Reference
3–6
1710J-Series Waveform Monitors
The horizontal blanking interval is easily observed with a television waveform
monitor. The horizontal sync pulse has a specific amplitude and shape, and it
starts at a specific time in relation to the left and right edges of the picture. The
left, falling edge of the horizontal sync pulse determines the lock and position of
the picture on the screen. The color synchronizing burst keeps the receiving
picture monitor’s color decoder in step so that the intended color values may be
reproduced. All of these blanking interval signals are standardized and many
transmission systems pass them through unmodified. Since they are known
signal elements, they are useful as an indicator of signal path performance.
The shape of the horizontal sync pulse indicates mid-frequency distortions. A
rounding or over-peaking of the corners can indicate short trailing smears or
ringing upon video signal transitions.
The amplitude (height) of the sync pulse (nominally 274 mV or 40 IRE units for
NTSC or 300 mV for PAL) is an indicator of system gain. You want the same
sync level (unity gain) through all sections of your signal path. Any notches in
the sync edges or sync tip could indicate signal reflections or ghosting caused by
improper cable termination or multiple over-the-air signal paths.
The size and shape of the color burst can tell you something about the color and
detail performance of your system. The color burst should be the same amplitude
as your sync pulse. The matching amplitude between the sync pulse and color
burst provides a two point frequency response check of your system, telling you
that the gain of your system is the same at a low and a high frequency.
If you have any doubt about how the horizontal blanking interval should look as
the composite signal progresses through your system, it does not have to be
perfect, but it should look the same as it does at the source at every point down
the line.
To determine lower frequency distortions such as AC power hum or poor low
frequency response you can look at your video signal at a slower rate. Set
1710J-Series Waveform Monitor to display two fields (2 FLD). With dc
restoration off or in the slow position you can see any power line interference
moving slowly right-to-left in the display. Poor low frequency response will
cause abnormal brightness changes and horizontal banding in the picture and is
an indication that maintenance may be required.
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