Tektronix TekRanger 2 TFS3031, Service Manual

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Performance Check – TekRanger (serial nos. below B052000)
TFS3031 TekRanger/TekRanger 2 Service Manual
3–5
when the waveform finally recovers to within 0.5 dB of backscatter following
the event.
Dead Zone (refl)
0.5 dB
0.5 dB
Attenuation dead zone should measure the recovery time of the OTDR due to the
reflective event, and ignore noise unrelated to the event. The attenuation dead
zone measurement attempts to ignore random noise and real fiber imperfections
that appear on the fiber backscatter waveform. The measurement should include
any noise or error resulting from the reflective event such as undershoot on the
waveform before the reflective event, nonlinearity, offset, and undershoot or ring
on the waveform after the reflective event. Random noise can be reduced by
increasing the number of averages used in the measurement. Fiber imperfections
due to splices, mode distribution changes, point defects, and dimensional
variations are sometimes easy to identify by changing the measurement pulse
width. A fiber imperfection will look similar and remain at the same distance
when the pulse width is changed.