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characteristics impedence

Discussion in 'Electronic Basics' started by mahak, Nov 24, 2007.

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  1. mahak

    mahak Guest

    hi all,

    can anybody plz tell how do we measure cahracteristic impedence of a
    cable, may it be coaxial, stp, utp or power looks impedence
    matching and trying to get the maximum power. i s there any other way?
  2. Tom Biasi

    Tom Biasi Guest

  3. Eeyore

    Eeyore Guest

    Well, you can safely forget about the concept for an equipment power cable.

  4. john jardine

    john jardine Guest

    Just measure it.

    1] Measure the "L" with the lead ends short circuited.
    2] Measure the open circuit "C"
    3] Then Zo= square root of L/C

    Some I did last year ...
    2mtr of "75ohm" coax L=1.48uH C=146pF ... Zo=100ohm*
    2mtr of 50ohm coax L=0.83uH C=168pF ... Zo=70ohm
    2mtr of 'twin flex' L=1.23uH C=70pF ... Zo=132ohm
    2mtr of 'mains cable' L=2.84uH C=281pF ... Zo=100ohm
    3mtr CAT5 patch cable L=2.51uH C=157pF ... Zo=126ohm

    (measured twice, still same result!)
  5. Phil Allison

    Phil Allison Guest

    "john jardine"

    ** Likely the frequency you used for the L and C measurement was not in the
    normal RF range.

    Zo for co-ax tends to rise at low RF and audio frequencies.

    ........ Phil
  6. Rich Grise

    Rich Grise Guest

    I would either look it up in the cable spec, calculate it, or measure
    it with a TDR.

    Good Luck!
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