ADInstruments S7200 Operation Manual page 141

AD INSTRUMENTS S7200 TV Signal Analyzer Operation Manual
way to measure CCN accurately, is to perform an in-service "gated" measurement,
with the help of gating technology and quiet line insertion in the vertical blanking
interval of the video signal that are off the viewable screen. (usually below line
12), if you choose a higher VITS line, you may start encountering video modulation,
thus visible interference on the television picture... In the gated mode, the S7200
will first measure peak carrier level, then will trigger on the appropriate VITS line
# (preset for each channel to be set in the channel plan editor) to measure system
noise. Sometimes, VITS lines are already quiet enough when video signals are
delivered by the broadcaster, but some operators prefer to add VITS
deletion/insertion to remove any uncertainty of measurement. (and so not to
assume lower quality signals coming from the broadcaster) Many other types of
test signals may be inserted for gated mode testing, such as in-channel frequency
response, diff.gain, diff phase. A quiet line is absolutely required when one needs
to measure CCN, CSO, CTB, or cross-modulation. The S7200 offers triggering
technology that accurately locks on a specific VITS line and provides very accurate
measurement results.
Figure 6-13 Gated CCN Measurement – Frequency Domain Waveform
The parameter setup needed for gated measurements are: video carrier
frequency, noise bandwidth, TV signal standard, odd/even field & line number.
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