[time-nuts] generalization of three cornered hat

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Jun 16 11:22:05 UTC 2019


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>Note that when you consider transitive measurement noise, you may find 
>that making N simultaneous measurements against a single independent LO 
>is simpler and better than making N(N-1)/2 measurements of all possible 
>clock pairs. Think of star vs. ring vs. mesh networks.

I think there is a fundamental assumption that needs to be stated clearly here:

3-cornered hat and it's extensions are only productive with homogenous,
and preferably identical, sources.  Ie: 3 identical OCXO's, 3 HP5071As.

If you do a 3CH on a raw GPS-PPS, an Rb and a H-maser, you get a really
shitty result, because it attributes the worst properties of each source
to the "virtual source".

For heterogenous sources, pretty much all proposed time-scale
algorithms degenerate to 1st or 2nd order PLLs with suitably chosen
parameters and filters.

Arguably, the most important property of any timescale algorithm
is the ability to alert and exclude false-tickers as early as
possible, which makes Kalman filters obvious, despite their quirks.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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