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oscillator design with long crystal lead

E

E Minor 7

Jan 1, 1970
0
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. ?

Thanks for great help

EMinorSeven
 
J

Joe McElvenney

Jan 1, 1970
0
Hi,

Your ASCII art didn't come over very well but I'd guess that
you have too much capacitance across the crystal. Try removing the
30pF's and rely on the capacitance of the coax alone (a metre of
50-ohm is about 22pF). It won't be very elegant but with
semi-rigid stuff that might not matter if you don't move it around
too much.


Cheers - Joe
 
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