[time-nuts] Project GREAT - Galloping Galileo version

[Bob kb8tq]

Hi

Once you get up to an OCXO sized package, you get quite a bit of volume. 
On an older TCXO design it’s sort of the same thing. The CSAC falls into
a size range that is kind of on the borderline. I have seen packages that
size vented in the past.

Bob

> On Dec 9, 2018, at 10:39 AM, jimlux <jimlux at earthlink.net> wrote:
> 
> On 12/9/18 7:08 AM, Bob kb8tq wrote:
>> Hi
>> On a normal OCXO or TCXO design you would put the product in a
>> package with a hermetic outer wall to keep out crud and moisture.
>> Per the papers cited you would put a small vent hole in a “space grade”
>> product. Every time I see an eBay listing with a nutty price on a “space
>> OCXO” I wonder if it’s been sitting “vented” on a nice humid / dusty shelf for
>> decades.
> 
> Actually, you could have hermetic packaging - as long as you show that the pressure differential won't cause a problem.   Tons of ceramic ICs have hermetic packages (an a variety of XOs, as well).
> 
> It's sort of a judgement/analysis call - if it's something which is a box with boards, probably easier to vent - if it's something tiny, and people have been making and flying them for decades, then hermetic.
> 
> We do lots of thick and thin film hybrid circuits which are hermetic - e-beam welding of the lids and all.
> 
> 
> 
> 
> 
>> Indeed the only way to test / use  product vented like that is to put it in a
>> thermal / vacuum chamber (or fly it to outer space). While my basement
>> has a reasonable selection of this and that, I don’t seem to have missed
>> out on picking up a thermal vac chamber ….
>> How different is the performance with air in the package? It turns out to
>> be very much a “that depends” sort of thing. Usually not as big a deal
>> on a TCXO as on an OCXO.
> 
> for the CSAC, apparently, gas outside the physics package affects the heat required to keep the gas vaporized in the optical cell.
> 
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