Re: oscillator design with a long xtal lead

Phil Hobbs wrote:
Rene Tschaggelar wrote:

Phil Hobbs wrote:

Rene Tschaggelar wrote:

Apparently yes. What is wrong with having the
oscillator in tha vacuum too ?


Normally the problem is outgassing. With attention to the cooling, you can make the oscillator work in the vacuum--but often you can't make the vacuum work with the oscillator.

This sort of oscillator is used in quartz film thickness gauges, for example. Tweaking the cable length is a good idea, but a half wavelength will work better than a quarter--it will reproduce the crystal impedance, whereas a quarter wave produces Z0**2/ZL. A quarter wave will make the crystal look inductive except between its series and parallel resonances, which will cause the oscillator to not work.

A coil, a cap and a SOT23 together with the XTAL
should be sufficient. No ? It the SOT23 producing
gasses ?


High and ultrahigh vacuum is a world to itself, and the rules are really different. I don't know what sort of vacuum the OP is contemplating, but if it's below 10**-6 torr, the cable idea is the right one. You can get low-outgassing cable, usually polyimide-insulated, with no jacket. Cables like that (and water-cooled holders for quartz oscillator crystals) are common throwaway vacuum system parts.

The circuit board is going to be the big killer. Also lots of vacuum systems need to be baked out at > 200C for hours and hours, which would get flux and various FR-4 exhalations all over *everything*. You could probably do this, e.g. on a sintered alumina substrate, but it wouldn't be a slam dunk, and you'd have to make it cleanable--really cleanable.


It'd skip the pcb and mount the components in 3D flying
anyway. Extended 200 degrees for outgassing is not really
according to the temperature profiles. The only part that
can realistically produce vapors is the SOT23, not the
coils, nor the ceramic cap.

Rene
.

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