[time-nuts] Vibration isolation of quartz oscillators

[Bob kb8tq]

Hi

First thing to find out is what the per axis sensitivities of your oscillators
are. There should be significant variation between the three directions. 
What you find on one may or may not be what you find on the rest. 
Just about any source of (single directional) vibration will work for this test.
Measure the phase noise sidebands at the vibe frequency and go from
there. As long as the input is < 100 Hz you should be away. from any
internal resonances. 

Next step is to measure the vibe levels in your masers on an axis by axis
basis. This may take a while to do. You want to see what all the bumps and
thumps from operating this or that ( pump …) contribute. 

Conventional vibe isolators will help you above 100 Hz. If you have significant
energy up there, you may want to do a proper sweep of your OCXO’s on
a vibe table. There *will* be resonances ….

The rubber tubing (and other similar approaches) damping is aimed at getting
down into the 10’s or even single Hz range for significant attenuation. The 
trick is that you don’t want things very tight. Tight gets you more of a resonance.
You want damping. Hanging on a loose tube is better (attenuation wise) than
suspended between a set of tight tubes. 

Indeed having things hang loose inside the Maser is less than ideal if you ever
need to *move* the beast … there is a bit of a tradeoff. 

Wires and cables get into the act. Flexing a piece of coax can impart phase 
modulation. This is also worth watching out for when you test your OCXO’s. 
Taping the coax down is normally adequate when testing. 

Pretty much any good OCXO should have a worst case vector sensitivity
< 2 ppb / g. I would expect a good SC to be below 5x10^-10 / g. A good BVA
should be even better. 

What tubing works best? What lasts the longest? What do you have in stock?
I’d start with silicone based rubber tubing. It should last the longest. It’s also
fairly easy to get. 

Lots of fun !!

Bob

> On Jun 27, 2020, at 8:02 AM, Michael Wouters <michaeljwouters at gmail.com> wrote:
> 
> I have three Oscilloquartz 8607-Bs that I'm rehousing.
> 
> In their former life they were part of the frequency synthesis chains
> for H-masers and they hung vertically from a rubber suspension that was
> presumably intended to provide vibration isolation. Unfortunately, the
> person responsible for this has long since retired so is no longer
> around to ask questions of.
> 
> In the experiment I will be averaging over  100 s, which suggests to
> me that very low frequencies are what I need to filter out (if at
> all), and I am skeptical that the rubber will do this. Space is tight
> so I am wondering
> whether I should simply ditch the isolation.
> 
> What do other people do with their quartzes ? I thought I should ask
> for some advice before attempting measurements.
> 
> Cheers
> Michael
> 
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