Technical Articles

Inductor Selection: Manufacturers Part Numbers

Amateurs have long used the Amidon ( part numbering system for ferrite and powdered iron toroid cores. For powdered iron cores, the Amidon part number begins with a T and the following numbers are the outside diameter in hundredths of an inch.  The mix number follows after a dash.  For example, the T200–2 is a 2.00” OD, Type 2 powdered iron toroid core. Micrometals ( manufactures the Amidon powdered iron cores and uses the same part numbering system.

For ferrite cores, Amidon part numbers begin with FT and the numbering system is the same after that: FT68-61 is a 0.68” OD, Type 61 mix core. Fair-Rite ( is the original manufacturer of these ferrite cores and its part numbering system is entirely numeric. Digits 1 and 2 indicate product type (such as inductive or suppressive), digits 3 and 4 are the material type or mix, digits 5-9 are the core size code, and the last digit gives the coating type.  

More complete information about powdered iron and ferrite cores is available in the ARRL Handbook chapter on Component Data and References. ( Both the Fair-Rite and Micrometals catalogs are downloadable at no cost and provide a great deal of detail and background information.

Other Ferrite Products

In addition to ferrite’s inductive applications, it can also act like a resistor and dissipate energy as heat. This helps get rid of unwanted RF which is creating electromagnetic interference (EMI). DX Engineering offers a range of Ferrite RF Noise Reduction Kits, featuring combinations of toroids and snap-on beads designed for suppressing RFI in specific applications (linear amplifiers, AC/DC generators, HF base stations, and AM broadcast) or for general use. Also available are High Impedance Common Mode RF Choke Kits.

For more details on what is ferrite, what is a ferrite choke, and what is ferrite used for, click on these links to articles from OnAllBands.

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