oscillator design with long crystal lead

Apr 12, 2006 1 Replies
E

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



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J

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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