Limitations of LC Filters 

Thank you. Between your videos and my NanoVNA I'm finally at a point where I can actually build useful filters.

Capacitors or inductors are essentially ideal constructions that do not exist in reality but are helpful to us in discerning capacitive and inductive behaviours. Theoretically, it is impossible to conceive and thus construct a capacitor without inductive elements and vice versa. Similarly, all conductors come endowed with a certain resistance and it is impossible to conceive a resistor without inductive or capacitive elements and vice versa. Perhaps we could introduce a more advanced approach to teaching electronics where we would only speak of reactive components of two flavours, primarily inductive or primarily capacitive, depending of their frequency response and therefore do away with the artificial and idealised distinction between capacitors and inductors. That might have practical benefits in designing better circuits by preventing certain unexpected and definitely unwanted behaviours in the end result.

Another excellent video. Complex reactance circuits really are, well, complex. 🙂 My old amateur radio brain kept trying to characterize antennas in filter characteristic terms. At first I thought it would be a simple paralell, with mostly scale as the difference. Then I wasn't so sure. 🤫...Then my brain melted, and I went and had a beverage.

really good stuff here - thank you very much.

A very good video (as always). You can explain complex topics in laymans words, thanks for that: I'm always learning so much from your video's. There i only very nitpicking thing: the "t" in your handwriting looks very much like a "f", I've always have to read twice.

2:35, but wikipedia states: "Inductive reactance X L is proportional to the sinusoidal signal frequency f and the inductance L"

Good basics. But in my life the “fun” starts, when I have to forget the fixed 50 ohms. I mean for example needing a broadband reject filter at 1 ohm impedance level or 10 kilo-ohm level. Or better yet, common mode noise filtering. In many cases, I have to “kill” the resonance in order to pass my (relatively) wide band signal accurately and eliminate wide band noise. Very high quality inductances and capacitances produce resonances as shown. My challenge is to utilize additional resistances as part of my filter, or select my ferrite that naturally has a very low Q. But while solving the resonance problem, I also need to avoid burning my added resistor with DC, for example. Most of my (analog) signals have to make it through unshielded twisted pair cables, or worse, untwisted multi wire cables and be subject to neighboring digital signals or switching power ripple/noise. As said, let the fun start!

Thank you Fesz for such informative videos. I learnt a lot of electronics by watching your videos and designed a low noise amplifier for my research product. It would be very helpful if you can help me in analysing my schematic and simulation results to further optimise the circuit for better results. Please reply

Choke use frequency around resonnance.

Thanks for another interesting video. Ferromagnetic materials have magnetic dipoles in them which will rotate all to the same direction as the externally applied magnetic fieldstrength increases. This externally applied field originates from a current through a wire wound around the magnetic material. At some magnetic field all dipoles are fully aligned and at that point the material is what we call saturated. The inductance drops at that point. This doesn’t happen in air coils. There are no magnetic dipoles in air. Exactly the same happens between class 1 and 2 ceramics in capacitors. Class 2 ceramics have electrical dipoles embedded in the material and these align with the applied electrical field up to a point (as the voltage increases) where all dipoles are aligned and the material saturates. These dipoles in the material, just as with magnetics, allow for much higher capacitance per volume but with a limitation. You can calculate charge Q in a capacitor by V times C. Do that over voltage using the C vs V graph and you will see that the charge ramps up and then goes flat, similar to the B/H curve of a ferro magnetic material. Class 1 ceramic material doesn’t have these embedded electrical dipoles and behave linearly like air in an inductor.

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