Finding the characteristic impedance of an antenna cable

I recently stumbled on a cool video that showed how to compute the impedance of an antenna cable. Unfortunately it’s almost five minutes long, so I thought I’d summarize:

  1. Measure the capacitance of the cable when it’s open (C) in farads (F).
  2. Short one end.
  3. Measure the inductance of the cable from the non-shorted end (L) in henrys (H).
  4. Impedance (Z) = √(L/C) in ohms (Ω).

It works for both coaxial cables and ladder line. Neat trick!

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