[time-nuts] Caveats on Allan Deviation with ultra stable oscillators

Poul-Henning Kamp phk at phk.freebsd.dk
Fri May 30 18:24:03 EDT 2014


In message <013401cf7c46$31ac3cc0$9504b640$@miles.io>, "John Miles" writes:

>(Some
>people have even reported similar behavior with cesium standards, although I
>don't see how that could happen.  There aren't supposed to be any
>first-order temperature effects in a CBT, and I'd think that any lower-order
>effects would be way beneath the tube's flicker floor...)

One important trick in this area:

Always locate your DUTs physically orthogonal to each other.

Almost none of our DUTs have 3 axis of symmetry, and therefore
most environmental effects are not symmetric with respect to
orientation.

I noticed this by accident comparing three "identical" OCXO's
because I had put one of them in a different orientation than
the other two:  The environmental noise were much larger between
that one and the two other, than between the two co-aligned
DUTs.

I'm not entirely sure this is relevant for Rb/Cs/H, their environmentals
should be attenuated enough for it to not matter.


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
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