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One of the first things I did when I first got my original TRS-80
(1978) was to write a simple QuickBasic program for calculation of the
LF inductance and SRF of unloaded coils, using Wheeler's approximations
for inductance and a lookup table interpolation of "Medhurst" data from
the fourth edition of the Radiotron Designer's Handbook. At the same
time I wrote a mutual inductance program based on the methods in
Circular 74, with the specific purpose of calculating coupling in TC's.
Later on I moved them over to my Mac SE and turned them into compiled
basic, then back into compiled basic on a PC. I suspect other guys used
the procedure earlier but never bothered to write about it.
Ed