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[Joe Gwinn]

Yes, mathematically true for sure. But I like the phase view as well. For one example, on the resonances of crystal resonators, one will see...

[Joe Gwinn]

Well, that's pretty clear. The main resonance is at about 8 KHz (where phase crosses zero). There are little parasitic resonators causing for...

[Joe Gwinn]

I'd compute the Arc Tangent of the imaginary impedance divided by the real part. This may show all the resonances clearly....

[Joe Gwinn]

My venerable function generator (bought in 2004) broke yesterday, so there will be a delay while I get a new generator. I'm tending towards the Rigol model...

[Joe Gwinn]

Given that that inductance variation is not linear with frequency (it may be square root though), I think that the easiest approach is iterative...

[Joe Gwinn]

Yes.




As requested by Helmholtz, I will apply Terman's method to my test pickup, and will report the results...

[Joe Gwinn]

But there is that nice big sheet of copper-plated mild steel right there, oriented perfectly to support an eddy-current image of the coil winding...

[Joe Gwinn]

Have not yet done that, for lack of a comparison.




But they do affect the apparent inductance, which figures...

[Joe Gwinn]

Well, I've been quiet for a reason. Brad Burt (Classic Amplification) lent me his Hantek 1833C for testing, just as he did with a DE-5000 unit in 2015, with...

[Joe Gwinn]

That LT Spice model is equivalent to adding another series resistor to model the eddy-current loss. The problem is the use of a fixed resistor...

[Joe Gwinn]

That's good to know.

While LT Spice is very useful, it assumes lumped-parameter circuits, and thus cannot directly describe eddy...

[Joe Gwinn]

Many people on this group will want those explanations....

[Joe Gwinn]

It looks like there are two extra resonances around 150 KHz. A phase plot will locate the resonances precisely - in a low-Q inductor like a...

[Joe Gwinn]

That's right. I think I was the original source of that pdf, but where is the second page?...

[Joe Gwinn]

So the theory revolves around extra resonances. This can be seen most clearly in a phase plot.




The ratio...

[Joe Gwinn]

I'm confused. I thought we were talking about those pickups that yielded about 500 pF of capacitance well above 10 KHz.


...

[Joe Gwinn]

Main peak is at 10 KHz or so. I bet that Terman's method will get the correct self-capacitance, because it will never see all that business...

[Joe Gwinn]

Ahh. OK.



I would think that it would be worthwhile to dig into a unit showing such an implausible capacitance....

[Joe Gwinn]

So, we do have lab validation.

In the values provided by the various methods, do the errors of one compared to another method...

[Joe Gwinn]

Aren't we going in circles here? Eddy currents in the nearby metal causes the inductance to vary with frequency, and inductance cancels capacitance,...

[Joe Gwinn]

Well, the inductance is involved in the computation, because inductive reactance cancels capacitive reactance, both varying with frequency....