VeEX CX380C, Руководство пользователя

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Cliff Effect - Digital Carriers
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7.1.3 Constellation Measurements
In contrast to measuring techniques used on digital TV signals transmitted via satellite, a wider and necessary range of measuring
techniques is provided for broadband cable testing. The influence acting on the broadband cable signal, which can be modulated
with up to 256QAM, are more varied and critical than in the satellite domain.
Constellation measurements are an example of such advanced measurements and are an ideal tool to identify QAM modulator
problems.
QAM Power Level (numeric in dBmV/dBuV)
MER (numeric in dB) is an indication of the operating margin of the system
Pre BER & Pre Error Seconds (numeric) is the error rate of the incoming signal prior to being corrected FEC circuitry
Post BER & Post Error Seconds (numeric) is the error rate of the signal after the FEC has corrected all the possible errors
Severely Error Seconds (numeric)
Max Adjacent Channel Delta (numeric in dB)
Constellation (graphic)
Zooming in on Constellation
The constellation display supports a zoom function. For QAM64 and QAM256 modulation, the constellation is split into 4
quadrants for simplified viewing. Tap on any of the four quadrants to zoom into this selected quadrant.
CX380C User Manual RevA00 Page 26 of 105