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

Very interesting. This is what I used to use:
https://www.mulvey.us/Coil_Winding_Data_opt.jpg
I still have the book. Radio Shack Electronics Data Handbook also has 
formulas for more complex coils.

Allen Mulvey


On 7/23/2025 10:56 AM, RussellMc wrote:
> 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