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Inductance at high frequency

Discussion in 'General Electronics' started by Jian, Nov 11, 2003.

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  1. Jian

    Jian Guest

    A system (straight wires here):

    ------------------ L

    ------------------ L

    Self-inductance of each is L (when alone),
    mutual inductance is M at low frequency.

    How do I obtain L(f) and M(f) from L and M for
    high frequency range, say, 100MHz?

  2. Robert Baer

    Robert Baer Guest

    What is the diameter of the wires?
    What is the spacing between the wires?
    How far away are they from a ground plane or ground planes?
    How long are they?

    In short, you must also consider capacitance, and other
    transmission-line effects.
  3. Jian

    Jian Guest

    What is the diameter of the wires?
    I know what you say. What I'm looking for is a good procedure
    to calculate the L(f) based on L and M (there are formula for
    straight wire, etc...). So, let's assume:

    wire radius: r
    distance: d
    length: l
    from ground: g
    they are all in a couple of cm range.
  4. Robert Baer

    Robert Baer Guest

    According to the Allied/Radio Shack Electronics Data Handbook
    (1970,1983), a parallel conductor line (ie: twin-lead) impedance is:

    Z0 = (276/sqroot(k)) * log(2D/d) where the dielectric coefficent of
    the surroundings is k, the wire diameter is d, and the seperation is D.

    That is all i can find so far.

    As a matter of note, if one makes a "gimmick" by twisting two wires
    together, one gets roughly one pF per inch.
    Obviously, the actual value will vary according to the insulation type
    and thickness, along with the wire size.
    Adding a ground plane will slightly decrease inter-wire capacitance if
    it is realatively close.
  5. GPG

    GPG Guest

    And the dielectric of the insulation. Basically unanswerable, unless you elaborate.
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