Cisco Cisco DOCSIS EuroDOCSIS Transponder for GainStar Nodes and Amplifiers Guide De Montage
Status Information
Individual
cells
Low CNR
and/or
Low MER
Individual cells of QAM
constellation contain a fuzzy
and diffused pattern.
Individual
cells
Coherent
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.
Individual
cells
Gaussian
Noise
Individual cells contain a
complete and fairly uniform
smear up to all decision
boundaries, and are usually
caused by improper system
setup, too many amplifiers in
a cascade, damaged/
overheated hardware, and/or
low power.
Entire QAM
constellation
Phase Noise QAM constellation consists of
smeared, concentric, circular
patterns.
Entire QAM
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).
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