What does impedance mean and how does it affect RG6 cables?

Answer 1

Impedance is similar to resistance, but with an extra property called reactance that only affects AC signals. A steady DC signal only "sees" the resistance of a circuit or a cable, while AC "sees" both the resistance and the reactance. The resistance plus the reactance equals the impedance. The reactance includes both capacitance (a tendency to store electrical energy) and inductance (a tencency to store magnetic energy). For cables like RG6, the DC resistance is very low, only an ohm or less per hundred feet, while the impedance is 75 ohms. The impedance value of the cable is determined by the outer diameter of the center conductor, the inner diameter of the outer conductor, and electrical properties of the material between the two (the dialectric). For practical purposes, the only thing that really matters is that the impedance of the cable needs to be the same as the impedance of any connectors or adapters and the signal source and destination (load) it is used with. When one of those elements has a different impedance, some of the signal tends to reflect back to the source instead of continuing to the destination. Coaxial cables are generally used when it is important to preserve as much signal as possible between the source and the destination, as in broadcasting, or to protect the signal from external interference. The outer conductor is generally grounded and blocks interference from reaching the inner conductor, which carries the signal.