Toroids, RF-Cores

by Tony van Roon

Toroids & RF-chokes, come in different shapes and sizes, like in donut, tube, and stick models, and are used on a large scale in a variety of electronic equipment. Toroids can be of different materials, like Ferrite or Iron. The most common applications today are filtering, and transformers. If you check your cable at the back of your computer monitor you will find one, or even two, on the cable going to your computer. They are also used in Power Supplies, Radio, Ham Radio, Scanners, Transmitters, Transformers, and Electro-Magnet applications.
Here is an excellent link to provide more 'Amidon' information: Bytemark Inc.

Below I have made up 4 tables with the most common-size toroids. I hope they can be of some assistance to you. The µ stands for the permeability factor of the core. All measurements are given in 'inches'. I don't have or know the info in mm (metric) so don't ask.

Red E Cores

Iron Powder Properties:
Material  Basic-powder  Permeability (µ)  Freq.Range (MHz)  Color-Code
   0        Phenolic         1               100 - 300        Tan
   1        Carbonyl C       20              0.5 - 5.0        Blue
   2        Carbonyl E       10              2.0 - 30.0       Red
   3        Carbonyl HP      35             0.05 - 0.5        Gray
   6        Carbonyl SF      8                10 - 50         Yellow
   7        Carbonyl TH      9               5.0 - 35.0       White
   10       Carbonyl W       6                30 - 100        Black
   12       Synthetic Oxide  4                50 - 200        Green/White
   15       Carbonyl GS6     25             0.10 - 2.0        Red/White
   17       Carbonyl         4                50 - 200        Blue/Yellow
   26       Special          75           LF Filters,Chokes   Yellow/White

*Non Linear: Material #17 was developed as a temperature stable (50) alternative to the #12 (170). Frequency ranges shown are for best 'Q'/Useful over broader frequency ranges with lower 'Q'.

Toroid used with Ham Radio

The photograph at left shows a Toroid Red 'E' Iron core
and is used in a QRP CW-transmitter (morse-code) application
in the 30-meter band.