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

Magnus Danielson magnus at rubidium.dyndns.org
Tue Jun 29 17:39:50 EDT 2010


On 06/29/2010 10:32 AM, 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
> OCXO.
>
>>
>> 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.
>

I disagree... for some receivers...

As you line up you pseudo-ranges you now have to solve only the T 
variable rather than the XYZT position. This means that all 
pseudo-ranges is available for solving the T solution and reducing the 
TDOP error. The T-RAIM is also able to drop more false-tickers.

For receivers not having a T mode only but normal 3D or 2D mode, the 
benefit of fixed location is of less concern.

So, for a receiver at a fixed location knowing it has a fixed location 
it may be a benefit.

Cheers,
Magnus




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