Fluke DTX-1800 Technical Reference Handbook page 197

Event
Hidden
The event is within the
attenuation deadzone of
the previous event.
Gainer
An apparent gain in the
strength of the returned
signal.
Table 7-3. Event Types (cont.)
The event is detected, but not enough information is available to measure its loss
separately from the previous event. Since the hidden event's loss can't be determined, it
is not shown.
The hidden event may be a connection, a sharp bend, or a crack within the deadzone of
the previous connection.
If the event is not a connection, inspect the fiber near the event's location. Use a visual
fault locator to reveal faults.
Caused by a connection between two fibers with different backscatter coefficients,
numerical apertures, core diameters, or mode field diameters.
A gainer can also occur when measuring loss across a very reflective connection.
Clean the connection. Check the fiber type on either side of the connection. Replace fiber
if necessary. Matching fibers may have different tolerances, which can cause gainers at a
connection. In these cases, the connection is good and does not require rework.
Tip: If the gainer is caused by different backscatter coefficients, and you test the fiber from
the other end, the gainer event will show a loss. Adding this loss to the event's gain
provides the true loss of the event.
Using the OTDR Module
Looking at OTDR Test Results
Possible Causes
7
-continued-
7-39