The art of homebrewing is one the many exciting aspects of Amateur Radio. As I have ventured on my journey I have come across countless articles and schematics of beautiful and simple radios. One in particular was the One Watt Transmitter in a Kodak Film Box (QST, October 1994, PG 64ff). As I read the article and look over the schematic I found I would have only one problem. The inductor L1 was to be wound on a T37-2 toroid. Now I knew what a toriod was, I understood wrapping it with wire, but somehow that was not enough. I wanted to know how to design my own toroids. I began searching the internet for any information and found very little helpful guidance in the WWW lands. I then turned to my trusty ARRL Handbook for Amateur Radios (both the 1966 and 2000 revision.) Much to my dismay I found very little help in either. So off to the public library I went. At last, the answer to my delemma. In "Secrets of RF Circuit Design 2nd Edition" by Joseph J. Carr amd "Radio Handbook 23rd Edition" by William I Orr, W6SAI I found what I was looking for, How to Roll Your Own Inductors.
Toriod Designations can be determined by XX-YY-ZZ where:
XX - FT or F for Farrite
XX - T for Iron
YY - The outside diameter in 100th of an inch.
ZZ - The material used.

For Example an FT-50-43 Toroid would be a ferrite powder toroid core with an outside diameter of 1/2 inch made from material type 43.

All manufactures list an A_L constant with each type of toroid. With this number you can determine the number of winding needed to achive a specific value. An example of this would be the T-50-0 with an A_L of 320. Once you know the A_L you can just plug it into the formula # of Turns = 100 * Sqrt(µH/A_L) for an Iron Powder Toroid or # of Turns = 1000 * Sqrt(mH/A_L) for a Farrite Powder Toroid.
When winding a toroid, always wind the wire so that the windings are evenly space around 330º of the Toroid. This will leave 30ºs of seperation for mounting the toroid.
If you wish you may download the Microsoft Excell file Toroids.xls which contains all the data listed on this page. Right click on the file name above and chose "Save Target As...".

Ferrite Powder Toroids Cores

Type Description

33 M-Z. Used over .001 to 1Mhz for loopstick antenna rods. Low volume resistivity<

43 N-Z. Medium wave inductors and wideband transformers to 50Mhz. High attenuation over 30 to 400Mhz. High volumn resistivity

61 N-Z. High Q over 0.2 to 15 Mhz. Moderate Temperature stability. Used for wideb and transformers to 200 Mhz

63 High Q over 15 to 25 Mhz. Lower permeability and high volumn resistivity.

67 High Q operation over 10 to 80Mhz. Relativily high flux density and good temperature stability. Is similar to Type 63, but has lower volume sensitivity. Used in wideband transformers to 200Mhz

68 N-Z. Excellent termerature stability and high Q over 80 - 180 Mhz, High volume resistvity.

72 High Q to 0.50 Mhz, but used in EMI Filters from 0.50 to 50 Mhz. Low Volume resistivity.

75 Used in pulse and wideband transformers from 0.001 to 1 Mhz and in EMI Filters from 0.50 to 20 Mhz. Low colume resistivity and low core losses.

77 0.001 to 1 Mhz. Used in wideband transformers and power converters, and in EMI and noise filters from 0.50 to 50 Mhz.

F Is similar to Type 77, above, but offers a higher volume resistivity, higher initial pereability, and higher flux saturation density. Used for power converters and in EMI/noise filters from 0.50 to 50 Mhz.

Iron Powder Toroids Cores


0	Used up to 200 Mhz. Inductance varies with method of winding.
1	made of Carbonyl C. Similar to Mixture No. 3 but more stable, and has a higher volume resistivity.
2	made of Carbonyl E. High Q and good volume resitivity over range from 1 to 30 Mhz.
3	Mode of Carbonyl HP. Ver good stability and good Q over range of 0.05 to 0.50 Mhz.
6	Made of Carbonyl SF. Is similar to mixture #2, but has higher Q over range from 20 to 50 Mhz.
10	Type W powderer iron. Good Q and high stability from 40 to 100 Mhz.
12	Made of synthetic oxide material. Good Q but only moderate stability over the range 50 to 100 Mhz.
15	Made of Carbonyl GS6. Excellent stability and good Q over range 0.1 to 2 Mhz. Recommended for AM BCB and VLF applications
17	Carbonyl material similar to mixture #12, but has greater termerature stability but lower Q than #12.
26	Made of Hydrogen Reduced Iron. Has very high permeability. Used in EMI Filters and DC Chokes.

Last Updated Jan 28, 2003

Type	Description
33	M-Z. Used over .001 to 1Mhz for loopstick antenna rods. Low volume resistivity<
43	N-Z. Medium wave inductors and wideband transformers to 50Mhz. High attenuation over 30 to 400Mhz. High volumn resistivity
61	N-Z. High Q over 0.2 to 15 Mhz. Moderate Temperature stability. Used for wideb and transformers to 200 Mhz
63	High Q over 15 to 25 Mhz. Lower permeability and high volumn resistivity.
67	High Q operation over 10 to 80Mhz. Relativily high flux density and good temperature stability. Is similar to Type 63, but has lower volume sensitivity. Used in wideband transformers to 200Mhz
68	N-Z. Excellent termerature stability and high Q over 80 - 180 Mhz, High volume resistvity.
72	High Q to 0.50 Mhz, but used in EMI Filters from 0.50 to 50 Mhz. Low Volume resistivity.
75	Used in pulse and wideband transformers from 0.001 to 1 Mhz and in EMI Filters from 0.50 to 20 Mhz. Low colume resistivity and low core losses.
77	0.001 to 1 Mhz. Used in wideband transformers and power converters, and in EMI and noise filters from 0.50 to 50 Mhz.
F	Is similar to Type 77, above, but offers a higher volume resistivity, higher initial pereability, and higher flux saturation density. Used for power converters and in EMI/noise filters from 0.50 to 50 Mhz.