[time-nuts] OCXO sensitive to gravity

WarrenS warrensjmail-one at yahoo.com
Wed Sep 2 21:01:32 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.

>When possible, the thing I do to eliminate the effect of small gravitational changes or tilt 
>from effecting the Freq of my Oscillators, is to orientate their case so that the osc is 
> approximately at its MAXIMUM 2G turn over axes. 
>This gives the osc a null to small gravitational changes, 
> much the same as setting the temp of an oven to the zero TC freq turn over point.
>To optimize further, the axes can be fine adjusted so that a small tilt in any direction 
> causes the same direction in freq shift.
>The improvement achieved can be quick substantial like 100 to 1 improvement. 
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