[time-nuts] Disciplining Rubidium

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Apr 23 20:58:18 EDT 2008

SAIDJACK at aol.com wrote:
> One more comment:
> the GPS disciplining doesn't affect performance of parts to the 14th  short 
> term. GPS is used for long-term (>1000s or so) error correction, where  it can 
> achieve parts the 14th, but only after a day or much longer.
> GPS is not good enough to give you more than parts to the 8th-9th timing  
> accuracy per second, which is already accuracy in the feet range. Parts to  the 
> 14th short term would require accuracy in the 0.00001 foot range, not  possible.
> bye,
> Said

Only true if you dont use carrier phase measurements to discipline the OCXO.
When carrier phase discipling is used then a short term (1 - 100sec) 
phase error measurement noise of around 2E-11/Tau is possible.
However the accuracy at 1 day is limited to around 1E-14 by the SV local 
oscillator instability and other phase delay instabilities.


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