Television is certainly one of the most influential forces of our time. Through the device called a television set or TV , you are able to receive news, sports, entertainment, information and commercials. The average American spends between two and five hours a day glued to "the tube"! Have you ever wondered about the technology that makes television possible?
How is it that dozens or hundreds of channels of full-motion video arrive at your house, in many cases for free? How does your television decode the signals to produce the picture? How will the new digital television signals change things? If you have ever wondered about your television or, for that matter, about your computer monitor , then read on!
In this article, we'll answer all of these questions and more. See the next page to get started. Let's start at the beginning with a quick note about your brain.
There are two amazing things about your brain that make television possible. By understanding these two facts, you gain a good bit of insight into why televisions are designed the way they are. The first principle is this: If you divide a still image into a collection of small colored dots, your brain will reassemble the dots into a meaningful image. This is no small feat, as any researcher who has tried to program a computer to understand images will tell you. The only way we can see that this is actually happening is to blow the dots up so big that our brains can no longer assemble them, like this:.
Most people, sitting right up close to their computer screens , cannot tell what this is a picture of -- the dots are too big for your brain to handle. If you stand 10 to 15 feet away from your monitor, however, your brain will be able to assemble the dots in the image and you will clearly see that it is the baby's face. By standing at a distance, the dots become small enough for your brain to integrate them into a recognizable image.
Both televisions and computer screens as well as newspaper and magazine photos rely on this fusion-of-small-colored-dots capability in the human brain to chop pictures up into thousands of individual elements. On a TV or computer screen, the dots are called pixels.
The resolution of your computer's screen might be x pixels, or maybe x pixels. The human brain's second amazing feature relating to television is this: If you divide a moving scene into a sequence of still pictures and show the still images in rapid succession , the brain will reassemble the still images into a single, moving scene. Take, for example, these four frames from the example video:.
Each one of these images is slightly different from the next. If you look carefully at the baby's left foot the foot that is visible , you will see that it is rising in these four frames. The toy also moves forward very slightly. By putting together 15 or more subtly different frames per second, the brain integrates them into a moving scene. Fifteen per second is about the minimum possible -- any fewer than that and it looks jerky. When you download and watch the MPEG file offered at the beginning of this section, you see both of these processes at work simultaneously.
Your brain is fusing the dots of each image together to form still images and then fusing the separate still images together into a moving scene. Without these two capabilities, TV as we know it would not be possible. A few TVs in use today rely on a device known as the cathode ray tube , or CRT , to display their images. LCDs and plasma displays are other common technologies. It is even possible to make a television screen out of thousands of ordinary watt light bulbs!
You may have seen something like this at an outdoor event like a football game. Let's start with the CRT, however. The terms anode and cathode are used in electronics as synonyms for positive and negative terminals. For example, you could refer to the positive terminal of a battery as the anode and the negative terminal as the cathode. In a cathode ray tube, the "cathode" is a heated filament not unlike the filament in a normal light bulb. The heated filament is in a vacuum created inside a glass "tube.
Electrons are negative. The anode is positive, so it attracts the electrons pouring off the cathode. In a TV's cathode ray tube, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode. This tight, high-speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube. This screen is coated with phosphor, which glows when struck by the beam.
There is a cathode and a pair or more of anodes. There is the phosphor-coated screen. Rather than exciting gases as plasma TVs do, however, the cells contain a set of red, blue, and green filters covered by a layer of liquid crystals sandwiched between two pieces of glass.
Depending on the display type, each cell is linked to either electrodes or thin film transistors TFT , which trigger the necessary cells to create the image.
A backlight — most often cold-cathode fluorescent lamp — lights up the screen so the image can be seen. While LCDs are very light and thin, they are subject to "dead" pixels, where one or more cells on the screen do not change. Viewing LCD screens from an angle can also lower the picture quality. They have slower response times than plasma or CRT televisions as well, so images can "ghost" or blur in movement.
More recent versions of the LCD television use light-emitting diodes LEDs as the light source rather than cold-cathode fluorescent lamps. Also, LEDs generally emit a brighter white light, making these screens especially vivid.
Michael is a longtime EasyTechJunkie contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism.
In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. Michael Anissimov. Both audio and video signals are electrical in nature and are transformed into radio waves which can then be picked up by receivers your TV set. A transmitter not only transmits one channels audio or video signal, but in most cases many different channels.
A receiver is usually integrated in your TV set and this receiver is able to grab radio waves the transmitted signal and process these radio waves back to audio and video electric signals that can now be played on your TV set. A display device is usually a TV set, but can also be just a monitor. The display device is able to receive electrical signals usually sent from the receiver and turn these electrical signals to a viewable image.
Most standard TV sets incorporate a cathode ray tube CRT , however new display devices can include LCD liquid crystal display and Plasma gas charged display display devices among others. While most sound devices are built into your TV set in the form of speakers. Audio signals are obviously needed to match up with the video being shown to the viewer. Many newer TV sets have outputs to send the TV sound to high quality speakers that reproduce sound much better.
Since audio signals can include surround sound technology, the TV set is able to send audio signals to the proper speakers located around your room. There are three major ways to receive television broadcasts. Broadcast TV is usually defined as TV signals which are transmitted from a terrestrial source, usually a transmission tower.
Most broadcast TV signals are free to anyone with a receiver to pick them up. They include traditional TV channels that broadcast standard TV signals on specific radio frequencies. Here is the breakdown:. The Reason for using these Bands is that these radio frequencies are great for carrying TV signals both audio and video signals. These bands provide high quality audio and video with reatively low interference.
These radio waves have a long range and can penetrate structures such as walls and building exteriors. Satellite TV uses a different form of transmission. Instead of transmitting signals from the ground, satellite TV transmits from satellites orbiting the earth. In order to produce television you need special TV cameras and microphones which capture the video and audio signals. Three basic colors — red, blue and green can be mixed together to produce any other color.
The TV signal is carried by wire to an antenna , which is often on a high mountain or building.
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