On Jan 20, 5:47 pm, Gary wrote:

The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.

I recall the article and have it around somewhere. The problem with
this (if you want to call it a problem) is it only works for a small
range of frequencies.

They do the reverse of this in AM broadcast antenna matching
networks (doghouses) where the object is NOT to have a variable
capacitor. A fixed, high-reactance capacitor is placed in series
with a 'tappable' inductor and the capacitor is 'tuned' by adjusting
the tap on the inductor. Again, works well at one frequency,
but not over an octave bandwidth.... K7JEB