Transmission impairments
There is always a difference in received signal and
transmitted signal which is known as impairment in the signal. There are
several agents which may cause different kinds of impairments in these signals.
These impairments may be attenuation, distortion, and noise; depending on those
agents which cause these impairments.
Attenuation
Attenuation means loss in energy of the signal. When this
signal travels through a medium, it loses its energy against the resistance
offered by the medium. These resistances may be due to electrical heating of
wires –“if network is wired”. It is similar to damping of signals which we
study in 11 and 12 grade physics. To regain energy of a signal so that it may
not lose its energy completely before reaching destination, amplification of
the signal is done. Amplifiers are installed for this purpose.
Distortion
Distortion is considered as the change in form or shape of a
wave. A signal is generally a composite wave. This wave is made from many
simple sine waves of different frequencies. When these waves with different
frequencies travel from one rare medium to a dense one, or from one dense
medium to a rare there occurs different amount of delays between them. These
difference in component waves make them to combine in a composite signal which
is different in shape from transmitted signal.
Noise
A noise may be a thermal noise: due to random motion of
electrons in a wire carrying signal; induced noise: generated by motor
vehicles, traffic, home appliances etc.; crosstalk: it is noise created when
one nearby wire affects the wire carrying the signal; impulse noise: an impulse
noise is a signal with its one pulse containing a huge amount of energy, which
affects original signal. These may be due to lightning, or from power lines
etc.
