EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 128)

Setting Up the Instrument in Drift Mode
122 FTB-5240S/S-P/BP
Setting Up Drift Analysis Parameters
3. Select the Activate all thresholds option to manually set the channel
threshold values. If this option is not selected, all the thresholds will be
deactivated, results are displayed without a Pass/Fail status in the
Channel Graph, Channel History and Channel Results tabs.
4. Enter values in the boxes as explained below:

Wavelength/Frequency (nm/GHz): central wavelength/frequency
of the channel.

Signal power (dBm): signal power for the selected channel
(excludes noise).

OSNR (dB): Optical Signal to Noise Ratio, given by Signal power
(according to the current calculation method, in dBm) minus
Noise (according to the current calculation method, in dBm).
5. Press OK to save the changes and close the window, or press Cancel to
exit without saving.
Press Restore Defaults to remove all the changes and apply the default
values.