oscillator design with a long xtal lead

[Rich Grise]

Hello Tim,


If they can get whole IR iamging sensors in there it shouldn't be a big
deal to get a wee oscillator in there. It could be encapsulated in
glass. I have some very low frequency crystals that are housed in glass
and there is at least 1/4 of a cubic inch of space in there.

The simplest oscillator to run with a crystal would be a tiny unbuffered
logic single-inverter and a resistor. Pretty much the size of a few
grains of salt.

How about a TOOB? Heck, in a UHV chamber, you could run it naked! ;-D

Cheers!
Rich

 

[Joerg]

Hello Rich,

How about a TOOB? Heck, in a UHV chamber, you could run it naked! ;-D

I was actually thinking about one, a little nuvistor tube. But I didn't
post to avoid being pelted.

Regards, Joerg

 

[Rene Tschaggelar]

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

 

[Rene Tschaggelar]

Hello Phil,


Ok then, here is another idea: Create a low end impedance analyzer on
the outside and instead of oscillating monitor the crystal parameters.
With clever software it should be possible to compensate for the cable
characteristics and their changes with temperature.

Joerg,
the whole is a an impedance analyzer, not a low
end one though, as the changes to be measures are
minute. And the changes are biggest when the oscillator
oscillates.

Rene

 

[Fred Bloggs]

I am digging into a project requires a 10MHz crystal drives in vaccum

whereas the oscillator circuit oscillates at a 1 meter distance.


crystals terminals are connected to the signal and shield of a 1 meter
coaxial, rg316.


However my current colplitts design doesn't work now


1 meter rg316 coaxial
_______ . .... _______[op amp] __
| | |
| = (30pF) |
xtal |-------------------- | F.B.
| = (30pF)
|_______ ...... _____|


op amp is a HFA1130, non inverting config with gain about 2X


xtal intended to use as an inductor and oscillates with the 2x30pF
caps. and the feedback inserts in the mid way of the caps.


The design works OK with zero lenght, but doesn't work with a long
lead.


Does the phase delay / cap effect of the coaxial affecting the whole
matter. ?

Contrary to popular belief, the 1m length of cable at 10MHz is a simple
lumped element- but a gain swamping one at that. The RG-316 types run
~32pf/foot or about 100pf bulk capacitance in that 1m length, and at
Zo=50 ohms, the inductance comes in at 80nh/ft or 240nh over the 1m length.
http://www.dearborn-cdt.com/catalog/COAX-1.html

 

[Wes Stewart]

Hello,

I am digging into a project requires a 10MHz crystal drives in vaccum
whereas the oscillator circuit oscillates at a 1 meter distance.


crystals terminals are connected to the signal and shield of a 1 meter
coaxial, rg316.


However my current colplitts design doesn't work now


1 meter rg316 coaxial
_______ . .... _______[op amp] __
| | |
| = (30pF) |
xtal |-------------------- | F.B.
| = (30pF)
|_______ ...... _____|


op amp is a HFA1130, non inverting config with gain about 2X


xtal intended to use as an inductor and oscillates with the 2x30pF
caps. and the feedback inserts in the mid way of the caps.


The design works OK with zero lenght, but doesn't work with a long
lead.


Does the phase delay / cap effect of the coaxial affecting the whole
matter. ?

Yes. I scanned this thread quickly and don't think anyone mentioned
changing the oscillator type.

How about using a series resonant oscillator circuit? At resonance
the crystal will appear to be a fairly low value resistor and with a
bit of luck might even be close to the impedance of the coax, although
this isn't a requirement.

If you know the motional parameters you can calculate the effect of
the cable on the resonant frequency.

 

[Rich Grise, but drunk]

Hello Rich,


I was actually thinking about one, a little nuvistor tube. But I didn't
post to avoid being pelted.

Well, it might not work if the toob is still in its envelope - those frit
glass seals are proof against ordinary air, but I don't know what happens
if they try to keep vacuum out. ;-)

Thanks!
Rich
--
-----BEGIN GEEK CODE BLOCK-----
Version: 3.1
GAT(E P) dpu s: a++ C++@ P+ L++>+ !E W+ N++ o? K? w-- !O !M !V PS+++
PE Y+ PGP- t 5+++)-; X- R- tv+ b+ DI++++>+ D-? G e+$ h+ r-- z+
------END GEEK CODE BLOCK------