I've recently built this circuit: http://makerf.com/posts/mighty_simple_shortwave_transmitter
It works on the desired frequency as you can see from this video : https://www.youtube.com/watch?v=t6nFi7fdoK0 .
Now I'm trying to understand why and how it works, I would appreciate if you can guide me through the circuit in order to understand what each single components do.
This is what I think I've understood:
- The oscillation begins in the crystal (xtal) for the reason explained here What makes a crystal oscillation to begin
- There is a feedback loop which goes through the transistor Q1. Basically the RF is injected into the base and it gets amplified (and shifted by 180 deg?) by the transistor exiting from the collector.
- The L1 - variable capacitor is a tuned circuit but I don't understand why the collector is tapped there and in general what is its purpose.
- The L1 - L2 transformer is the way through the RF goest to the antenna and the transformer is required to adapt the impedance of the circuit to the 50 ohm required from the antenna
Finally, I'm not sure about the two resistor and the 0.05uF capacior.
Also, which oscillator circuit did inspired this design? Is it an Hartley Oscillator?
Thanks for your patience and if you have any good resource (book or website) which could help me in understanding oscillators, please let me know.