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Whats the thing on the wire ??

Discussion in 'Electronic Basics' started by [email protected], Aug 12, 2005.

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  1. Guest

    hi,
    i have noticed that several cables especially the ones used for
    communication, have a bulb like thing inbetween the wire. what is it
    used for ? i have it on the cable that i use for connecting MP3 player
    to PC. it is also there on the moitor cable. is this some sort of an
    amplifier or overvoltage protector or maybe some sort of spying
    device!!
    TY
    Braz -in -go
     
  2. Bob Myers

    Bob Myers Guest

    Generally, what you're describing is a toroidal ferrite "core" which
    has been placed around the cable (and then covered by the
    overmolding of the connector or an outer jacket placed over the
    cable assembly), and is intended for EMI (electro-magnetic
    interference) suppression.

    Spying device? You have got to be kidding....I hope...

    Bob M.
     
  3. One day Bob Myers got dressed and committed to text
    Hmmm, that said it wouldnt be a bad spot for such a device!! The average
    person is now used to seeing the ferrites.
     
  4. Rodney

    Rodney Guest

    It's used for noise suppression. Gives you a cleaner signal.
     
  5. It is a form of common mode inductor that suppresses radiated noise.
    It is made of permeable (allows a magnetic field through, much better
    than air does) ferrite. The cable passing through makes this into a
    transformer with as many 1 turn coils as there are conductors in the
    cable. The transformer is essentially invisible to any currents that
    pass both ways through the cable (in one conductor and back through
    another one), since their magnetic fields cancel. But any current
    that is trying to pass back and forth through the hole, in only 1
    direction at a time, has to pass through the inductance of a 1 turn
    coil through that amount of core. This impedance in series with these
    common mode currents reduces their magnitude, and also reduces the
    efficiency that a resonance can take place as a wave bounces up and
    down the wire, making the cable a less effective antenna. The exact
    location of the core on the wire can make a bog difference what
    frequencies are most effectively suppressed, so once testing
    determines the best place for the core (standing waves tend to produce
    current nodes and peaks at different places), it is often held at the
    correct place with a plastic overmold.
     
  6. Kitchen Man

    Kitchen Man Guest

    Yes!! It is a packet-sniffer, and is forwarding all your porn to the
    FBI!!!!!

    Or not. :)
     
  7. Bob Myers

    Bob Myers Guest

    Not really. The presence of a ferrite on these cables
    does very, very little to improve the signal quality, and
    more likely may result in some slight degradation (no, there
    SHOULDN'T be any added inductance appearing in
    the signal path, but then in theory, practice is just like
    theory - while in practice, of course, it's not...:)). It's
    an EMI suppression device, meaning that it's basically
    there to help hold down unwanted radiated emissions.

    Bob M.
     
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