[time-nuts] Setting Rubidium to match GPS source

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Sep 28 19:01:45 EDT 2007

SAIDJACK at aol.com wrote:
> Hi HMurray,
> depends on the GPSDO. On the Fury for example you can expect the unit to  
> wander less than +-15ns back and forth over a period of 1 Day. That's a  
> deviation of about 3.5E-013 or so per 24 hours.
> This wander depends on how good the hold position is that is set inside the  
> GPSDO's GPS receiver, as well as the stability of the OCXO, and the quality of 
>  the GPS receiver.
> All standard GPS receivers have problems with height:
> We see a range of about +-2 Meters max on the height on the Motorola M12+  
> receiver on different Fury units for example. The newer M12M motorola/iLotus  
> receiver is slightly better than this.
> This would lead to a worst case error of up to 12ns just due to this  antenna 
> position error, slightly more than a good Cesium would wander.
> Said

Where does the 12ns figure come from?

Surely a height error of 2m leads to a timing error of about 6.6ns for a
particular SV when that SV is directly overhead.
When the SV isnt directly overhead a 2m error in height contributes less
error than this to the slant range and the corresponding propagation
delay error from the SV to the antenna will be less than 6.6ns.


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