HP 54645A User's And Service Manual page 162

Making Measurements with HP 54645A/D Oscilloscopes
To analyze video waveforms
Triggering on both TV Fields at the Same Time
The HP 54645A/D Oscilloscopes can trigger on the vertical sync pulse in both TV
fields at the same time. This allows you to view noninterlaced video signals
which are common in today's computer monitors. To trigger on both sync
pulses, press Field 1 and Field 2 at the same time, or press Vertical (HP 54645A).
TV Trigger Operating Hints
The color burst never really changes phase, it just looks doubled triggered
because its frequency is an odd multiple of one half the line frequency.
When looking at live video (usually a field), use peak detect to improve the
appearance of the display.
When making cursor measurements, use Autostore since you are usually
looking for pulse flatness and extremes.
When using line trigger, use minimum holdoff to display all the lines. Due to the
relationship between the horizontal and vertical sync frequencies the display
looks like it is untriggered, but it is very useful for TV waveform analysis and
adjustment because all of the lines are displayed.
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