Promax 25 Mode D'emploi page 80

64 QAM set decoders require better than 23 dB MER to operate. To allow for
system degradation, a margin of at least 3 or 4 dB is preferred. However, QAM 256 set
decoders require better than 28 dB MER to operate with margins of 3 dB at least.
Typically the maximum MER displayed on portable analysers is about 34 dB.
MER was chosen as the preferred measurement for cable TV because of it's
similar to the analogue Carrier/Noise (C/N) measurement expressed in dB that most
people from cable industry are familiar with.
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Figure 23.- Modulation error ratio (MER)
USER'S MANUAL. PROMAX-25
RMS Error Magnitude
Ideal Symbol
Average Symbol Magnitude
09/2004