HP 8591C, Руководство пользователя, Страница: 269 / 373

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Composite Second Order (CSO) Test Description
Three methods of measuring CSO are described here:
l
channel CSO
CSO using gating function
system CSO
The analyzer measures the total cable TV system power and adjusts its input
attenuation for optimum performance (refer to the graphs in Chapter 9).
Distortion near noise corrections are used to more accurately measure
distortion products less than 10
above the analyzer noise.
1. Channel CSD
The composite second order (CSO) test measures the relative level of second
order inter-modulation products that are offset from the carrier under test by
or +/-1.25 MHz.
The CSO beat at 1.25 MHz falls on the lower channel boundary and can be
measured without turning the channel off. This beat only appears on lower
channel numbers.
The trace is a time averaged display appropriate for measuring beats. The
marker does a local peak search to assure it is measuring the peak of the
beat.
2. CSD using
function
With the Option 107 installed, the carrier modulation does not have to be
turned off. After initiating the
test and after the gate function
has been selected with the GATE ON OFF key, a quiet line (horizontal line
without modulation) is selected. The CONTINUE is then pressed to
perform the measurement. The analyzer displays the in-channel noise and
CSO beats measured only during the quiet line. In this way, measurements
can be made without interrupting service.
A special case occurs for channels 5 and 6 in a standard channel plan. These
channels are placed 4 MHz above where they would be if they followed the
normal placement (as in IRC). This allows for measurement of CTB on these
channels with the gating function.
Refer to “Composite Second Order/Composite Triple Beat Test” in Chapter 2.
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