To design a new resonant EOM box I started reviewing the prototype that I've built.
As a part of reviewing I checked an important thing that I haven't carefully done so far :
I compared the measured input impedance with that of predicted from a circuit model. I found that they show a good agreement.
So I am now confident that we can predict / design a new circuit performance.
* * * (input impedance) * * *
Performance of a resonant circuit is close related to its input impedance and hence, in other words, determined by the input impedance.
Therefore an investigation of input impedance is a way to check the performance of a circuit. That's why I always use impedance for checking the circuit.
The plot below is a comparison of input impedance for the measured one and one predicted from a model. They show a good agreement.
(Note that the input impedance is supposed to have 50 Ohm peaks at 11, 29.5 and 55 MHz.)
* * * (circuit model) * * *
To make the things simpler I assume the following three conditions in my model:
1. inductor's loss is dominated by its DC resistance (DCR)
2. capacitor's loss is characterized only by Q-value
3. Transformer's loss is dominated by DCR and its leakage inductance
All the parameters are quoted from either datasheet or my measurement. The model I am using is depicted in the schematic below.
Basically the Q-vaules for the capacitors that I used are quite low. I think higher Q capacitors will improve the performance and bring them to more 50 Ohm.