[Elecraft] AADE LC meter for ham radio

[Ron D'Eau Claire]

I don't use the AADE meter (my inductance meter was scratch-built from the
ARRL handbook) but the fundamental frequency of the signal is not what the
inductor is reacting to in most modern designs 

The one I use, which I believe is similar to the AADE in measurement
methodology, applies a square wave to the inductance and measures the effect
of the inductance on the waveform. What is of importance is the frequency of
the leading and trailing edges of that square wave, which is many many times
the fundamental frequency of the waveform. The steeper the edges, the higher
their frequency. Graphically, consider the leading (or trailing) edge of the
square wave a part of a sine wave of some frequency. Following the steep
slope of the edge waveform, continue with it to draw a perfect sine wave.
You will see that the actual frequency of that sine wave may be somewhere
between 10 and 100 times the fundamental frequency of the square wave if
it's a decent square waveform.

That's the test frequency that the inductor is reacting to: the frequency of
the leading or trailing edge. 

Now, the fundamental frequency of the square wave can be of importance
because the measurement circuit often uses what happens to the waveform
during the time when the square wave is at peak or zero voltage to calculate
the inductance. The length of that time can affect the inductance value
reported, depending upon the design of the circuit, but that frequency is
NOT the "test frequency" the inductor is subjected to in the circuits that
I've worked with. 

Ron AC7AC