The characteristic impedance of a cable (it was coaxial cable I was interested in) is, as far as i know, its high frequency impedance (if we supply the line with some signal, the line draws some current from the source and the ratio voltage/current defines the characteristic impedance of the...
Why does a wave reflect when it meets an impedance discontinuity? And why is there a 180 degrees phase shift of the reflected wave when the transmission line finished with short circuit and no phase shift when the far end of the line is opened?