[time-nuts] Disciplining Rubidium
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.
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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