Below is a schematic of an amplifier. The inductor used is a 1 μH inductor, emitter resistor is 2.2 kΩ. The bias resistors are both 200 kΩ. The capacitors are both 1 μF. I am planning to design a matching network to match it to a 50 Ω load and test it with a signal generator. How should the output impedance be calculated? I am planning to use this circuit as a buffer for a hartley oscillator.
Here is what I was thinking for calculating the equivalent output impedance (L is connected to ground):
Your transistor model claims that the transistor output side is an ideal current source. The only output side impedance is inductor L. If you for some still unknown reason absolutely want that the output impedance of the amp with JUST EXACTLY THIS transistor is 50 ohms, put a 50 ohm resistor in parallel with the inductor.
Use so high inductance that inductor's reactance is much higher than 50 ohms. Or insert a parallel capacitor with the inductor, select the capacitance so that together they are a resonant circuit at the operating frequency. The remaining output impedance is the inserted resistance in parallel with the resonant circuit.
I wouldn't waste RF power to the inserted resistor, but that's your way, selected by you when you decided the unreaalistic equivalent circuit of the transistor and started to want 50 ohm output impedance. I would worry how to make my load such that it doesn't reflect the signal back and how to make my amp to deliver what's expected to be got to the load. If the load reflects anyway, the amp should be made robust enough to tolerate the reflected wave. I would also worry how to either keep the amplification free of distortion or how to achieve a high energy efficiency and how the filter out the distortion frequencies. And all this with practical transistors.
