Ferrites

Discussion in 'General Electronics Chat' started by Screamtruth, Jul 10, 2006.

  1. Screamtruth

    Thread Starter Member

    Apr 17, 2006
    10
    0
    Can anyone explain the theory behind the usage of ferrite cores on VGA cables? I know that they are utilized for noise reduction, but I would like to understand the details on how this is working. How would the introduction of a magnetic object serve as a "filter", and I assume that this can also load the signals in the cable.

    Thanks,
    Out.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    You are correct that ferrites are magnetic materials. They used to be used as memory devices. Depending on the direction of current through them, they magnetize in different directions.

    As noise filters, they never get to saturation. They pull energy from the signal as they magnetize. The individual ferrite's characteristic permeability and size makes it sensitive to ranges of frequencies. There is an upper limit to the signal frequency in a VGA line, so a ferrite bead used as a noise filter would respond to higher frequencies. The action is like a hash filter choke, where so much work is done building the magnetic field that high frequencies are sharply attenuated.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Here is a link to brief application note explaining the basic operation of a ferrite beads.

    http://www.ferronics.com/catalog/beads.pdf

    Hopefully it will give you better feel for the concept of noise filtering using ferrites.

    hgmjr
     
  4. Screamtruth

    Thread Starter Member

    Apr 17, 2006
    10
    0
    Thank you for the input; very helpful.

    Take it easy,
    Nathan
     
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