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

On Thu, Jul 24, 2025, 4:39 AM Allen Mulvey <[email protected]> wrote:

> 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.
>

Very interesting.
>
The first formula please identical to the one that I have remembered for
decades.
The others are similar to the one in that article that I cited and I
haven't seen them until recently.

>
>
>      Russell
>
> 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
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