Hi,

I've been thinking of getting some roller inductors to play with next time I
visit a hamfest, and it occurred to me that a generic roller inductor
doesn't have a linear change in inductance with roller position... does it?
E.g., at the half-way point you should get 1/4 the total inductance, right?

With a roller inductor the ratio of length to diameter is not
constant as the tapping point changes so the inductance is not
simply proportional to N^2. Using the standard handbook formula
(Nagaoka's), I get the inductance at the centre to be just under
half (44%) of that across the whole coil. Doubtless though, toward
the end, this formula becomes rather inaccurate.


Cheers - Joe G3LLV