[time-nuts] OCXO sensitive to gravity

John Miles jmiles at pop.net
Wed Sep 2 22:50:14 UTC 2009

> Someone commented a while back on the effect of gravity to a osc
> as it rotated thru its 3D axis.
> Attached, I've plotted the gravitational effects on the Freq of a
> HP10811 osc
> that has been placed in a box and tilted so that it is at its
> null turnover G axis.
> Plotted is the change in freq caused by sitting the box on each
> of its 6 sides for about 30 seconds
> and then rotating the box by hand (some what jittery) 360 deg in
> two different axis.
> The test was done mostly to test my Freq offset tester, but I
> found the results interesting enough to post.
> Max 2 G effect is 1.42 e-9.   All numbers are calibrated raw
> data, taken at
> 1e-12 resolution with a 0.5 sec filter, updated at 50 samples per
> minute.
> The samples between 28,300 28,450 where referenced to a GPS locked Tbolt,
> the rest of the plot was referenced to a second 10811 which has
> about 1/10 of the
> Tbolt's short term PP noise, visible only in the expanded graph at zero.

That's about what I saw when I turned my 5061A over on the workbench
(attached).  The large spikes are 90-degree turns starting from the normal
upright position, first to one side and then to the upside-down position,
allowing 2-3 minutes or the loop to recover each time.  The third spike is a
quick turnover back to upright.  The 10811-60109 oscillator is mounted with
its top surface facing the front panel.

-- john, KE5FX
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