[time-nuts] GPS orthodontics: sawteeth & hanging bridgestheeffect of time averaging

Tom Van Baak tvb at leapsecond.com
Sat Dec 23 03:44:25 UTC 2006


[ sorry for the earlier truncated posting ]

> Suppose that I'm now using the SR620 to make averages of 5,000 seconds
> and plotting those where the inputs are from an M12+T and a FTS4060
> Cesium standard.  At 5,000 seconds Ulrich's plot shows about 4E-12.
> Does that mean with a perfect standard I would expect to see noise of
> about 4E-12?

Or even a little better; perhaps under 1E-13.

> So I should set the averaging to about 1E6 seconds (11 days)? to get the
> best possible result?

Brooke,

You may continue using 5000 second averages. When
you use various ADEV programs, they will be able to
compute and plot at 5000 seconds and any multiples
of 5000 s, including out to 1e6, and beyond.

It's usually much better to collect many phase points
at smaller tau, rather than wait for (and risk) for a few
points at huge tau.

By running longer you will see where your FTS 4060
hits its noise floor. It may occur well before 11 days,
but you won't know until you take a month or two of
data.

A plain M12 is fine for this; you don't need a GPSDO.
Here's a 12-day run that you'll like:

http://www.leapsecond.com/pages/58503-cns2/

/tvb







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