Ohm rating on coax cables.

Discussion in 'General Electronics Chat' started by Nathan Hale, Jun 23, 2013.

  1. Nathan Hale

    Thread Starter Active Member

    Oct 28, 2011
    125
    2
    Hi Everyone! Hope all is well with u folks. I have a question about coax cables/ wires . I notice a lot of times that a coax cable of lets say 75 feet has a resistance rating of 50 ohms. What does the ohm rating mean? After all a wire is a wire and not a resistor. What is this resistance rating indicating?

    Thank you for all you replies.
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    That's 50ohm impeadance, it's not the resistance of the wire. This is determined by the inductance and capatcitance of the coax. Typically, the electronics' impeadance are matched at each end of the coax (aka transmission line)
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,344
    Hello,

    The resistance given is not the real resistance, but the impedance of the cable.
    This impedance depends on the diameter of the inner wire, the diameter of the shielding and the dielectricum in between them.
    More info can be found on this page of the EDUCYPEDIA:
    http://educypedia.karadimov.info/electronics/cablingrf.htm

    On the bottom of the page is the formula to calculate the impedance.

    Bertus
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    Impedance is a characteristic of AC circuits, and it has absoutely nothing to do with DC resistance. In addition DC resistance is a real number measured in Ohms. Impedance is a complex number whose MAGNITUDE is also measured in Ohms. It also has a phase angle measured in radians or degrees.
     
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