HP 54600 Series User's And Service Manual page 292

Using Option 005 Enhanced TV/Video Trigger (HP 54602B)
To window in on harmonic distortion using FFT
The FFT function then shows the harmonic content of the subcarrier in the
figure below. Had the time/division and delays controls not been used to
zoom in on the desired subcarrier, the entire video signal (with many
frequency components) would have appeared in the frequency domain
display. These frequency components would have obscured the color
subcarrier and its harmonics. This example illustrates a general technique of
using the time domain controls of the scope to select specific time intervals
for FFT analysis.
Figure 3-12
The FFT function shows that the harmonic content of the color busrt is more than 31 dB below the
subcarrier
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