Fiber
Optic MiniCourse: Reading An OTDR Trace
dB Scale
The
dB scale shows the attenuation of the OTDR signal as it
travels down the fiber under test, is scattered and the
scattered power is returned to the OTDR. It is used to
calculate the attenuation coefficient of the fiber
segments (when used with the distance scale) and joint
loss (splices and connections) in the cable under test,
It also shows the extra power returned from reflective
events that can be used to measure connection
reflectance.
Trivia: Since the signal travels down the fiber and
back, it is attenuated twice - once in each direction -
so the OTDR scales the reading to indicate the one-way
attenuation.
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