[Elecraft] Toroids

[Charles Greene]

Trev,

At 10:18 AM 6/3/2002 +0100, you wrote:
>With all the talk about toroids and baluns recently I decided to rifle 
>through the junk box looking for suitable cores.  It appears that I have 
>plenty of all shapes and sizes but I have no idea of their individual 
>properties.  Is there any way of identifying these unmarked devices so I 
>can put a few to good use?

Well, here's the way I do it.  First you need a book or chart of Al vs size 
and material.  I use the Bytemark (formerly Amidon) data book, but there's 
some other sources.  Then I wind a few turns of enameled wire, size is not 
important.  I usually use #18 or so.  Then measure the inductance using a 
LCR meter or an antenna analyzer if it will measure inductance L.  If I 
guessed wrong and the reading is beyond the scale of the meter I am using, 
I change the number of turns until I can get a good reading.  Then plug in 
the formula for inductance you will find in the data book or source of Al 
values and solve for Al.  Now with a value of Al and size, consult the 
table of Al values and you can usually identify the material.  If the 
material or size is a discontinued item, use the nearest one.  Better yet, 
now that you have the Al value, you don't need anything else to calculate 
how many turns you need for X inductance.  You just need the material to 
determine whether it is suitable for your application.

If some one has a simpler way, I'm listening.


73, Chas, W1CG