Ccn, C/Cso And C/Ctb Gated Measurement - ADInstruments S7200 Operation Manual

AD INSTRUMENTS S7200 TV Signal Analyzer Operation Manual

7.4.1. CCN, C/CSO and C/CTB Gated Measurement

CCN, C/CSO and C/CTB all can do gated measurement, but C/CTB gated
measurement is slightly different from C/N and C/CSO gated measurement
because the C/CTB interference falls right at the Video carrier frequency. First,
let's talk about CCN and C/CSO gated measurement.
CCN gated measurement needs to measure video signal carrier peak level and
corrected noise level (over a specified bandwidth) on a quiet line during the
vertical blanking interval, and then uses the two results to calculate CCN.
C/CSO gated measurement also needs to measure video signal carrier peak level
and second order beat on a quiet line during the vertical blanking interval, and
then uses two results to calculate C/CSO.
C/CTB gated measurement is definitely different from CCN and C/CSO
measurement, because the third order beat coherent distortion is located directly
at the video carrier frequency. By definition, this signal is covered by the video
carrier. If you want to measure the third order beat, you must shut off the video
signal carrier. In normal measurement method, you would need to shut off the
modulator, let the video carrier level disappear, and then measure the third order
beat right at the video carrier frequency. In gated measurement mode, it is
suggested that you use a quiet line inserter, which gate off at necessary time, (at
the specified field). The S7200 first measures the video carrier peak level during
the sync pulse, then, while the quiet line inserter removes a specified line at the
same time in every frame. The instrument uses the gated function to measure
third order beat during that specific quiet line period. The instrument uses two
results to calculate the C/CTB. The effects of removing a quite line during a specific
vertical blanking interval are the same as if you would shut off the modulator, but
at a very specific time, and for a very short time. Figure 7-14 below describes how
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