Given xtal specs can a Colpitts oscillator component values be successfully modelled??

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Chris Wilson

Joined Dec 2, 2011
14
Given xtal specs can a Colpitts oscillator component values be successfully modelled?? I have changed the oscillator part of a rock bound LO on a software defined receiver to work with a crystal of 461.5 kHz fundamental using values fro C10, C11 and C12 from a US user, with a different make of xtal. Note the new component values printed at the TOP of the schematic please! His starts and runs reliably. Mine sometimes needs me to touch or fiddle with the pcb to get it going. I have managed to track down the full spec of the new old stock xtals I have, is this sufficient for someone to model it please? I am a newbie well out of his comfort zone, so please make it as simple as possible to understand! Googling suggests modelling such xtal controlled oscillators is a bit fraught, not that I would know where to start with the likes of SPICE....
 

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Dodgydave

Joined Jun 22, 2012
9,644
If you have to Fiddle it to get it to kick up, then your capacitance is too small or too large for the xtal, try changing the values of C 10,C11.
 

Alec_t

Joined Sep 17, 2013
11,738
Given xtal specs can a Colpitts oscillator component values be successfully modelled?
The pdf file is very general and gives insufficient data for an accurate Spice model to be built for a specific crystal frequency. An inaccurate model seems pointless for your purpose.
 

Thread Starter

Chris Wilson

Joined Dec 2, 2011
14
The pdf file is very general and gives insufficient data for an accurate Spice model to be built for a specific crystal frequency. An inaccurate model seems pointless for your purpose.

It need not oscillate on a specific fundamental frequency, so long as it is stable, my usage is the LO for an SDR receiver and I can offset any reasonable LO close to the fundamental. Thanks for the replies, will carry on fiddling! I'll alter C10 and C11 as suggested, cheers.
 
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