System Noise - Incoherent Interference
Coherent interference
- CSO/CTB, spurs or ingress produce symbol clusters with a hole in the center so they appear as
"donuts". This can also be a result of laser clipping or sweep interference.
Coherent Interference
Phase noise
- Also known as Phase jitter in a QAM signal, it is caused by transponders in the transmission path or by the I/Q
modulator. Phase jitter is a statistical quantity that affects the I and Q path equally. Phase noise causes the symbol clusters to
appear as arcs, particularly those near the edges of the constellation. Phase noise can also result from faulty headend
up/down converters.
CX380C User Manual RevA00
Page 29 of 105