[time-nuts] Practical considerations making a lab standard with an LTE lite

Magnus Danielson magnus at rubidium.dyndns.org
Sun Nov 23 09:03:10 EST 2014

NIST did something similar for their WWWV site, where they used bottled 
water in its staple packaging to build a thermal mass. They measured how 
their atomic clocks and rig behaved before and after, and could see the 
difference. Very neat way of using off the (store)shelf components for a 

Another aspect is to think about what kind of heating/coolling you have. 
If it can act more as a proportional system rather than bang-bang 
regulations, it won't produce as drastic swings for you.


On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
> --------
> In message <20141123153744.bioKftA5 at smtp16.mail.yandex.net>, Charles Steinmetz
> writes:
>> First, mount the LTE in a cast aluminum box (not thin sheet metal,
>> something with some heft). [...]
> Charles' design has some good points, but I don't agree with it.
> What you are trying to do is to low-pass filter any thermal signals
> before they reach the LTE or OCXO.
> Charles' design works great from the outside, but doesn't do anything
> with respect to the thermal energy expended by the encapsulated
> device themselves, which will cause convection in the inner box.
> (For LTE and OCXO it is probably less of a problem that changing
> power-disipation will have a outsized effect on the central
> temperature.)
> Here is a much simpler and likely cheaper way to do it:
> Put the LTE or OCXO in a small box of your choice.  Even a cardboard
> box is fine.  A little thermal insulation in the box is OK, but not
> too much, the heat must be able to get out.
> Find a medium sized cardboard box, something like a cubic feet or so.
> Place it where you want your house-standard, with some kind of
> thermal insulation under it, two layers of old rug will do fine.
> Lay a floor of bricks inside the box.
> Build a "wall" of bricks along the outside of the box.
> Place the smaller box in the hole in the middle, cut the
> corner of a brick to run the cables without too much leakage.
> Use a floortile as roof, possibly with a layer of bricks on top.
> Close the outher cardboard box with tape to minimize convection.
> Congratulations, you now have a cheap and incredibly efficient
> thermal low-pas filter, which will allow thermal energy to move in
> both directions -- eventually.
> The outher cardboard box is not optional, unless you replace it
> with some other "mostly air-tight" barrier.
> The little bit of insulation the outher cardboard adds are not a
> bad idea either, for instance it reduces the effect of sunlight
> hits the box at certain times of the day/year.
> But you can substitute any geological building material you have
> at hand for the bricks, because the trick is that geological building
> materials have just the right thermal properties we are looking
> for:  Decent but not too good thermal conductivity with healthy
> dose of thermal mass.
> Cinderblocks comes with convenient interior holes premade.
> Aerated concrete blocks are also a candidate material but
> don't make it too thick since it insulates quite well, and
> paint the surface to bind the dust.

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