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:
- Measure the capacitance of the cable when it’s open (C) in farads (F).
- Short one end.
- Measure the inductance of the cable from the non-shorted end (L) in henrys (H).
- Impedance (Z) = √(L/C) in ohms (Ω).
It works for both coaxial cables and ladder line. Neat trick!