EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 66)

Setting Up the Instrument in WDM Mode
60 FTB-5240S/S-P/BP
Setting Up WDM Analysis Parameters
4. Under Global analysis parameters, define the following parameters
as needed:

Peak detection level (dBm): indicates the minimum power level
from where the peak can be considered as a signal.

RBW for OSNR (nm): indicates the resolution bandwidth selected
for the OSNR calculation. This parameter is generally set to 0.1 nm
to allow for a common basis of comparison between different
OSAs having different effective resolutions. The instrument’s RBW
value is written below the graph. This parameter does not actually
have an effect on the acquisition, but is only a normalization factor
used to provide the OSNR value in a standardized manner.