noise can result from headend up/down converters or by the I/Q modulator.
IQ Imbalance is when the constellation is not symmetrical in shape (it is taller than it is wide) - this due to gain difference in
the I and Q channels which may be caused by bad baseband amplifiers, modulators or filters.
The constellation display supports a zoom function. For QAM64 tap on the graphic and the entire constellation is zoomed. For
QAM256 modulation, the constellation is split into 4 quadrants for simplified viewing. The user can tap on any of the four
quadrants, which will zoom this specific quadrant.
8.0 Tilt Measurement
Tilt measurement is used to check the channel levels at the lowest and highest frequencies because level variations across the
frequency spectrum are indicative of distortion. Tilt measurement is also the most efficient tool for balancing distribution amplifiers.
By tapping on the channel bars, the Tilt measurement will measure the two most recently selected channels.
Note:
Typically, the same analog and digital channels which have been recommended or defined for the
Scan function should be used when performing Tilt measurements. Often tilt measurements are useful to
identify excessive cable lengths at the customer premises that can cause high frequency roll off.
CX100/110/120/150/180 series e-Manual D07-00-002 Rev B01
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