EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 54)

Customizing the Graph and Data Layout
46 PSO-200
Eye Diagrams
Error Vector Magnitude (EVM) Diagram
The quality of the transmitted signal can be established by looking at the
error vector, which compares the received signal with an ideal signal,
taking into account both phase and magnitude errors.
The error vector magnitude (EVM) value is computed in the data
measurement window (excluding measurements from transitions).
When a pattern exists, EVM values are relative to the “expected” reference
constellation point. In random mode (no pattern), EVM values are relative
to the nearest constellation point.
EVM values on the Y axis range from 0 % to 100 %. In some cases, the value
can even be above 100 %.
For details about EVM measurements and calculations, see Measurements
for Constellation Charts on page 252.
NRZ-QPSK data