c. In normal video transmission, the horizontal and vertical synchronizing
pulses occur at the end of each scanning line and each field respectively.
The
front porch of the horizontal synchronizing pulse occurs at the right edge of the
picture, and the back porch occurs at the left edge.
The vertical blanking
interval occurs during vertical retrace.
This information contained in the
vertical blanking pulse occurs at the top and bottom of the viewing screen. Since
all of the synchronizing and blanking information occurs at the edges of the
picture area, its information is hidden by the picture tube mask.
d. Though detailed information may be difficult to distinguish, the general
shape of the vertical blanking interval can be observed on most standard receivers
and monitors by rotating the vertical-hold control until the vertical blanking bar
is located in the viewing area.
The horizontal synchronizing and blanking pulses
at the end of each scan line are much more difficult to observe.
With the
modifications normally provided, the standard television monitor eliminates any
definition, vertical displacement, or horizontal displacement problems. The pulse
cross display can be observed instantly or monitored continually for extended
periods of time.
e. The individual lines can be seen more readily if the horizontal and
vertical scanning process is expanded.
As a result, the pulse cross display
information is seen in more detail. Expansion of the picture tube sweep circuits
permits the horizontal and vertical synchronizing and blanking information to be
placed in the viewing area of the picture tube.
f. Interpretation of the pulse cross display is relatively easy when you
understand that the individual pulse amplitudes are indicated by light intensity.
In the pulse cross display shown in Figure 3-26 the horizontal dimensions of the
light intensities are relative measures of time or pulse widths. Use Figure 3-26
to identify the following pulse group patterns:
(1) The horizontal synchronizing pulse duration (0.075H-0.98H).
(2) The horizontal blanking pulse duration (0.165H-0.18H).
(3) The vertical synchronizing pulse interval (0.42H-0.44H).
(4) The vertical blanking interval (13.1H-21.0H).
(5) E and F- the equalizing pulse intervals.
(6) G- the six dark lines which show vertical synchronizing pulse duration.
(7) I- the equalizing pulse duration (0.5 horiz sync width).
(8) H- the horizontal blanking and synchronizing pulses that continue to
occur at the end of each horizontal video scan line until the beginning of the next
vertical blanking interval.
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