[Elecraft] Measuring Inductors (was Re: [K2] Inductivity of Toroids)

[Jim Brown]

The right word is "inductance."  One of the most fundamental principles 
of electrical circuits is that "pure" components -- that is, a coil that 
has ONLY inductance, a capacitor that has ONLY capacitance, a resistor 
that his ONLY resistance -- do not exist in the real world.  All real 
components have "stray" electrical elements due to their physical 
construction.  Resistors have small values of inductance in their leads, 
and may have a tiny amount of capacitance in parallel.  If you measure 
at DC or at audio frequencies you won't see the inductance, but if you 
measure at higher radio frequencies you will see a higher value of 
impedance added by the inductance of the wire leads.

Inductors (coils) have some resistance in the wire used to wind them, 
and capacitance between the turns of the coil.  If you measure the 
inductor at low frequencies, you see only the inductance, and perhaps a 
small value of resistance. But if you measure at higher frequencies, the 
capacitive reactance and inductive reactance are in parallel but of 
opposite sign, so they partially cancel, and the apparent value of 
inductance increases. If you go high enough in frequency the inductive 
reactance and capacitive reactance will be equal, that's resonance, and 
the inductor looks like a high value resistor. Go even higher in 
frequency and that inductor looks like a capacitor.

Recent editions of the ARRL Handbook have an excellent discussion of 
these concepts, and are a great place to learn electronics concepts. 
Thank Ward Silver, N0AX, editor of recent Handbooks for his clear, 
easily understood style of technical writing.

73, Jim K9YC

> Though I closely adhered to the manual, the measured inductivities are 
> almost twice as high than the values stated in the manual (on the 
> parts list in appendix A).