Bill, it's one thing to say a coil's reactance is non-linear, but it's
another to assert its inductance varies with frequency.

Both statements are true and easily provable. A simple air core coil
which measures one microhenry at a low frequency may have an inductance
of several millihenries (or even henries) when near its self resonant
frequency. It's a simple law of physics; there is no way around it.
And *above* the self-resonant frequency, the choke actually behaves like
a capacitor, believe it or not.


As I responded
before, the inductance of air coils varies very little with frequency.

That statement is true only at relatively low frequencies. Get near the
self-resonant frequency of an air core coil and you'll find otherwise.
Designers using relatively large coils over a wide frequency range run
into this problem all the time. As I mentioned in another post, the
classic example for Amateur Radio is the plate choke in a tube type
amplifier. Designing such a choke that has enough inductance to work
over the entire HF spectrum without self-resonances is nearly
impossible. Many amplifier designers don't even try; they just switch
inductance in and out of the choke depending on frequency.


Youall seem to be hitting all around the 'problem'. A coil has 3
components, the resistance of the wire, the inductance, and the stray
capacitance. As the frequency is changed from DC to low AC to RF each
component has more or a less effect on how it acts in a circuit. The actual
value of each does not change, just the effect on an external circuit.

For small coils at DC the reisitance is the major item that will be seen by
an external circuit. At low to medium frequencies the inductance will be
the major factor. At very high frequencies the capacitance may be the major
factor. At self resonant frequencies , the tuned circuit effect takes
over.