As a signal propagates down a length of cable, it loses some of its energy. So, a signal that starts out with a certain input voltage will arrive at the load with a reduced voltage level. The amount of signal loss is known as attenuation, which is measured in decibels, or dB. If the voltage drops too much, the signal may no longer be useful. All other values are suggested limits, not standards. In addition, the table shows limits for certain frequencies, although different frequencies can operate on each category of cabling.
Attenuation has a direct relationship with frequency and cable length.
The higher the frequency used by the network, the greater the attenuation. Also, the longer the cable, the more energy a signal loses by the time it reaches the load. A signal loses energy during its travel because of electrical properties at work in the cable. For example, every conductor offers some resistance to a current. Resistance, which is measured in ohms, acts as a drag on the signal, restricting the flow of electrons through the circuit and causing some of the signal to be absorbed by the cable.