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THE AM BULLETIN BOARD => Technical Forum => Topic started by: WA2SQQ on March 28, 2021, 12:55:39 AM

Title: Interesting filter design video
Post by: WA2SQQ on March 28, 2021, 12:55:39 AM
Interesting video on filter design. Iíve not seen this design before. Iíve been following this guy for some time. Daily short videos that are very informative. Heís a ham, but I donít know his call. Anyone know how to model his design in Spice?

Title: Re: Interesting filter design video
Post by: M0VRF on March 28, 2021, 04:17:27 AM
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'


Title: Re: Interesting filter design video
Post by: ka1bwo on March 28, 2021, 10:47:15 AM
 Evaluate the inductor by making a S21 measurement with a VNA. Then apply it to spice.   

Title: Re: Interesting filter design video
Post by: Tom WA3KLR on March 28, 2021, 02:02:35 PM
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.
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