[time-nuts] Vibration isolation of quartz oscillators

[George Dubovsky]

Through the mysteries of business consolidation and the resulting asset
transfers, I have in my Virginia basement a rather nice Zeiss metallurgical
microscope (which I have absolutely no use for but I couldn't stand to see
consigned to a dumpster), which is perched on its original mount, a
30"x48"x4" granite slab. The slab sits on a square-tube-steel table that is
actually a low-pressure vessel that has four round rubber bladders mounted
in the top corners, holding up the slab. Each bladder has its own valve
which has a short arm that contacts the bottom of the slab and servos that
corner of the slab. This marvellous air-suspension microscope has tags
indicating it came from AT&T Bell Labs in NJ. Since it shares the basement
with three milling machines and one lathe, my kids will already have their
hands full when my time comes, so what the hell... ;-)

73,

geo - n4ua

On Sun, Jun 28, 2020 at 7:44 AM Tom Van Baak <tvb at leapsecond.com> wrote:

> About slabs and stability... Around the world there must be a hundred
> precision time labs, including official NMI (National Metrology
> Institute) labs that contribute to the calculation of UTC itself. You
> run into photos of these labs and their T&F gear on the web all the time
> when you search for time nutty stuff. Those of us with home labs -- even
> if just a few vintage frequency standards -- can relate.
>
> Anyone, one of my favorite lab photos is from VSL, the Dutch Metrology
> Institute. Photo attached. [1]
>
> Spend time time pan/zooming around the gear in the photo. The usual
> suspects: hp 105 quartz; TimeTech (I think); lots of SDI
> (Spectradynamics); also Truetime or Symmetricom stuff; maybe that's an
> old Tracor/Fluke VLF receiver on the far right (?); and of course lots
> of Stanford Research SR620 counters, the TIC still used by almost every
> time lab.
>
> But what really caught my eye was not just the four hp 5071A in the
> foreground but *how they are mounted* -- on top of massive granite blocks!
>
> The answer is [42]. In this case the question is how many cm wide is a
> 5071A cesium clock? That means the scale of the 1600x1200 JPG is about
> 1.5 mm per pixel, which implies the blocks are exactly 50x50x40 cm.
> That's nearly half a ton of mass. Note the unknown mystery support
> technique underneath. Either they had spare black granite blocks lying
> around their office that looked really cool or they put some thought
> into vibration isolation of their clocks. Still, tell me more about
> inner tubes.
>
> I personally don't know the background of this setup. If you have VSL or
> .NL connections please let us know. I remember when I first talked with
> them about their lab many years ago, the UTC(VSL) BIPM stability numbers
> seemed unusually good to me for "a national lab with only 4 cesium
> clocks" so the granite blocks left a heavy impression on me.
>
> Anyway, for those of you looking for maximum quartz oscillator /
> frequency standard stability and vibration isolation, maybe the granite
> block isolation idea is worth looking into. I know Michael mentioned
> space constraints for his BVA so this rock solid slab solution might not
> help him.
>
> /tvb
>
> [1] I can't find the original vsl.nl web photo that I remember. But a
> recent one like it is:
>
> https://elpromatime.com/wp-content/uploads/2018/10/VSL.jpg , via:
>
> https://elpromatime.com/portfolio_page/time-server-nts9000 , via:
>
> many google image searches for words including: VSL dutch metrology .nl
> caesium 5071a clocks UTC BIPM
>
> [42]
>
> https://en.wikipedia.org/wiki/42_(number)#The_Hitchhiker's_Guide_to_the_Galaxy
>
>
> On 6/27/2020 5:09 PM, Neville Michie wrote:
> > An old trick I learned from an Australian standards lab was to make a
> vibration free
> > table with a 2 foot by 2 foot by 2 inch paving slab supported by a
> partly inflated
> > wheel barrow inner tube.
> > I tried it recently for measurements of force in an electric clock
> movement
> > and it cut out the background vibration in a spectacular way.
> > cheers, Neville Michie
> >
> >> On 27 Jun 2020, at 22:02, 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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