OTDRs are often supplemented with visual fault locators, which emit a bright red laser light into the fiber. If the fault is close enough, the reflected light may be visible to the naked eye. An area of noise lies at the end of the trace and is mostly attributable to the receiver. Unfortunately, the better the dynamic range, the worse the deadzone and vice versa. If the OTDR emits a second light pulse before the previous one has left the fiber, the receiver will see the echoes from the two pulses simultaneously and create a false event.
Proper setup is needed to prevent false ghosts.
If there are two highly reflective connectors, light reflected by the more distant connector can be reflected back away from the OTDR by the closer connector. Ghosts will often appear at multiples of the length of the launch cable. Ghosts can be especially problematic in short cables, which have insufficient length to attenuate them. Splices or less reflective connectors are needed to eliminate real ghosts. Gainers Gainers are associated with points at which two different fibers are joined.