I have tried breadboarding a simple Colpitts oscillator, just to see how it works (and to get to use my 'scope for something more interesting than measuring static voltages).
I have been following this example, specifically the second circuit design:
I'm feeding it 5 V, the resistors are all at 1k, L is a .22 µH fixed inductor, Q is a 2N4401, C1 and C2 are .001 µF ceramics and the unlabeled cap at the base is a 220 pF ceramic (maybe way too low?), and I'm probing between emitter and ground.
Now, admittedly, these values are more or less randomly chosen from my component drawers. In this case I am not interested in obtaining a specific frequency as long as it's low enough for me to measure it (50 MHz), so I figured I could just throw in any values for the caps and the inductor, as long as they were high enough - I've read that this can actually be a pretty accurate method of measuring capacitance and inductance respectively, based on the frequency you get.
- Why is the circuit not oscillating? I'm measuring a DC voltage of 1.87 V at my probe point.
- How do you calculate the proper resistor values (or ratios)?
- What's the base cap used for? Just power decoupling?
- Am I probing in the right place?