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QMultiFlex-400™ Installation and Operating Handbook
6.2.27.2 View->Graphs->Constellation; Rx Constellation Monitor
The Rx Constellation Monitor feature shown in Figure 6-59 allows the modem to be used
as an oscilloscope in X/Y mode to view the constellation.
The Rx Constellation Monitor can be used to check for correct modem operation including
checking for signal distortion and phase noise. The persistence mode is useful for showing
any long-term effects due to phase noise and interference. Excessive phase noise can
cause cycle skips, seen as unwanted rotations within the constellation.
Note that MER and EVM figures are available on the panel on the right-hand side. These
concepts are explained in the following information.
Modulation Error Ratio (MER) and Error Vector Magnitude (EVM)
MER and EVM (as displayed on the Rx Constellation Monitor) measure
how imperfect the received signal is in relation to an ideal signal as in
the following example.
Figure 6-59 Rx Constellation Monitor
6-75
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