black region. Beyond this region in amplitude is the blacker than black region, which is
allocated to the synchronizing pulses. The blanking level (pulse) is shown in Figure 16.3.
The maximum signal excursion of a composite video signal is 1.0 V. This 1.0 V is
a video/TV reference and is always taken as a peak-to-peak measurement. The 1.0 V
may be reached at maximum synchronizing voltage and is measured between synchro-
Of the 1.0-V peak, 0.25 V is allotted for the synchronizing pulses and 0.05 V for
the setup, leaving 0.7 V to transmit video information. Therefore the video signal varies
from 0.7 V for the white-through-gray tonal region to 0 V for black. The best way to
describe the actual video portion of a composite signal is to call it a succession of rapid
The synchronizing portion of a composite signal is exact and well defined. A TV/video
receiver has two separate scanning generators to control the position of the reproducing
spot. These generators are called the horizontal and vertical scanning generators. The
horizontal one moves the spot in the
X or horizontal direction, and the vertical in the
Y direction. Both generators control the position of the spot on the receiver and must,
in turn, be controlled from the camera (transmitter) synchronizing generator to keep the
receiver in step (synchronization).
The horizontal scanning generator in the video receiver is synchronized with the cam-
era synchronizing generator at the end of each scanning line by means of horizontal
synchronizing pulses. These are the synchronizing pulses shown in Figure 16.3, and they
have the same polarity as the blanking pulses.
When discussing synchronization and blanking, we often refer to certain time intervals.
These are described as follows:
The time at the horizontal blanking pulse, 25 in Figure 16.3, is called the horizontal
The interval 23 in Figure 16.3 is called the front porch.
The interval 45 is the back porch.
The intervals are important because they provide isolation for overshoots of video at
the end of scanning lines. Figure 16.4 illustrates the horizontal synchronizing pulses and
The vertical scanning generator in the video/TV receiver is synchronized with the cam-
era (transmitter) synchronizing generator at the end of each field by means of vertical
synchronizing pulses. The time interval between successive fields is called the vertical
Sync pulses and porches.