Tektronix MTM400 Manual do Utilizador descarregar pdf (Página 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).

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Tektronix MTM400 Manual do Utilizador Página 156