[time-nuts] CSAC State of Play

[Lux, Jim]

On 1/12/21 2:04 AM, Nigel gm8pzr via time-nuts wrote:
> Thanks for the update, I'm getting a better picture now of what happened and it doesn't sound quite as bad
>
> as I'd thought, certainly makes them worth playing with anyway:-)

Very much so. They're a cool little device. The user manual describes 
the heater current limits. You need a serial port to talk to it and the 
primary output is the 1pps.  The 10MHz output isn't the best (except on 
the Low Phase Noise model), but it works.




>
>
>
> Nigel GM8PZR
>
>
> On 1/11/21 5:36 PM, Nigel gm8pzr via time-nuts wrote:
>> A few years ago SA45s CSAC modules were all the rage, and I was more than happy to acquire a few
>> as fallout from a UK MOD project.
>>
>> It wasn't too long after though that reports were suggesting earlier failures than expected, but I can't for the life of me remember why.
>> Something underwater does come to mind, a long term project that wasn't perhaps as long term as expected, either way someting went pear shaped, anyone have any idea of what it was and the current state of play?
> When manufacturing moved from the original Symmetricom plant, they sort
> of "lost the recipe", and they had an outgassing problem internally.
> There is a getter in there to hold the vacuum, but eventually it "fills
> up".  I don't recall if it was a seal that leaked, or some material that
> was gassy. The problem has been solved.
>
> The hotter you run them, the faster the getter fills up. So there are a
> bunch of these that have greatly restricted temperature ranges even for
> storage/non-operating(35C max.. I remember asking them whether they ship
> them with ice packs, because the back of the UPS truck in California in
> Summer is way higher than 40C)
>
> You can check the heater current to see if it's too gassy - as the
> vacuum goes away, it takes more heat to keep the physics package at the
> right temperature.
>
>
> Said Jackson did some analysis on CSACs that would not be on 24/7, and
> came up with a fairly decent lifetime.
>
> The story is that they were used in an underwater application (where
> temperature isn't an issue), but, in fact, they also sat on the deck of
> the ship in the sun, and had early failures (or faster than expected
> rise in heater current).
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