[time-nuts] Disciplining Rubidium

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Apr 24 20:50:35 EDT 2008

SAIDJACK at aol.com wrote:
> Hi guys,
> let me play the bad cop here:
>   1) Since it is easy and inexpensive to get OCXO's that have  stabilities of 
> parts to the E-012 or even E-013 (10811 on Ebay for $50 for  example) over 
> time periods of 1/10s out to hundreds or even thousands of  seconds
>   2) Since even the best Carrier Phase system won't give you much more  than 
> 1ns or so accuracy (from the previous threads) per second, and  maybe parts to 
> the E-013 over 100s or so - which is worse, or just as good as  our venerable 
> OCXO for short time frames.
Wildly inaccurate statement #2.
A carrier phase system gives can have noise as low as 20 picoseconds 
over the 1-100s time interval.
Upper time interval limit  may be a little larger.
>   3) Since the standard GPS stability seems to overlap our OCXO  stability 
> just about at the right point to achieve overall E-012 to E-013  performance at 
> about 500 - 2000s intervalls on typical GPSDO's
> Then why would we need a carrier phase driven GPSDO? What would  it give us 
> in performance that we cannot achieve today with say a good (surveyed  antenna) 
> M12M driving an excellent OCXO?
They can be almost 2 orders of magnitude better than you assume for 
short time intervals.
8E-14 performance from 2 to 20 s with 1E-14 at 1 day has been claimed 
when carrier phase disciplining  a BVA OCXO.
> The only advantage I could maybe see is that the carrier phase GPSDO would  
> bring us down to E-014 a bit faster than the M12M could?
Carrier phase disciplining should allow very good performance even with 
lower spec OCXOs.
> bye,
> Said

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