The AM Forum

Interesting video on filter design. I’ve not seen this design before. I’ve been following this guy for some time. Daily short videos that are very informative. He’s a ham, but I don’t know his call. Anyone know how to model his design in Spice?

https://youtu.be/1aYp-RNpHDA

Looks like the response of a elliptical filter. However there is loss in the passband which is unacceptable. Looks like winding the 2 inductors on the same former simulates the parrallel capacitance normally associated with elliptical filter by using stray/coupled capacitance of the proximity of the 2 inductors. I don't see the point in investigating it any further, it may be novel but the response won't be optimal and will be a pita to tune.

Interesting tho'

JB.

 Evaluate the inductor by making a S21 measurement with a VNA. Then apply it to spice.   

I hadn't used LTSpice in so many years I had to delete it and re-install to get the latest version. I simulated his original 2 section lumped inductor pi filter using his capacitor values and since the inductors are stated as 15 turns only (both the same value) I re-ran the simulation and changed the inductance value until I got a nice 40 meter low-pass filter response using 1.47 uH inductors. As I presumed, the current in the two inductors is different by 108 degrees at 7.3 MHz. so I don't see how his version is going to work well. 20 meters was down 22 dB (no losses in the simple parts simulations). BUT I have not taken the time to try his transformer (mutual inductors) version yet.  

I haven't done this in many years, but as I recall to define a transformer in LTSpice, you have two inductors with a coupling constant.  A 1:1 transformer is modeled as both inductors same inductance value and say a coupling coefficient of 1, statement/Spice directive:   K1 L1 L2 1.