[time-nuts] Project GREAT - Galloping Galileo version

[jimlux]

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.