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:
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.
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'.
Here is a good link for more information and dimensions (including metric) on toroids: TOROID DIMENSIONS
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.
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Copyright © 1999, by Tony van Roon
Last updated May 12, 2010