Copper cables are good for signal transfer, but they are not perfect. Ideally, the signal at the end of a length of cable should be the same as at the beginning. Unfortunately, this will not be true in practice. All signals degrade when transmitted over a distance through any medium. This is because its amplitude decreases as the medium resists the flow of energy, and signals become distorted because the higher frequencies are attenuated more than the lower ones. Any transmission also consists of signal and noise components. Signal quality degrades for several reasons, including attenuation, crosstalk, and impedance mismatches. Attenuation Attenuation is the decrease in signal strength, measured in decibels (dB) per unit length. Attenuation occurs more quickly at higher frequencies and when the cable resistance is higher. In networking environments, repeaters are responsible for regenerating a signal before passing it on. Many devices such as hubs are, in fact, repeaters without explicitly saying so. Since attenuation is sensitive to frequency, some situations require the use of equalizers.
Factors affecting cable performance