Overview
As cable networks transition from the
carriage of analog TV signals to digital
signals, the second- and third-order nonlinear
distortion products, known as composite
second order (CSO) and composite triple beat
(CTB), are still present but now appear on
conventional spectrum analyzers to be similar
to random noise. Thus, to technicians the
distortion energy is indistinguishable from
random noise. A new digital signal processing
(DSP) technique has been developed to
process the spectral “noise” in a vacant band
to determine if the energy is random, or
correlated to a full-band nonlinear distortion
signal that could have created it. This paper
discusses the processing details of the new
test method and presents lab, cascade, and
field test results. These data demonstrate the
operational benefits of making nonlinear
distortion measurements in mostly- or alldigital
cable plants.
