The control amplifier combines the video, sync,
and blanking signals, all in proper sequence, into a
single continuous output to the amplitude modulator.
nizing (sync) and blanking pulses. These pulses are
applied to the control amplifier and become a part of
the transmitted signal. Horizontal synchronization
makes the horizontal scanning at the receiver occur at
the same time as the horizontal scanning at the camera.
Vertical synchronization makes the vertical scanning
at the receiver keep in step with the vertical scanning
Figure 8-4.--CCTV simplified block diagram.
at the camera.
Sync and blanking signals are also fed to the
The camera tube provides a means of converting
camera circuits, which develop the necessary control
light, from an object on which the camera is focused,
signals for the electron gun and the sweep voltages for
into electrical impulses. Light from the object is
the deflection coils (both horizontal and vertical).
focused on the light-sensitive surface (called the
In the carrier, the principal circuit is an oscillator
mosaic or photoconductive material) in the camera
designed to produce a steady, continuous RF signal.
tube by the lens system. The camera tube contains an
Its frequency is fixed and designated by appropriate
electron gun, which generates and controls a stream of
civil authority for the TV station in which it is used.
electrons. The gun directs the narrow stream of
In the amplitude modulator, the carrier signal is
electrons in such a manner that it traverses (scans) the
modulated by the video, sync, and blanking pulses.
mosaic line by line. As the beam strikes a spot in the
The composite (total) signal is then amplified by the
mosaic, it generates a small electrical impulse that
R amplifier and fed to the antenna for radiation into
corresponds to the lightness or darkness of that
particular tiny portion of the image. The electrical
impulses generated in this manner are sent to the video
The sound portion of the television signal is
amplifier (fig. 8-3).
transmitted by a frequency modulated R carrier. The
sounds are picked up by a microphone, amplified by
the audio amplifier, and fed to the frequency
modulator section. The sound earner frequency is
The control unit, as the name implies, is the
varied according to the frequency of the audio signal
being picked up by the microphone. The frequency
heart of the system. This unit connects all the other
modulated signal is then amplified by an R power
units of the system together. Drive pulses are
generated, and they develop the sweep and blanking
into space, or into a cable system installed throughout
signals required by the camera. Synchronizing and
blanking pulses are supplied by the control unit to
Video signals from the camera are amplified and
distributed to the receiver/monitor. The output signals
The picture-producing unit is commonly referred
from the control unit contain vertical and horizontal
to as the receiver/monitor unit. The receiver and the
blanking, sync, and video signals. The control unit
monitor (fig. 8-4) differ basically only in the circuits
consists of the following sections, shown in figure 8-3:
contained in each unit. The media of transmission
video amplifier, control amplifier, carrier, amplitude
between the receiver and monitor units are different.
modulator, radio-frequency (RF) amplifier, sync
This difference requires the receiver to employ
generator, and the audio controls.
additional circuits. (The media employed for the
Video amplifiers are designed to amplify a wide
receiver is radio waves, while the media for the
range of frequencies. The weak electrical impulses
monitor is normally cables.) The standard TV receiver
from the camera tube are built up by the video
contains the same circuits as the monitor, and, in
amplifier and fed to a control amplifier.
addition, contains the antenna system, tuner, R