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 Qvalue
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 Qvaules 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.
