Bill Turner wrote:

On Tue, 9 Dec 2003 19:20:25 -0500, "Ralph Mowery"
wrote:

The inductance is not changing. What you are measuring is not pure
inductance but the coil has a stray capacitance. That is what is making the
coil seof resonate.

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I am well aware of that, but you are tap dancing around the relevance of
the formula X=2*pi*F*L.

Just answer this: If I have a coil of very high Q (no appreciable
resistance), and I apply 100 volts of 100 MHz AC to it, and measure a
current of 2 milliamps through it, then:

1. What is its reactance?
2. What is its inductance?

Its impedance has been measured to have a magnitude of 50,000 ohms.
If you have independent information that its Q is very high, you can
assume that this impedance is made up of some combination of inductive
reactance and capacitive reactance. With a single measurement such as
this, that is about all you can say.

It cannot be assumed to be all inductive reactance (or any particular
combination of inductive and capacitive reactances), just because
someone labeled the device as an inductor or because it looks like a
coil. Other measurements are needed to nail the details.

A parallel resonance with 50,000 ohms impedance (at some frequency) is
not the same thing as an inductance with 50,000 ohms of inductive
reactance (at the same frequency). They pass a similar magnitude of
current at that frequency for the same applied AC, but their current
phases do not match. And their reaction to nonsinusiodal waveforms is
very different.

--
John Popelish