[time-nuts] Disciplining Rubidium
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.
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