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# What is the algorithm used to calculate the 3-point OSNR in the WaveAnalyzer?

To determine the OSNR you need to calculate the powers at the 3-point OSNR locations (P_{signal}, P_{left}, P_{right}).

1) Take a scan using the lineardata command with 150 MHz resolution. It’s important to retrieve the data in units of mW rather than dBm using this command:

http://<ip>/wanl/lineardata/text

2) Select two noise windows of 12.5 GHz width on either side of the signal. Integrate to find the total power within each to give you P_{left} and P_{right.}

3) Select a 12.5 GHz window centered on the signal. Integrate to find P_{signal}, the signal power.

4) Calculate the OSNR ratio using the following formula.

5) Convert the ratio to dB using the following equation:

An explanation on how to integrate the power within a specific frequency window is given in this article:

How to do I integrate power over a specific frequency window?