After a strong reflection, the OTDR receiver is briefly saturated, so any event close behind it merges into the first spike. The event dead zone is the minimum spacing at which two reflective events show as separate peaks, around 1 m on short pulses for good instruments. The related attenuation dead zone, often 3 to 8 m, is the distance before a following event's loss can be measured, and both grow with pulse width.
Those two connectors are a meter apart in the panel, inside the event dead zone at that pulse width, so drop to 5 ns.
Every OTDR has a dead zone at its own front panel connector, which is the whole reason a launch cable exists.
Also heard as
- EDZ
Related terms
OTDR
Optical Time Domain Reflectometer: a tester that maps a fiber's loss and events by timing light reflected back along it.
Launch cable
A long reference fiber placed between the OTDR and the cable under test so the first connector can be measured.
Reflectance
The fraction of light reflected by a single event such as a connector, in dB, where more negative is better.
Event
Any point on an OTDR trace where the signal departs from the smooth fiber slope, such as a splice, connector or break.