Characteristic Impedance
Characteristic impedance is the voltage-to-current relationship of a travelling signal in a transmission line.
It depends on the cable’s electrical geometry and materials. It is not the same as DC resistance measured through the conductor or across an unplugged connector.
Characteristic Impedance — S/PDIF Cable
For an electrical coaxial S/PDIF cable, the intended transmission line is a 75-ohm system. Matching the cable and connections helps limit signal reflections.
Compare the specified characteristic impedance of the electrical assembly. The same value does not apply to an optical S/PDIF fibre, and an RCA connector shape alone does not establish the cable’s transmission-line design.
Characteristic Impedance — BNC Cable
For a BNC cable, characteristic impedance must match the intended interface; BNC assemblies can serve different impedance systems. Connector and cable sections both belong to the path.
Compare the complete cable rating with the equipment requirements. A 75-ohm label is not a resistance-to-ground reading, and physical connector compatibility alone does not establish matching.
Characteristic Impedance — SFP USB Cable
For an optical USB assembly, a characteristic-impedance claim applies to its specified electrical signal section, not to the light-carrying fibre. The relevant pair or interface must be identified.
Compare the stated differential or other measurement basis with the intended electrical path. Do not apply a coaxial cable’s impedance value to a USB data pair or infer complete link performance from this one property.