[time-nuts] Vibration isolation of quartz oscillators

[Tom Van Baak]

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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