Blonder tongue AMM-806, Справочное руководство

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Digital Signal Analysis
Carrier suppression or leakage is a special type of interference
in which it’s frequency equals the carrier frequency in the RF
channel. Carrier leakage can be superimposed on the QAM signal
in the I/Q modulator. In the constellation diagram, carrier leakage
shows up as a shifting of the signal states corresponding to the
DC components of the I and Q components.
Additive Gaussian noise can disturb the digitally modulated signal
during analog transmission, for instance in the analog channel.
Additive superimposed noise normally has a constant power
density and a Gaussian amplitude distribution throughout the
bandwidth of a channel. If no other error is present at the same
time, the points representing the ideal signal status are expanded
to form circular “clouds”.
Constellation Diagram — 64 QAM signal with
Additive Noise (SNR = 30.0 dB)
(
Note:
This diagram may also be obtained for other types of interference so
that a distinction from noise-produced patterns cannot be made)