Cisco Model GS7000 4-Port Node 1 GHz with 42 54 Split Guía De Instalación
RF Constellation Page
4037424 Rev A
65
Shape
Focus
Impairment
Description
Individual cells
Coherent
Interference
Interference
Individual cells of QAM
constellation contain diffused
hollow circles or
―doughnuts‖. This indicates
an interfering carrier and
shows the effect of not
allowing the carrier to ever
reach the proper point in the
target range.
constellation contain diffused
hollow circles or
―doughnuts‖. This indicates
an interfering carrier and
shows the effect of not
allowing the carrier to ever
reach the proper point in the
target range.
Individual cells
Gaussian Noise
Individual cells contain a
complete and fairly uniform
smear up to all decision
boundaries, and is usually
caused by improper system
setup, too many amplifiers in
a cascade, damaged/
overheated hardware, and/or
low power.
complete and fairly uniform
smear up to all decision
boundaries, and is usually
caused by improper system
setup, too many amplifiers in
a cascade, damaged/
overheated hardware, and/or
low power.
Entire QAM
constellation
constellation
Phase Noise
QAM constellation consists of
smeared, concentric, circular
patterns.
smeared, concentric, circular
patterns.
Entire QAM
constellation
constellation
Gain Compression
QAM constellation looks
uniformly square, but the
outside corners appear to be
―smashed‖ toward center of
grid (compression in the RF
plant).
uniformly square, but the
outside corners appear to be
―smashed‖ toward center of
grid (compression in the RF
plant).
Entire QAM
constellation
constellation
I-Q Imbalance in the
Modulator
Modulator
Overall appearance of QAM
constellation is rectangular
rather than the desired square
shape (square inequality).
constellation is rectangular
rather than the desired square
shape (square inequality).
Entire QAM
constellation
constellation
Quadrature
Distortion
Distortion
Overall appearance of QAM
constellation has a twisted or
skewed parallelogram shape.
constellation has a twisted or
skewed parallelogram shape.