OptoTest OP940-SW Instruction Manual page 47

Troubleshooting (cont.)
Problem Possible Cause
Large reflections
in front of the
connection under test
Return Loss
measures Dirt and damage
80.1dB (SM)
or 58.1dB
(MM)
Connector measures
above the limitations
of the unit
Solution
If there is a reflection of magnitude 60dB or greater
within 2-4 meters of the connection under test,
the unit could potentially be unable to accurately
determine the magnitude of the reflection. Clean
the interfaces and if that doesn't improve the result,
try increasing the length of the reference cable
by 3-5 meters. If the issue persists it might be a
damaged front panel connector, in which case it will
need to be repolished or replaced.
Inspect all endfaces including any SAVer cables and
the front panel connector on the instrument. Clean
or repolish any dirty or damaged connectors. For
more info, please consult Application Note AN-137.
In Scan mode, if a reflection is seen when the
connector is open, but no reflection is seen
once the DUT is connected, it is possible that
the DUT has a high quality polish that exceeds
the linearized range of the return loss meter. For
example, many APC matings will measure better
than 80dB for SM cables and 58dB for MM cables
when properly mated.
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