 - 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.
| LAST UPDATED: |
06 Nov 2006
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