EXFO FTB -5240S/5240BP Optical Spectrum Analyzer for FTB 500 (NS-1434) - Manual (Page 347)

Managing Results
Optical Spectrum Analyzer 339
Managing Drift Test Results
In-Band narrow filter (InB nf): The In-Band narrow filter method
uses the In-Band method with additional processing to provide an
accurate OSNR value for the narrow carved noise. This is because with
narrow filters, the noise level under the peak is not uniform and the
OSNR value depends on the processing width selected.
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Peak detection level: indicates the minimum power level from where
the peak can be considered as a signal.
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RBW for OSNR: indicates the resolution bandwidth for the selected
OSNR value.
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Wavelength offset: indicates the offset value applied on the
wavelength.
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Power offset: indicates the offset value applied on the power.