I have measured the impedance of the LC tank circuit which I referred on my last entry.

The configuration of the circuit is exactly the same as that time.

In order to observe the impedance, by using Koji's technique I injected a RF signal into the output of the resonant circuit.

In addition I left the input opened, therefore the measured impedance does not include the effect of the transformer.

- - - - - - - - - - - - results

The measured impedance is attached below; "LCtank_impedance.png"

The peak around 50MHz is the main resonance and it has impedance of ~1500 [Ohm], which should go to infinity in the ideal case (no losses).

In fact the impedance looked from the input of the circuit gets reduced by 1/n^2, where "n" is the turn ratio of the transformer.

By putting the n=4, the input impedance of the circuit should be 93 [Ohm]. This is a moderate value we can easily perform impedance-matching by some technique.

I also fitted the data with a standard model of equivalent circuit (see attachment 2).

In the figure.2 red component and red letter represents the design. All the other black stuff are parasites.

But right now I have no idea the fitted value is reasonable or not.

For the next I should check the input impedance again by the direct way; putting the signal into the input.