I'm experimenting with the Colpitts oscillator, configured in the common base topology. Here is a picture:
In my own circuit, the coil is approximately 20 microhenry, and I've experimented with several values of capacitors ranging from around 10pF to 1nF.
I understand that the coil and the capacitors form a resonant circuit which has the output fed to an amplifier (here a common base amplifier). I also understand how common base amplifier works.
From oscilloscope measurements I've noticed that changing the resistor between the emitter of the transistor and ground (R1 in the picture) to a smaller value dramatically increases the amplitude of the oscillation. But I can't understand the reason for this!
Even though I understand resonant circuits and transistor amplifiers separately, I somehow fail to see exactly how the resistor affects the amplitude of the oscillation. In the common base configuration, the emitter is the input and the collector is the output. If we lower the emitter resistor resistance, more current would (according to my reasoning) somehow bypass the second capacitor.. And higher the voltage across the resistor, higher the input to the amplifier and therefore higher amplified output. But how does this all work? This could be a very simple thing but I've been trying to make sense of this all day but I still don't really understand why lowering the emitter resistor increases the output amplitude. I've also looked at the common base amplifier gain formulae but they all just show a collector resistor (which is not even present at this circuit).