[time-nuts] Practical considerations making a lab standard with an LTE lite
wb4gcs at wb4gcs.org
Sun Nov 23 09:30:57 EST 2014
I am enjoying this thread. These are all very interesting ideas.
Hoping to power up my first unit later today....
I'm putting my LTE-Lite in the recommended HAMMOND box. That takes care
of the box with air. I was then considering proportional heating of the
surface of the box, like I did long ago with some GUNNPLEXERS -- seemed
to work pretty well. Then this whole assembly goes inside two or four
inches of the foam insulation.
Now, the question becomes, to what temperature to heat it? With a
crystal, I'd plot /f/ vs. /T/, and look for minimum slope. How to do
that with LTE-Lite -- plot /efc/ vs /T/ and look for either center of
range or minimum slope??
wb4gcs at amsat.org
On 11/23/2014 9:03 AM, Magnus Danielson wrote:
> 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 test.
> 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
>>> 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
>> 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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