Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances. The extent of attenuation is usually expressed in units called decibels (dBs).
If Ps is the signal power at the transmitting end (source) of a communications circuit and Pd is the signal power at the receiving end (destination), then Ps > Pd. The power attenuation Ap in decibels is given by the formula:
Ap = 10 log10(Ps/Pd)
Attenuation can also be expressed in terms of voltage. If Av is the voltage attenuation in decibels, Vs is the source signal voltage, and Vd is the destination signal voltage, then:
Av = 20 log10(Vs/Vd)
In conventional and fiber optic cables, attenuation is specified in terms of the number of decibels per foot, 1,000 feet, kilometer, or mile. The less the attenuation per unit distance, the more efficient the cable. When it is necessary to transmit signals over long distances via cable, one or more repeaters can be inserted along the length of the cable. The repeaters boost the signal strength to overcome attenuation. This greatly increases the maximum attainable range of communication.