On 12/30/12 8:03 PM, Bob Camp wrote:
Hi
They are using some pretty major fields in that paper. As they point out, high
level tests likely do not extrapolate well to low level performance. Their data
shows the impact diminishing quickly as the field drops.
If you accept their 1x10^-11 per gauss number as correct, your OCXO might see a
5x10^-12 change as you rotated it 90 degrees. Unless you have a very good OCXO,
that's not a big impact.
In the case of a fan that's likely generating mili gauss of field (you don't
get that much off of 50 ma at 12v), you could see 1x10^-13 level changes. Your
OCXO's AVAR is likely well above that at any tau that the fan messing with.
Yes, I'm making the assumption that the fan motor is not in contact with the
OCXO case. In any rational setup there will be at least a few inches between
the fan and the OCXO. Not exactly far field at 20 Hz, but the field does drop
off pretty fast.
A bigger concern might be if you're locking something you care about to
that oscillator. The PLL might be more sensitive (particularly things
like the op amp circuitry driving the VCO... there's probably some sort
of physical loop in the wiring between the inverting and noninverting
inputs of the op amp.
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