EXFO FTB-7000 OTDR for FTB-200 v2 - Manual (Page 327)

Description of Event Types
OTDR 313
Reflective Event (Possible Echo)
Reflective Event (Possible Echo)
This symbol indicates a reflective event that can be a real reflection or an
echo produced by another stronger reflection located closer to the source.
³
In the example above, the launched pulse hits the third connector, is
reflected back to the OTDR and reflected again into the fiber. It then
reaches the third connector a second time and is reflected once more
to the OTDR.
The application would therefore detect a reflective event located at
twice the distance of the third connector. Since this event is almost null
(no loss), and since its distance is a multiple of the third connector
distance, The application would interpret it as a possible echo.
³
A reflectance value is specified for reflective events (possible echo).
Reflected power
(dB)
Distance
(km)
OTDR connector
Second connector
Third connector
Reflective event (possible echo)