Aeroflex ATB-7300, Руководство по эксплуатации, Страница: 57 / 92

Test Set Operation
Subject to Export Control, see Cover Page for details.
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2.4.5.H Constellation Tab
Provides a convenient way to repr esent various digital Phase-Shift Keying (PSK)
schemes. T he derived data variables of the sampled signal are displayed as a
collection of points, each having the value of one variable deter mining the position on
the horizontal axis and the value of the other variable determining the position on the
vertical axis at symbol sampling instants. The Constellation plot provides a visual
comparison of the two variables in the data set, to determine the relationship between
the two variables. It can be used to recognize the type of interference and distortion in
a signal. Error Vector Magnitude (EVM) is a vector in the I-Q plane between the ideal
constellation point and the actual point received.
Fig. 2-48 VHF Analyzer GUI Constellation Tab view
VDL Measurements win dow:
EV M (%) data field:
Displays the derived Error Vector Measurement as a percentage
I-Q I mb alance (%) d ata field :
Displays the level of imbalance between the derived I and Q points.
LO Leakage(%) data field:
Displays the derived offset of the symbol constellation from center.
Number of symbols data field:
Displays the derived number of symbol s repr esented in the demodulated data
packet stream of I-Q points.