completed a GPSDO using the pps output of a uBlox Antaris 
TIM4 GPS module to discipline a 10MHz OCXO. I'm now investigating the 
motion effects (acceleration/uniform velocity) on the accuracy of the 
time-pulse and hence on my frequency output.

I've been unable to find any detailed information on the relationship 
between the accuracy of the pps output and the effects of having the 
receiver in motion (i.e. in a car/boat, at velocities far below the 
modules operating limit of 515m/s) - I'd appreciate some input on this 
matter. Does motion cause increased jitter? Is it possible for it to 
cause a phase error in the pps output for a finite duration? I suspect 
that the averaging I am doing on my phase measurements will eliminate 
the effects (600 samples, 1 second apart), but if the error introduced 
is significant I'll most likely add monitoring of the DOP information 
and disable the GPSDO when the TDOP is too high.

The product's system integration manual does indicate that is possible 
to use an accuracy mask, which theoretically imposes a limit on the 
accuracy of the output, however this information is quite vague - 
emailing uBlox support has yet to yield a response.

Best Regards,
Daniel Davson

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