Transmission Impairments
TX
Media are not perfect
Imperfections
cause impairments in the signal through the medium
This
means that the signal at the beginning and the end of the medium are
not
the same
What
is sent is not what is received
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Attenuation
o Loss of Energy
o When
a signal travels
through a medium,
it looses some
of its energy
in
order
to overcome the resistance of the medium
o That is why wire carrying electric
signals get hot
o Some of the electrical energy in the
signal is converted to heat
o To
compensate for this
loss Amplifiers are
used to amplify
the signal to
heat
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Decibel (dB)
ƒ Measures
the relative strength
of the two
signals or a
signal at 2
different
points
ƒ dB is negative if a signal is attenuated
ƒ dB is positive if a signal is Amplified
Relative
strengths of two signals or a signal at two points
dB
= 10 log 10 (P 2/P 1)
P
2 and P 1 are signal powers
Negative
dB means attenuation
Positive
dB means amplification
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