How to use a ferrite ring

Written by ken burnside Google
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How to use a ferrite ring
The cylindrical bump on the VGA cable on the right side of the image is a ferrite ring meant to block RF emissions from the VGA port. (connection cocnept - cables studio isolated image by dinostock from

Ferrite rings are used as EMI (electromagnetic Interference) dampeners on electronics devices, particularly those devices that are meant to send (or more commonly) receive radio signals. They also get used extensively in consumer electronics ranging from mobile phones to computers to minimise the radio frequency interference these devices can cause. Home computer enthusiasts sometimes put ferrite rings on motherboards, and radio controlled plane and boat hobbyists put ferrite rings on their planes.

Skill level:

Things you need

  • Wiring diagram for the device
  • Wire suitable for the device
  • Ferrite ring
  • Wire stripping tools
  • Electrician's tape

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  1. 1

    Identify, on the wiring diagram, where a receiver is likely to be, or, secondarily, where an EMI "hot spot" is likely to be (typically, receivers are isolated from other components, and EMI hot spots congregate around alternators, electrical motors and antennas.) For each of the places where a ferrite ring might reduce the electromagnetic interference of the device, do the following steps:

  2. 2

    Make sure the device is powered down, and that you've touched something to ground yourself.

  3. 3

    Strip the wire(s) with a wire stripping tool, and carefully cut the wire.

  4. 4

    Thread the wire through the ferrite rings.

  5. 5

    Splice the wire by braiding the strands together.

  6. 6

    Wrap the spliced wire and the ferrite ring with electrical tape.

Tips and warnings

  • Ferrite rings are one form of a category of device referred to as 'ferrite beads' or 'ferrite resistors'. Ferrite resistors and beads come in many configurations -- the benefit of ferrite rings is that rather than winding wire around them, you can thread the wire through them -- this makes them easier to install but doesn't get the same degree of benefit.

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