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

Daniel Davson ddavson at peralex.com
Tue Jun 29 13:11:19 UTC 2010

Thanks for the response Björn. Also thanks to Didier Juges for pointing 
out that this has been covered on a previous thread. I'll go and find it 
in the history.

Unfortunately the device will be used in urban areas so some multipath & 
obstruction of skyview is expected. I've just done some testing on my 
OCXO and it has a maximum sensitivity of about 5 ppb / *g*, which is 
notable, but shouldn't present a problem. I've yet to explore the 
vibration effects - thanks for pointing my attention to the motion 
effects on the OCXO itself, its an aspect I'd otherwise have overlooked.


bg at lysator.liu.se wrote:
> Hi Daniel,
>> 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.
> Are you moving around in areas with little obstruction for the GPS antenna
> towards the sky? Then I would first look at the dynamics inpact on your
>> 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?
> Tilting/accelerating your GPS oscillator might possibly yield an effect.
> Other than that there is no theoretical advantage keeping your receiver
> stationary. All its measurements are done against satellites moving at ca
> 4km/s.

Daniel Davson
HW Design Engineer
Peralex Electronics (pty) ltd.
Peralex House, 5 Dreyersdal Rd, 
Bergvliet 7945, South Africa
Tel: +27 21 710 7446

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