Black and White television

2. REQUIREMENTS AND
STANDARDS
BLACK AND WHITE
TRANSMISSION
BLACK AND WHITE
RECEPRION

3. TELEVISION FUNDAMENTALS

4. The TV set
The TV set is the central element of any audio/visual
setup. It allows us to watch programs received by antenna,
cable or satellite and movies via our VCR. We can also use
the TV as a monitor to play games on game computers and
CD-I players. The development of television system has
made a revolutionary change in the field of electronics.
Television has become the most popular, powerful, most
media for communication and entertainment. Tele-Vision
means “to see at a distance”. The word television is derived
from a combination of two words “Tele” – a Greek word
denoting “far” a “vision” is taken from the Latin word “see”.

5. Development of Color Television
Several system of color television have been
developed in the fist color system approved by the
Federal Communications Commission (FCC), a motor-
driven disc with segments in three primary colors –
red, blue, and green rotated behind the camera
lens, filtering the light from the subject so that
the colors could post through in succession. The
receiving unit of this system formed monochrome
(black and white) images through the usual cathode
– ray tube, but a color white, identical with that
affixed to the common and synchronized with it,
transformed the images book to their original

6. This method is said to be “field –
sequential” because the monochrome image is
“painted” first in one color, then another, and
finally in the third, in rapid enough succession so
that the individual colors are blended by the
retentive capacities of the eye, giving the
viewer the impression of a full colored image.
This system, developed by the Columbia
Broadcasting System (CBS), was established bin
1950as standard for the United States by the
FCC. However it was not “compatible” i.e. from
the same signal a good picture could not be
obtained on standard black and white sets, so it
found scant public acceptance.

7. Another system, a simultaneous compatible
system, was developed by the Radio Corporation of
America (RCA). In 1953 the FCC reversed its 1950
ruling and revised the standard for acceptable
color television system. The RCA system meet the
new standards (the CBS system did not) and was
well received by the public. This system based on an
“element – sequential” system. Light from the
subject is broken up into its three color
components, which are simultaneously scanned by
three pick ups. However, the signals corresponding
to the red, green, and blue portions of the scanned
elements are combined electronically so that the
required 4.1.MHz bandwidth can be used.

8. In the receiver the three color signals are
separated for display. The elements, or dots, on
the picture tube screen are each subdivided into
areas of red, green and blue phosphor. Beams from
the three electron guns, modulated by the three
color signals, scan the elements together in such a
way that the beam from the gun using a given color
signal strikes the phosphor of the same color.
Provision is made electronically for forming proper
gray tones in black – and white receivers. The FCC
allowed stereo audio for television in 1984.

9. A television system may be required to produce:
1. The shape of each object, or structural
content
2.The relative brightness of each object, or tonal
content
3.Motion, or kinematic content
4.Sound
5.Color, or chromatic content
6.Perspective, or stereoscopic content

10. Television System and Standard

11. 5 different Television System:
1.Federal Communication Commission (FCC)
system for monochrome.
2. NTSC ( National Television Standard
Committee)
3.System for color (American Standard)
4.CCIR (comite Consultatif International de
Radio)System for monochrome
5.PAL (Phase Alternation by Lire) system for
colour.
6.SECAM (Sequential Technique and Memory
Storage) system for colour.

12. Standard American system European System
Number of lines per frame 525 625
Number of frames per second 30 25
Field frequency, HZ 60 50
Line frequency, Hz 15750 15625
Channel width, MHz 6 7
Video bandwidth, MHz 4.2 5
Color subcarrier 3.58* 4.43*
Sound system FM FM
Maximum sound deviation, kHz 25 50
Intercarrier frequency, MHz 4.5 5.5

13. Apart from the difference, the two major
systems have the following standards in common.
1.Vestigial sideband amplitude modulation for
video, with most of the lower sideband removed.
This is done to save bandwidth.
2.Negative video modulation polarity. In both
systems, black corresponds to a higher
modulation percentage than white.

14. 3.2:1 interlace ratio. This is can be seen from
4.4:3 aspect ratio. This is the ratio of the

15. Channel Frequency band, Channel Frequency band, Channel Frequency band,
designation Mhz designation Mhz designation Mhz
2 54-60 30 566-572 57 728-734
3 60-66 31 572-578 58 734-740
4 67-72 32 578-584 59 740-746
5 7682 33 584-590 60 746-752
6 82-88 34 590-596 61 752-758
7 174-180 35 596-602 62 758-764
8 180-186 36 602-608 63 764-770
9 186-192 37 608-614 64 770-776
10 192-198 38 614-620 65 776-782
11 198-204 39 620-626 66 782-788
12 204-210 40 626-632 67 788-794
13 210-216 41 632-638 68 794-800
14 470-476 42 638-644 69 800-806
15 476-482 43 644-650 70 806-812
16 482-488 44 650-656 71 812-818
17 488-494 45 656-662 72 818-824
18 494-500 46 662-668 73 824-830
19 500-506 47 668-674 74 830-836
20 506-512 48 674-680 75 836-842
21 512-518 49 680-686 76 842-848
22 518-524 50 686-692 77 848-854
23 524-530 51 692-698 78 854-860
24 530-536 52 698-704 79 860-866
25 536-542 53 704-710 80 866-872
26 542-548 54 710-716 81 872-878
27 548-554 55 716-722 82 878-884
28 554-560 56 722-728 83 884-890
29 560-566

17. -END-

18. Crystal RF Power Combining
oscillator amplifier amplifier network
Camera tube
Video AM Sound
amplifier modulating transmitter
amplifier
microphone
Scanning and FM
Audio
synchronizing modulating
amplifier
circuits amplifier
Basic monochrome television (transmitter)

19. Picture tube
Common Video
Video
tuner IF amplifiers
detector
amplifier
Sound IF Sound Audio Scanning
amplifiers demodulator amplifiers and
synchronizin
loudspeaker g circuits
Basic monochrome television (receiver)

20. Black-and-White
Transmission

21. Simplified monochrome television transmitter block diagram
Combiner
Video Mixing
Video Video Video
RF power and
-tape and
amplifie modulating vestigial
preampl switching amplifier
rs amplifier sideband
O.B. ifier amplifier
filter
ŧ
video
Video
camera preampli RF
fier amplifiers Sound
monitor transmitter
Blanking H* and V+ Audio
amplifier adder deflection Crystal sources
amplifiers oscillator (microphone,
tape,O.B.ŧ
sound
inputs)
* horizontal
H*and V+
+ vertical
H* and V+ Sync
blanking scanning ŧ outside broadcast
generators
generators generators

22. Camera tubes

23. • The camera tube has a mosaic screen,
onto which the scene is focused through
the lens system of the television camera.
• It has an electron gun which forms a beam
which is accelerated toward this
photoelectric screen.
• The beam scans the screen, from left to
right and top to bottom, covering the
entire screen 30 times per second.

24. Electronic Scan
(Camera Pickup Tube)
Object Lens Target
Electron
Beam
Video Signal

25. Video stages
• The output of the camera is fed to a video
switcher which may also receive videotape or
outside broadcast video at other inputs.
• The function of the switching system is to
provide the many video controls required.
• It is at this point that mixing or switching of
the various inputs, such as fading in of one
signal and fading out of another , will takes
place.

26. • The output of this mixing and switching
amplifiers goes to more amplifiers, whose
function it is to raise the signal level until it is
sufficient for modulation.
• Vertical and horizontal blanking and
synchronizing pulses are required by receivers
to control their scanning processes.

27. • The final video amplifier is the power
amplifier which grid modulates the
output RF amplifier.
• Because certain amplitude levels in the
composite video signal must correspond
to specific percentage modulation this
amplifier uses clamping to establish the
precise values of various levels of the
signal which it receives.

28. RF and sound circuitry
• The sound transmitter is a frequency modulated
transmitter the only difference is that
maximum deviation is limited to 25kHz instead
of the 75 kHz limit for FM broadcast
transmitter.
• The RF aspects of the video transmitter must
be broadband , in view of the large bandwidth
of the transmitted video modulated signals.

29. • The output stage is followed by a vestigial
sideband filter .
• The output of the sound and picture transmitter
is fed to the antenna via a combining network.
• Although both the picture and sound
transmitters are connected to the antenna with
a minimum of loss, neither is connected to the
other.

30. SCANNING

31. A television picture is scanned in a
sequential series of horizontal lines.
Scanning is a technique that divides a
rectangular scene into individual
horizontal lines.

32. Scanning a Focused Image

33. • The beam in the camera or picture tube moves
at a constant velocity across the screen and,
when it reaches the end of the screen on the
right-hand side , it “whips back” to the left
hand edge of the screen and starts again.
• Meanwhile, it has descended down the screen
so that the next line traced out is somewhat
below the first one.
• The process continues until the bottom of the
screen is reached and “whips back” to the top
of the screen.

34. HORIZONTAL SCANNING
• The total time taken from the beginning of one line to
the instant when the next line begins to be scanned is
63.5μs.
• This time includes not only the scan of the picture but
also the rapid return, or retrace, from right to left.
• A period of 10.2μs is allocated to the retrace which is
16% of the time allocated to scanning one line. That is,
the retrace time is 0.16H, and the active time is
0.84H, where H=63.5μs.

35. • Blanking is a process in which it reduces the
scanning bean current to zero, from just
before the beginning of the retrace until just
after its end.
This consists in adding a pulse to the
video waveform, at the right time and for the
correct period, to ensure that the signal level
has been raise to that corresponding to black.

36. Horizontal scanning:
1. A
s
t
h
e
a
c
t
i
v
e
b
e
a
m

37. VERTICAL SCANNING
• Basically, vertical scanning is similar to horizontal
scanning except for the obvious difference in the
direction of movement and the fact that
everything happens much more slow which is 60
times per second.
• The field rate of 60 Hz is the vertical scanning
frequency.
• This is the rate at which the electron beam
completes its cycles of vertical motion, from top
to bottom and back to the top again.
• Therefore the time of one field is 1/60 seconds.

38. • The picture repetition rate is 30 frames per second.
• A frame consist of two fields: first (odd) field and
second (even) field.
• Every field contains 262 ½ lines or 525 lines in a
frame.
• Therefore the number of lines per second is:
262 ½ lines ÷ 1/60 seconds = 15750 lines /second
Or
(30 frames/second)(525 lines/frames) = 15750
lines /second

39. Interlaced scanning:
• Here all odd line are scanned first from top to bottom,
and the even lines are skipped.
• After this vertical scanning cycle a rapid vertical
retrace causes the electron scanning beam to return to
the top of the frame.
• Then all even lines that were omitted in the first
scanning are scanned from top to bottom.

40. 1. Starting at the upper left corner of the frame at point A. for
this line 1, the beam sweeps across the frame with uniform
velocity to cover all the picture elements in one horizontal line.
At the end of this trace, the beam retraces rapidly to the left
side of the frame, to begin scanning the next horizontal line.
2. After line a is scanned the beam is at the left side , ready to
scan line 3, omitting the second line. The electron beam scans all
the odd lines, then, finally reaching a position, such as point B,
at the bottom of the frame.
3. At time B the vertical retrace begins. Then the beam returns to
the top of the frame to begin the second, or even field. The
beam moves from point B up to C, traversing a whole number of
horizontal lines.

41. 4. Horizontal scanning of the second field begins with the beam at
point C. after scanning a half-line from point C, the beam scans
line 2 in the second field. Then the beam scans between the odd
lines----it scans the even lines that were omitted during the
scanning of the first field. All the even lines of the second field
are scanned down to point D.
5. The vertical retrace in the second field starts at point B. from
here, vertical flyback causes the beam to return to the top. The
beam finishes the second vertical retrace at A where the first
trace started because the number of vertical retrace lines id the
same in both fields.
6. And so when it reaches point a 2 fields were completed and is
ready to scan the third field.

42. Video signal analysis

43. •Three parts of a composite video
signal:
1. the camera signal corresponding to
the variations of light in he scene
2.The synchronizing pulses, or sync, to
synchronize the scanning.
3.The blanking pulses to make the
retraces invincible.

44. Blanking
•The composite video signal contained blanking
pulses to make the retrace lines invincible by
changing the signal amplitude to black when the
scanning circuits produce retraces.
•All picture information is cut off during
blanking time. Normally the retraces are
produced within the time of blanking.
•When the picture is blanked out, before the
vertical or horizontal retrace, a pulse of suitable
amplitude and duration is added to the video
voltage , at the correct instant of time.

45. Horizontal Blanking
• Front porch is a part of the blanking signal which is located before the
sync pulse which is 0.02H wide or 1.27 μs.
• Back porch is a part of the blanking signal which is located after the
sync pulse which is 0.06H wide or 3.81 μs.
• After the front porch of blanking , horizontal retrace can begin when
the sync pulse starts, the flyback (retrace) is definitely blanked out
because the sync level is blacker than black.
• After the retrace to the left edge blanking is still in effect , as a result,
the first part of trace at the left is blanked. After the blanked traced
time at the left edge, the blanking pulse is removed.
• The effect of the horizontal blanking is illustrated by the black bars at
the left and right sides of the picture.

46. Vertical Blanking
• The vertical blanking pulses change the video signal amplitude to
black , so that the scanning beam is blanked out during vertical
retraces.
• The width of the vertical blanking pulses is 0.05V to 0.08V. If we
take 8 percent as maximum and since V is 1/60 seconds. The
vertical blanking time is:
(0.08)(1/60 seconds) = 1333 μs
• When we divide the vertical blanking time by the total line
period:
1333 μs ÷ 63.5 μs = 21 lines
Therefore, 21 lines are blanked out in each field and 42 lines are
blanked out in one frame.

47. Synchronizing pulses in Vertical Blanking
• The sync pulses inserted in the composite video signal during the
wide vertical blanking pulse includes equalizing pulses, vertical
sync pulses and some horizontal sync pulses

48. • The last-four horizontal scanning lines at the bottom of the
raster are shown with the required horizontal blanking and
sync pulses.
• Immediately following the last visible line the video signal is
brought to black by the vertical blanking pulse in
preparation for vertical retrace.
• The vertical blanking period begins with a group of six
equalizing pulse, spaced at half-line intervals.
• Next is the serrated vertical sync pulse that actually
produces vertically flyback in the scanning circuits. The
serrations also occur half-line intervals. Therefore, the
complete vertical sync pulse is three line wide.

49. • Following the vertical sync is another group of six
equalizing pulses and a train of horizontal pulses.
• During the entire vertical blanking period, no
picture information is produced, because the signal
is blacker than black so that vertical retrace can be
blanked out.

50. • The serrated vertical sync pulse forces the
vertical deflection circuits to start the flyback.
However, the flyback generally does not begin
with the start of vertical sync because the sync
pulse must build up charge in a capacitor to
trigger the scanning.
• If we assume that a vertical flyback starts with
the leading edge of the third serration, then the
time of one line passes during vertical sync before
vertical flyback starts. Also, six equalizing pulses
equal to three lines occur before vertical sync.
Then 3 + 1 = 4 lines are blanked at the bottom of
the picture, just before vertical retrace starts.

51. • As the scanning beam retraces from bottom to top
of the raster, five complete horizontal lines are
produced. This vertical retrace can be completed
easily within the vertical blanking time.
With 4 lines blanked at the bottom before
flyback and 5 lines blanked during flyback, 12 lines
remain of the total 21 during vertical blanking.
These 12 lines are at the top of the raster at the
start of the vertical trace downward. Therefore in
the total of 2 fields, 8 lines are blanked at the
bottom and 24 lines at the top.

52. The scanning lines that are produced
during vertical trace, but made black by
vertical blanking, form black bars at the top
and bottom of the picture. The height of
the picture is slightly reduced with blanking.

53. A simple video waveform

63. The television bandwidth is 6 MHz. The sub-carrier for the
color is 3.58 MHz off the carrier for the monochrome
information. The sound carrier is 4.5 MHz off the carrier for
the monochrome information. There is a gap of 1.25 MHz on
the low end, and 0.25 MHz on the high end to avoid cross-talk
with other channels. Television has a maximum frequency
bandwidth of 6 MHz. This says that the highest resolution
signal is something like 1/6MHz or 166.7 nS. This is
consistent with a 330 element scan line with a 8.7 uS
blanking time.

64. The lower visual sideband extends only 1.25 MHz
below its carrier with the remainder filtered out, but the
upper sideband is transmitted in full. The audio carrier is 4.5
MHz above the picture carrier with FM sidebands as
created by its ±25-kHz deviation.
The lower sideband is mostly removed by filters that
occur near the transmitter output. While only one sideband
is necessary, it would be impossible to filter out the entire
lower sideband without affecting the amplitude and phase of
the lower frequencies of the upper sideband and the carrier.
Thus, part of the 6 MHz bandwidth is occupied by a
“vestige” of the lower sideband (about 0.75 MHz out of 4
MHz). It is therefore commonly referred to as vestigial-
sideband operation. It offers the added advantage that
carrier reinsertion at the receiver is not necessary as in SSB
since the carrier is not attenuated in vestigial-sideband
system.

65. -END-

66. Black-and-White
Reception

67. Picture
tube
Deflection
V
coils
4.5-MHz 4.5-MHz AF and
sound sound IF Sound (FM) power
takeoff takeoff detector amplifiers
loudspeaker
VHF and Picture Video
Video Video
UHF tuners (common) IF output
detector amplifier
amplifiers amplifier
AGC
stage
Sync Vertical Vertical Vertical
separator sync deflection output
sync
separator oscillator amplifier
V
Damper
AGC
diode
Horizontal Horizontal Horizontal
Horizontal
sync
sync deflection output High-voltage
AFC circuit
H
separator oscillator amplifier power supply
AGC
H+V
sync
antennas

68. UHF antenna
45.75 and
UHF RF tuned
VHF RF tuned circuits
700.75 MHz circuits
175.25MHz (45.75MHz) (609.25 MHz)
VHF RF amplifier UHF diode
mixer
degna G
Ganged
VHF mixer tuned circuits
175.25 MHz (45.75MHz) UHF L.O tuned
45.75 and circuits
266.75 MHz (655MHz)
(45.75 MHz)
VHF mixer
UHF local
Picyure 1st IF oscillator (L.O)
VHF L.O. tuned circuits amplifier 45.75
221MHz MHz
VHF local oscillator (L.O.)
IF out to 1st picture
IF amplifier, 45.75 MHz

69. Fundamentals
TV receivers use the superheterodyne
principle. In addition, however, there is
extensive pulse circuitry to ensure that the
demodulated video is displayed correctly. To
that extent the TV receiver is quite similar to a
radar receiver, but radar scan is generally
simpler, nor are sound and color normally
required for radar. It is also worth making the
general comment that TV receivers of current
manufacture are likely to be either solid-state
or hybrid.

70. COMMON, VIDEO
AND
SOUND CIRCUITRY

71. TUNER
VHF tuner
•Must cover the frequency range from 54 to
216MHz Band.
•Antenna most frequently used for reception is the
Yagi-uda.
•Often used a turret principle

72. UHF tuner
•Must cover the frequency range from 470 to 890 MHz Band.
•The antenna used is quiet likely to be a log-periodic, with the
one antenna covering the whole band.
•Active stages are a diode mixer and a bipolar or FET local
oscillator.
•Used coaxial transmission lines instead of coils, and they are
tuned by means of variable capacitors.
•Alternative means of UHF tuning consists of having varactor
diodes to which fixed DC increments are applied to change
capacitance, instead of variable capacitors. One of the
advantages of this arrangement is that it facilitates remote-
control channel changing.

73. Three things happen when the VHF tuner is set to
the UHF tuner position:
•The UHF local oscillator is enabled
•The VHF local oscillator is disabled
•The VHF tuner RF and mixer tuned circuits are
switched to 45.75MHz

74. Picture IF amplifiers
The picture IF amplifiers are almost invariably double-
tuned, because of the high percentage bandwidth required. As in
other receivers, the IF amplifiers provide the majority of the
sensivity and gain before demodulation, consequently, three or
four stages of amplification are normally used. The IF stages
provide amplification for the luminance, chrominance and sound
information.
IF a TV receiver is misaligned or purposely mistuned, the
sound carrier may correspond to a point higher on the IF response
curve. If this happens, the extra gain at this frequency will
counteract the subsequent 4.5MHz filtering, and some of the
sound signal will appear in the output of the video amplifiers. This
will result in the appearance of distracting horizontal sound bars
across the picture, moving in tune width sound frequency changes.

75. Video stages
It will be seen that the last picture IF amplifier
is followed by the video detector and two video
amplifiers, whose output drives the picture tube, at
various points in this sequence , signals are taken off
for sound IF, AGC and SYNC separation.
Two functions of transformer in the emitter of the
first video amplifier:
1.To provide the sound IF takeoff point
2.The sound IF transformer thus acts as a trap, to
attenuate 4.5MHz signals in the video output.
Preventing the appearance of the sound bars.

76. The video amplifiers of the TV receiver have
an overall frequency response. The second stage
drives the picture tube, adjusting the instantaneous
voltage between its cathode and grid in proportion to
the video voltage. This modulates the beam current
and results in the correct degree of whiteness
appearing at the correct point of the screen, which
in turn is determined by the deflection circuits. The
blanking pulses of the composite video signal drive
the picture tube beyond cutoff, correctly blanking
out the retraces. Although the sync pulses are still
present, their only effect is to drive the picture
tube even further beyond cutoff. This is quite
harness, so that the removal of the sync pulses from
the composite video signal is not warranted.

77. The contrast and brightness controls are
located in the circuitry of the output video amplifier.
The contrast control is in fact the direct video
equivalent of the volume control in a radio receiver.
When contrast is varied, the size of the output
voltage is adjusted, either directly or through a
variation in the gain of the video output sage. The
brightness control varies the grid- cathode DC bias
on the picture tube, compensating for the average
room brightness.

78. The sound section
The sound section of a television receiver is
identical to an FM receiver. Note that the ratio
detector is used for demodulation far more often
than not. Note further that the intercarrier
system for obtaining the FM sound information is
always used, although it is slightly modified in
color receivers.

79. SYNCHRONIZING CIRCUITS
The task of the synchronizing circuits in a
television received information, in such a way as
to ensure that the vertical and horizontal
oscillators in the receiver work at the correct
frequencies.
Three specific functions of this task:
1.Extraction of sync information from its
composite waveform
2.Provision of vertical sync pulses
3.Provision of horizontal sync pulse

80. Sync separation
The “clipper” portion of the circuit shows the normal
method of removing the sync information from the
composite waveform received. The clipper uses leak-type
bias and a low drain supply voltage to perform a function
that is rather similar to amplitude limiting.
It is seen from the waveforms that video voltage
has been applied to an amplifier biased beyond cutoff so
that only the tips of the sync pulses cause output current
to flow. It would not be practicable to use fixed bias for
the sync clipper, because of possible signal voltage variation
at the clipper input. If this happened, the fixed bias could
alternate between being too high to pass any sync, or so low
that blanking and even video voltages would be present in
the output for strong signals.

81. Horizontal sync separation
The output of the sync clipper is split, a
portion of it going to the combination of C3and R2.
A positive pulse is obtained for each sync pulse
leading edge, and a negative pulse for each trailing
edge. When the input sync waveform has constant
amplitude, no output results from the
differentiating circuit. The time constant of the
differentiating circuit is chosen to ensure that, by
the time a trailing edge arrives, the pulse due to
the leading edge has just about decayed.

82. Vertical Sync separation
The coupling capacitor Cc is taken to a
circuit consisting of C1, R1, and C2, which
should be recognized as a standard
integrating circuit. Its time constant is
made long compared with the duration of
horizontal pulses but not with respect to
the width of the vertical sync pulse.

83. ecessary to drive the electron beam horizontally across the face of the tube 15,750 times a second and at the same time, move down the screen relatively slowly
Vertical-Deflection Circuits
To develop a TV picture on the
screen it is necessary to drive the
electron beam horizontally across the
face of the tube 15,750 times a second
and at the same time, move down the
screen relatively slowly and then back up
rapidly 60 times a second.

84. The 2-MΩ rheostat in the triode grip circuit with
the 0.003-mμF capacitor determines the frequency of
oscillation and enables the oscillator to be synchronized
by the received vertical sync pulses to produce the
correct vertical sweep frequency. This is called THE
VERTICAL HOLD CONTROL.
For vertical centering of the picture on the
screen, a DC bias can be introduced into the yoke
coils by using a center.-tapped potentiometer.
Centering can also be accomplished mechanically
by positioning of the yoke coils.

85. Transistorized vertical-sweep circuits
may use a multivibrator or a blocking-type
oscillator that develops narrow pulses at the
sweep frequency. The pulses are amplified
by a driver stage, and the required saw
tooth waveform is develop by an RC circuit
at the input of the output amplifier stag. An
IC may be used for all this circuitry except
for the larger capacitors and the vertical-
linearity hold and height- control
potentiometers.

86. ecessary to drive the electron beam horizontally across the face of the tube 15,750 times a second and at the same time, move down the screen relatively slowly
Horizontal-Deflection Circuits
The horizontal deflection section of a TV
receiver has many functions. It generates a
15,750 Hz saw tooth current that sweeps the
beam across the screen.

87. The same AC that accomplishes the horizontal
sweep is also stepped up and rectified to produce the
required high aquadag voltages. A small portion of the
horizontal fly back voltage is used to key automatic
gain control (AGC) or automatic frequency control
(ATC) circuits into operation.
The multivibrator could be synchronized by
feeding a positive or negative pulse (from the sync
separator) to one of its grid circuits. However any
received static or noise pulses could upset the proper
synchronization and result in the tearing cut of
portions of the picture.

88. -END-