EXFO MAX-700 - Manual (Page 368)

Description of Event Types
356 MAX-700
Echo
Echo
This symbol indicates that a reflective event has been detected after the
end of the fiber.

In the example above, the launched pulse travels up to the end
connector and is reflected back toward the OTDR. Then, it reaches the
second connector and is reflected again toward the end connector. It is
then reflected back to the OTDR.

The application interprets this new reflection as an echo because of its
characteristics (reflectance and particular position with respect to
other reflections).

The distance between the second connector reflection and the end
connector reflection is equal to the distance between the end
connector reflection and the echo.

There is no loss specified for echo events.
Reflected power
(dB)
Distance
(km)
OTDR connector
Second connector
End connector
Echo
Lightwave travel