Ok well today’s task went to shit. I was going to start measuring all these crystals. Managed to get nowhere. Went for an amble, did some shopping and generally got sod all done.
Reminder: Discord this UTC evening
I also need to measure the motional parameters of 2-300 crystals, mostly form Golledge and Russia, but I've hit the following snag, the bloody Colpitts oscillator (the one with switchable series cap for determining ser/par resonance) it overloads the crystal (almost 9Vpp ) and creates a huge short term frequency instability, and I want to get them into 10-20Hz tolerance pools for my filters, combined with the fact that they're freaking ultra sensitive to temperature (if you touch them with your hand while inserting in the socket, they drift, I needed to use a plastic SMD tweezers) makes life miserable .
Does anyone have an idea of an oscillator that loads the crystal a bit less ?
Thanks,
DC1MC
Why dont you measure them in an IEC444 test fixture on a VNA ?
If it needs to be measured in an oscillator, the following caveats apply:
- never overrun maximum crystal power (thats a few ten microwatts, normally). Reasons: Nonlinear effects (pulling), heating,
in worst case electrode damage, permanent frequency change or death.
- Your oscillator needs limiting. Simple way: Schottky diode from AC base to ground.
Better: power regulator. Pick off Colpitts output, use AD8307 log detector and op amp regulator to drive base bias.
Advantage: power level can be accurately chosen and stabilized.
Regards, 73
Wolfgang DL1DWG