The
OTDR dead zone is the region of the trace nearest the
instrument. It is caused by the powerful OTDR test pulse
being reflected from the OTDR connection and crosstalk
in the OTDR splitter. It is characterized by a large
pulse that takes some time to recover and may even
undershoot the fiber trace. OTDRs need to use a launch
cable to allow the OTDR trace to settle down before
making any measurements.
