[time-nuts] Fundamental limits on performance
bruce.griffiths at xtra.co.nz
Thu Sep 17 04:08:14 UTC 2009
Bruce Griffiths wrote:
> Chris Caudle wrote:
>>> From: Mark Spencer <mspencer12345 at yahoo.ca>
>>> For anyone who is interested here is a bit more info about the USO's used
>>> in deep space applications and some comments abou the crystal based USO's
>> I found it interesting that one of the limits of stability seems to be the
>> ability to process the crystals at high temperatures to drive off
>> impurities. The JHU crystals are apparently in some type of glass
>> enclosure which can take the high temperatures, and the paper seemed to
>> indicate that the standard metal capped packages can't take the higher
> Bliley BFG61 package:
That should be BG61 not BFG61.
>> I had forgotten until I read that paper that Fox has crystals which are
>> packaged in quartz packages. I couldn't find any information on how the
>> packages are assembled, so I don't know if the assembly process could
>> handle the higher temperatures, but obviously if the package really is
>> pure quartz, it should be able to handle temperatures as high as the
>> quartz resonator.
> The upper temperature limit is when the crystalline quartz undergoes an
> irreversible phase transition to a non piezoelectric form.
>> I would assume that the package is in two parts, and
>> has contacts that penetrate the lower part of the package to connect the
>> resonator to the surface mount pads on the bottom surface of the package,
>> so it might depend on how the penetration is sealed, and how the top and
>> bottom parts of the package are attached together.
>> Just seemed interesting, I would assume that the JHU guys know about those
>> types of advances in packaging, but the paper didn't mention it.
> Look at the JHU site there is a little on the oscillator.
> The BFG61 package uses an intermediate internal ceramic plate that more
> closely matches the thermal expansion of the quartz crystal.
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