July 13, 2012

What is a ferrite bead?

Ferrite is a ceramic made from various iron and other ferromagnetic oxides.  A ferrite bead is considered an electric component which effectively acts as an inductor.  Ferrite beads are often used to reflect and absorb RF (which is dissipated as heat).  The frequency range that a ferrite bead absorbs depends on the material it is made from.

"Type 31" and "type 43" ferrite material are both very popular in amateur radio applications such as EMI noise supression and common-mode chokes.  Common-mode chokes are very useful devices that can improve the received noise level by blocking EMI travelling along power and telephone cables within the home.  Common-mode chokes can also help reduce the level of transmited RF travelling in common-mode on the shield of transmission cable and keep it out the home.  Additionally, common-mode chokes can reduce the level transmitted RF travelling into sensitive devices via power cables and cable TV lines.

Fair-Rite publishes an excellent technical paper, "How To Choose Ferrite Components for EMI Supressions".

Be sure to also see our related article, What is the schematic symbol for a ferrite bead? on NJ2X.COM.

NJ2X's built this Anderson Powerpole pigtail with a ferrite bead to supress EMI riding on the 12v DC line