I can't for the life of me figure out how the following SAW oscillator works. I can't see how the oscillation would be maintained since it doesn't use a feedback mechanism I'm familiar with. This post could prove useful.
So here is what I was thinking:
- L2 blocks high frequency components from coupling back to the power supply, though I'm not sure why this would happen (150nH from dimensions given).
- C3 is a supply bypass cap, which likely has something to do with L2 though I'm not sure what. On some boards this doesn't seem to be populated (unknown value).
- L1 presents a high impedance at the oscillation frequency (35nH from dimensions given).
- T1 is an RF transistor in a Class C amplifier configuration.
- R1 sets the transistor bias and possibly the transmit power.
- R2 and T2 enables the circuit.
- C2 presents a low impedance path to the antenna to remove the DC component (unknown value).
I'm not sure what C1 is for, and it seems to be unpopulated on some of the boards. For the SAW resonator, the only thing I can think is that when turned on it rings for a bit then dies down, so continuous transmission wouldn't be possible.
I'm hoping someone could shed some light on my assumptions listed above, and maybe on how the component values were selected.