Atec Agilent-8591C - Manual (Page 6)

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C/N accuracy (single channel) ± 1 dB accuracy
CSO accuracy (with external preselector filter)
CTB accuracy (without external preselector filter) CTB accuracy (without external preselector filter)
C/N, CSO, and CTB measurements
The four graphs summarize the combined CaLan 8591C and 85721A
characteristics for C/N, CSO, and CTB testing on cable TV systems for
CSO and CTB measurements with up to 77 channels and no amplitude tilt,
and for C/N measurements with single channels. C/N, CSO, and CTB
measurement accuracies and ranges can be read from the relevant
graphs. They depend on the visual carrier peak level, the measurement
reading, and the total power input to the analyzer. For C/N measurements
with a preselector, there is no optimum range and the accuracy bound-
aries drop by the preselector’s insertion loss (typically 2 dB).