[EE]:: Inductance formulae - 1928 source, 2 versions I hadn't met and some glorious 97 year old advertisements.

Actually useful.
To calculate inductance of single layer inductors I use a formula I came
across 50++ years ago.

         L = a^2 x N^2/ (9a + 10b)

a = coil diameter in inches
b = coil length in inches
N = turns
L in uH.

I knew this was old when I acquired it but today went looking for the
source.
It's from an October 1928 "The Institute of RAdio Engineers" journal, vol
16 number 10.
The ads alone make it worthwhile.
He shows a more precise formula. the one I knew, and one for thin layered
coils.

Page 140-142 here
(= pages 1398 - 1340 in the original)


https://www.worldradiohistory.com/Archive-IRE/20s/IRE-1928-10.pdf

Change the "10" to see other months.
Full index in  volume 12
          https://www.worldradiohistory.com/Archive-IRE/20s/IRE-1928-12.pdf

Scribd copy of just the article here

https://www.scribd.com/doc/309709664/Simple-Inductance-Formulas-for-Radio-Coils



                Russell