Television Basics

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1. Television

Television is a telecommunication system for broadcasting and receiving moving pictures and sound
over a distance. The term has come to refer to all the aspects of television from the television set to
the programming and transmission.

Elements of a television set:

The elements of a simple television system are:
1. An image source - this may be a camera for live pick-up of images or a flying spot scanner for
transmission of films
2. A sound source.
3. A transmitter, which modulates one or more television signals with both picture and sound
information for transmission.
4. A receiver (television) which recovers the picture and sound signals from the television
broadcast.
5. A display device, which turns the electrical signals into visible light.
6. A sound device, which turns electrical signals into sound waves to go along with the picture.

Resolution:

Pixel resolution is the amount of individual points known as pixels on a given screen. A typical
resolution of 800x600 means that the television display has 800 pixels across and 600 pixels on the
vertical axis. The higher the resolution on a specified display the sharper the image. Contrast ratio is a
measurement of the range between the brightest and darkest points on the screen. The higher the
contrast ratio, the better looking picture there is in terms of richness, deepness, and shadow detail.
The brightness of a picture measures how vibrant and impacting the colors are measured in cd / m2
equivalent to the amount of candles required to power the image.

Cathode-ray tube (CRT) televisions
Old-style, cathode-ray tube (CRT) TV sets take the incoming signal and break it into its separate
audio (sound) and video (picture) components. The audio part feeds into an audio circuit, which uses
a loudspeaker to recreate the original sound recorded in the TV studio. Meanwhile, the video signal is
sent to a separate circuit. This fires a beam of electrons (fast-moving, negatively charged particles
inside atoms) down a long cathode-ray tube. As the beam flies down the tube, electromagnets steer it
from side to side so it scans systematically back and forth across the screen, line by line, "painting"
the picture over and over again like a kind of invisible electronic paintbrush. The electron beam
moves so quickly that you don't see it building up the picture. It doesn't actually "paint" anything: it
makes bright spots of colored light as it hits different parts of the screen. That's because the screen is
coated with many tiny dots of chemicals called phosphors. As the electron beam hits the phosphor
dots, they make a tiny pinpoint of red, blue, or green light. By switching the electron beam on and off
as it scans past the red, blue, and green dots, the video circuit can build up an entire picture by
lighting up some spots and leaving others dark.

2. How a cathode-ray tube (CRT) TV works

1. An antenna (aerial) on your roof picks up radio waves from the transmitter. With satellite TV, the
signals come from a satellite dish mounted on your wall or roof. With cable TV, the signal comes
to you via an underground fiber-optic cable.
2. The incoming signal feeds into the antenna socket on the back of the TV.
3. The incoming signal is carrying picture and sound for more than one station (program). An
electronic circuit inside the TV selects only the station you want to watch and splits the signal for
this station into separate audio (sound) and video (picture) information, passing each to a separate
circuit for further processing.
4. The electron gun circuit splits the video part of the signal into separate red, blue, and green
signals to drive the three electron guns.
5. The circuit fires three electron guns (one red, one blue, and one green) down a cathode-ray tube,
like a fat glass bottle from which the air has been removed.
6. The electron beams pass through a ring of electromagnets. Electrons can be steered by magnets
because they have a negative electrical charge. The electromagnets steer the electron beams so
they sweep back and forth across the screen, line by line.
7. The electron beams pass through a grid of holes called masks, which direct them so they hit exact
places on the TV screen. Where the beams hit the phosphors (colored chemicals) on the screen,
they make red, blue, or green dots. Elsewhere, the screen remains dark. The pattern of red, blue,
and green dots builds up a colored picture very quickly.
8. The circuit fires three electron guns (one red, one blue, and one green) down a cathode-ray tube,
like a fat glass bottle from which the air has been removed.
9. The electron beams pass through a ring of electromagnets. Electrons can be steered by magnets
because they have a negative electrical charge. The electromagnets steer the electron beams so
they sweep back and forth across the screen, line by line.
10. The electron beams pass through a grid of holes called masks, which direct them so they hit exact
places on the TV screen. Where the beams hit the phosphors (colored chemicals) on the screen,
they make red, blue, or green dots. Elsewhere, the screen remains dark. The pattern of red, blue,
and green dots builds up a colored picture very quickly.
11. Meanwhile, audio (sound) information from the incoming signal passes to a separate audio
circuit.
12. The audio circuit drives the loudspeaker (or loudspeakers, since there are at least two in a stereo
TV) so they recreate the sound exactly in time with the moving picture.

3. Photo: An old-style cathode-ray tube television being tested and repaired. The yellow box at the front
is a meter that tests the current flowing through the TV's circuits. The opened-up TV is behind and
we're looking from the back to the front (so the screen is pointing away from us).
Flat Screen Televisions

More modern LCD (liquid-crystal display) televisions have millions of tiny picture elements called
pixels that can be switched on or off electronically to make a picture. Each pixel is made up of three
smaller red, green, and blue sub-pixels. These can be individually turned on and off by liquid
crystals—effectively microscopic light switches that turn the sub-pixels on or off by twisting or
untwisting. Since there is no cumbersome cathode-ray tube and phosphor screen, LCDs screens are
much more compact and energy efficient than older TV receivers.
A plasma screen is similar to an LCD, but each pixel is effectively a microscopic fluorescent lamp
glowing with plasma. Plasma is a very hot form of gas in which the atoms have blown apart to make
negatively charged electrons and positively charged ions (atoms minus their electrons). These move
about freely, producing a fuzzy glow of light whenever they collide. Plasma screens can be made
much bigger than ordinary cathode-ray tube televisions, but they are also much more expensive.
LCDs are significantly smaller and lighter in weight than CRTs, however, which makes them better
for small offices and similar settings. They also give less glare and consume much less power than
CRT monitors. LCDs also do not have flicker problems and can run quite well at lower refresh rates.