Tektronix MTM400 - Manual (Page 156)

Interface Configuration and Interpretation
3-112 MTM400 MPEG Transport Stream Monitor User Manual
Input Card Screen - QPSK (L-Band)
Figure 3-39: Input card screen - QPSK (L-Band))
The constellation display in the graphing area is a representation of the digitally
modulated carrier's instantaneous phase and amplitude for each transmitted
symbol. A good constellation will have well-defined dot clusters in tight
formations; each cluster should be centered in a grid overlay square. The overall
shape of the dot clusters should form a square as represented by the outer edges of
the grid.
The Grid area of the screen contains the following controls:
Size This selection will be dictated by the installed interface card. If
the Auto checkbox is selected, the grid size can be selected from
the drop-down list.
Clear Points Clears all points from the display grid.
The Readings area of the screen contains the following controls:
MER (dB) (Modulation Error Ratio) Provides a single 'figure of merit' for
received signal. It is the ratio of 'ideal signal vectors' to 'errored
signal vectors' expressed in dB. MER is similar to a
signal-to-noise measurement (ref: TR 101 290).