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I can make the bottom wider/over-coupled filter look similar to the top but it requires a lot of changes.
The Z of the 2-port ABCD is very different from the series 57 Ohm tlines.
Do you have the original L/C filter that was used to create these two filters?
There are multiple transformers in the library. If you need one with inductance, use mutual inductors.
The transformer with turns ratio is for simulating circuits where inductance is not needed.
Ideal transformer not right. Use transformer made up of mutual inductors instead.
You should never float nodes either. Voltage probe has infinite input Z.
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Qucs has a few Verilog-A PIN diode projects. You can also convert some Aplac or Spice PIN models into sub-circuits. How to get the parameters for a real life diode is problematic.
You can also model the diode as only two states, ON/OFF with Cp, Ls and Rs. That will be the easiest to do since the parameters can be found on the data sheet.
final schematic…
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You need to add a capacitor from R14 to ground called C2 so the OpAmp and transistor are biased properly.
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Why aren’t you using a real OpAmp like an LM324/358 designed for single rail operation and confirm the transistor and OpAmp are operating properly? You can confirm using DC or Transient analysis.
