[time-nuts] Vibration isolation of quartz oscillators

[ed breya]

I have mounted OCXOs, Rbs, and PLOs on small rubber motor mounts - the 
kind like for fan vibration reduction and such. The problem is that it's 
more of a guessing/empirical task, with no idea of the actual 
susceptibility of the device, or the mounting attenuation specs or 
degree of improvement, without doing actual mechanical vibration tests.

If you have access to a commercial shake table or driver, you can 
readily make such tests. You can make crude DIY shaker setups with 
motors or big loudspeakers to rattle things around, and with proper 
instrumentation, measure the acceleration, displacement, frequency, etc. 
It can get quite complicated though. In any case, with DUTs like these, 
you also have to isolate the effects of magnetic emissions from the 
mover, from the true mechanical displacement effects, by adequate 
shielding and distance, and making comparative measurements. It's a lot 
of stuff to go through.

I think the simplest approach, and most effective in all axes, would be 
to mount the unit in a box of rubbery foam padding material. Of course, 
with an OCXO, you don't want it to insulate too well - the power has to 
be dissipated, and the foam has to handle the operating case 
temperature, so the thermal and material issues would need to be worked out.

If the available space is too small for at least a cm or so foam all 
around, you can look for small vibration isolation mounts, which should 
be available in all sorts of characteristics. Another possibility is to 
suspend the unit assembly on a thin rubber sheet, or from metal 
expansion springs or rubber o-rings tensioned in opposing directions as 
needed. For metal springs, you'd want to use lightest "k" ones as 
possible, that will adequately support the mass, with bits of foam 
shoved inside them to dampen self-resonances. Anyway, there are a lot of 
of options, but you still won't know how well they work without actual 
testing.

Ed