Chapter 23 Television and Video Display Units 397
2. __________ is the point-to-point examination of a
picture.
3. One scan of 262 1/2 lines represents a(n)
__________.
4. What is a deflection yoke and what is its purpose?
5. The _________ triggers the oscillators in the receiver
and keeps them at exactly the same frequency.
6. What is a raster?
23.2 TELEVISION RECEIVERS
The television receiver is a fairly complex electronic
device. As you work through the block diagram of the
receiver shown in Figure 23-9, take note of the similari-
ties between your television set and the radio receivers
you just studied in Chapter 22.
Black-and-White Television Receiver
Figure 23-9 shows the parts of the television receiver.
This block diagram shows the links between the parts of
the television. Trace the signal path through the stages.
The purpose of each group of components will be appar-
ent. The name of each block reflects its purpose in the cir-
cuit. The following text takes you stage by stage through
a television receiver.
The RF amplifier serves a function similar to that in
the superheterodyne radio. The incoming television signal
is chosen by switching fixed inductors into the tuning cir-
cuit. These tuned circuits provide constant gain and selec-
tivity for each television channel. In this stage, the video
signal, with all its information, is amplified and fed to the
mixer.
In the mixer stage, the incoming video signal is
mixed with the signal from a local oscillator to produce an
intermediate frequency. The commonly used IF is 45.75
megahertz. When a channel is chosen with the channel
selector, the tuning circuit is changed. The frequency of
the oscillator is also changed so that it is always produc-
ing the IF of the correct frequency. A fine-tuning changes
the frequency of the oscillator slightly in order to provide
the best response.
The RF amp, mixer, and oscillator are combined in
one unit. The unit is called the tuner or front end of a tel-
evision. These units are usually put together in the factory.
Adjustments should not be made on these units unless you
have the correct instruments and thorough knowledge of
procedures.
The PIX-IF amplifiers amplify the output of the
mixer stage. This includes the 45.75 megahertz intermedi-
ate frequency, the video, and the aural information. To
provide maximum frequency response for each stage up to
45.75 MHz, each stage must amplify a broad band of fre-
quencies. The voltage gain of each stage is reduced. More
stages of IF amplification are required. In this system, the
Sound
IF amplifier
FM
detector
AF
amplifier
Video
amplifier
Video
detector
PIX-IF
amplifier
PIX-IF
amplifier
PIX-IF
amplifier
Mixer
RF
amplifier
Antenna
Local
oscillator
Sync
amplifier
DC
restoration
CRT
Speaker
Vertical
amplifier
60 Hz
Vertical
oscillator
Integration
network
Sync
separator
Horizontal
AFC
Horizontal
oscillator
Horizontal
output
High voltage
rectifier
Damper
Low voltage
power supply
Figure 23-9. Block diagram of a TV receiver.