Television & Streaming

A broadcast system for sending images and sounds by wire or over the air.

Television, more often called TV, is that busy, colorful rectangle that brings information and entertainment from all over the world right into your living room. Television is a system that transmits moving images and sounds from one place to another by way of electrical impulses. The word television comes from the Greek “tele” which means “distant,” and the Latin “vision” which means “sight.” So when we watch television we see something that is taking place, or has already taken place, at a distance.

The ability to see things happening far away, both in distance and in time, is something we often take for granted as a part of everyday life. TV is found in nearly all homes, schools, and even many restaurants. We can watch the World Cup or the Olympic Games live, even when they take place on the other side of the world. Many homes have more than one TV, and people are now able to connect televisions with their computers or their phones. But 100 years ago, there were no televisions at all.

Many people are credited with helping to invent the television. Scientists and inventors began experimenting with the idea of sending moving pictures through the air in the 1800’s. John Logie Baird, a pioneer of early television development, publicly demonstrated a mechanical television that used spinning disks in 1926. But the first person to demonstrate an all-electronic television was Philo T. Farnsworth. He had grown up on an Idaho farm, where he first imagined creating television by dividing a picture into rows or lines – much the way he created rows of soil while plowing fields on the farm. On September 7, 1927 in San Francisco, 21-year-old Philo Farnsworth transmitted an image of a single line using a vacuum tube. Learn more about Mr. Farnsworth and his achievements.

The first electronic television that Mr. Farnsworth had created was very primitive. Pictures were originally very small, often blurry, and difficult to see. The creation of new and better ways to send images has improved and changed many times since then. For a view of the early development of television, visit Television History.

As a new invention, television had great potential to show people news and sports events happening far from their homes. In the early days of American television, NBC (National Broadcasting Company) and CBS (Columbia Broadcasting System) were the two primary broadcasting companies. Both are still in operation today. By 1943 the American Broadcasting Company (ABC) also entered the television industry. In time, news and sports programming were joined by comedy, musical talent, game shows and dramas that had previously been a part of radio programming. Television sets were big, bulky, and often sat on the floor. All television programs were shown in black-and-white and filmed with a single camera. Each program was scheduled to be broadcast at a specific day and time. Networks only showed programs during certain hours of the day and closed down late at night.

In the 1940’s most people still listened only to the radio. During the 1950’s many Americans bought their first television set, but even then some families were unable to afford a television in their homes as it was considered a luxury item. By 1960, however, 85% of American households had a television set. Color television was available by the early 1960s, but because people could not watch in color from the black-and-white televisions they already owned, it took some time for color TV to become widespread. In 1969 PBS (Public Broadcasting System) was born. PBS still brings you programs like Science Trek, Sesame Street, Odd Squad, and Wild Kratts, along with many others. In the 1960s and 1970’s, most Americans viewed programs from the broadcast companies CBS, NBC, ABC and PBS. But people living in some parts of the country were unable to view television because they lived in areas where they could not get TV service. Cable television became the new way to get service to homes and businesses that had not had access before. Satellite television came along in the 1980s.

Today, we have access to hundreds of channels and thousands of programs available 24 hours a day. In addition, video games, movies, the internet, video-conferencing, remote classes, and much more can be seen on home TV screens. People can watch television on their phones, tablets, or computers, and TV shows can be “streamed” to watch whenever a viewer desires.

The basic requirements for television are a TV camera that turns pictures and sounds into an electrical signal, a transmitter that sends the signal, and a TV receiver that captures the signal and turns it back into picture and sound.

In order to understand television, we first need to understand radio waves. Radio waves are part of what is known as the electromagnetic spectrum. The electromagnetic spectrum includes all light waves -- those that can be seen (called visible light) and those that cannot be seen like x-rays, microwaves, and many others. To learn more about the electromagnetic spectrum, visit Science Trek's Light & Color site.

Radio waves are the longest waves of the electromagnetic spectrum. When you tune a radio to a specific radio station, you are zeroing in on a given wavelength. Your radio converts the waves to mechanical vibrations and you hear music or the announcer speaking. Radios receive waves for both FM and AM radio stations. A television receives radio waves that have a slightly different wavelength.

The broadcasting company or television station sends out a signal using these waves. This TV signal has all of the images, music, dialogue, and data necessary for you to watch the program you have chosen. Each channel you select runs at a slightly different specific wavelength that carries that channel's programs. When you choose a channel, all but the selected signal is tuned out.

A television signal can reach a home TV in several ways. If your television has an antenna, the antenna picks up the signal that is sent out from the broadcast company or the television station. This is sometimes known as broadcasting “over the air.” In the earlier days of TV, everyone had an antenna. Sometimes the antenna sat on top of the television. These antennas were often called “rabbit ears.” Antennas can also be mounted to the roof or hidden inside the attic. But in order for an antenna to work, the signal has to be in direct line from the source to your TV. If mountains, canyons, or the curve of the Earth get in the way, no TV signal will be received.

Cable companies get around this direct line problem by sending the signal directly to your television. Cable companies have their own antennas which they use to collect the signal, and it is sent to individual houses through underground wires.

Satellite television can transmit further distances because the signal is sent from the source to a satellite orbiting the Earth, and the satellite sends it back to Earth again. The signal is then gathered in by a special antenna known as a satellite dish. Early satellite dishes were huge and took up a large part of the user's backyard. Over time they have been made smaller. Today, a home satellite dish is a little bigger than a dinner plate and attaches to the side of the user’s house. Larger ones are still used for broadcasting companies and have other uses in science and business.

Satellites used for sending television signals are in what is known as a geostationary orbit. This means that while the satellite is orbiting the Earth, it is keeping speed with the turning of the Earth. This allows it to stay over a given spot above the surface. Signals can be beamed from one location upward to a satellite and almost instantly be redirected down to locations anywhere on the Earth. Today, much of what you see on TV is transmitted by satellite signal. Learn more at Science Trek’s Satellites site.

A television program begins with a video camera. The show is filmed or videotaped at the TV station or another location. When this is done, the result is a series of still pictures, each with a slight change in the action. When played back, our brains piece these images together to form movement. It is almost like an optical illusion. We actually see each single still image, but it seems to us as fluid movement because it happens so fast. In fact, to make people on the screen look like they are moving, the television has to show at least 24 pictures every second.

Sound is added to include dialogue, conversations, sound effects, and music. Sometimes the sound is part of the original videotape, like when the newscaster reads the news. But in movies, sound can be added in layers. There may be a conversation layer, and sound professionals add sounds like sirens and squealing tires. Special artists known as Foley artists create additional sounds like people walking, doors closing, and even special-effects sounds like aliens landing or laser guns being fired.

All of this video and sound is changed into an electric TV signal. The signal is sent out using a transmitter to generate the radio waves. Transmitters of varying sizes are used in all sorts of equipment, from remote control cars to garage door openers to tracking collars that monitor animals’ migration habits. Transmitters for broadcasting television are large tower-like equipment used by television stations and broadcast networks. They are often located on hilltops, tall buildings, or other high places. Sometimes mobile transmitters are attached to the top of a van or truck when reporters go out to the site of a news event. These look a lot like an oversized satellite dish on a van.

Since 2009, all United States-based programming has been transmitted using digital signals. A digital TV signal is still transmitted using radio waves, but the signal carries pictures and sound as a number code with 0’s and 1’s, like the information stored in a computer. A digital signal can carry more information than an analog signal can, creating a more reliable transmission with better pictures and sound.

Televisions have changed over time. Until the 1990’s, televisions used cathode ray tubes or CRTs. These TV sets are not used much anymore, but a few are still around. You can recognize them by their large, bulky box shape. The CRT sends the video signal, in the form of beams of particles called electrons, through a vacuum to the back side of the screen. The back side of the screen is coated in phosphor which glows when the beam of electrons strikes it. The beam is steered across the screen by electromagnets. They create magnetic fields which attract the beam across the screen in a series of rows-- similar to Philo Farnsworth's farming observation. The beam moves back and forth in what is known as a raster scan pattern. The intensity of the beam changes as it moves across the screen to create rows of dots. These dots are known as pixels. The images refresh 60 times per second, fast enough to appear as smooth motion to the human eye. The viewer’s brain translates these rows into recognizable images.

Special signals are sent by the broadcaster to tell the television when to move the beam back and forth across the screen, how intense to make the beam, and when to repeat this process. The TV also sends the audio signal to speakers, which reproduce the sound.

In color television, there are three beams of electrons which are attracted to dots of phosphor that glow red, green, or blue when struck by the electron beam. These dots, or pixels, are very small and are arranged in a grouping of the three colors, repeated over and over across the screen. The colors we see as we watch a television image are combinations of the three colors. Again, the viewer’s brain is able to translate the various combinations into an image. Magazine and newspaper images use the same concept. Each magazine picture is made up of tiny colored pixels. From a distance, the pixels are too small to see, so we see groups of pixels as whole objects. But if you look at the picture with a magnifying glass, you will be able to see tiny colored dots – pixels.

Flat-screen televisions, which most people use today, do not use CRT technology. Flat-screen TVs avoid the large tube in the back of the television, making it possible to hang TVs on the wall and to have much larger, thinner screens. There are several kinds of flat-screen technologies. Plasma televisions use thousands of tiny cells filled with xenon and neon gases that light up in red, green, and blue when pulses of electrical current pass through them. LCD (liquid crystal display) screens are also flat screens, but instead of using gases they have liquid crystals which turn individual red, blue, or green sub-pixels on or off as needed to produce an image. A newer type of television technology is known as OLED (organic light-emitting diodes), which uses millions of light-emitting pixels. The encoded signal tells the individual LEDs what color to show and how brightly to glow, and all those tiny LEDs, or pixels, make up the picture. Learn more about different types of televisions.

As with all kinds of TVs, the light and sound waves emitted from the television are picked up by your eyes and ears, and your brain makes sense of what you hear and see.

A television program is not a simple thing to put together. It takes a large number of people to do all of the jobs necessary to bring programs to your television. And different kinds of programs need different people working on them. A news broadcast needs a different staff than a comedy show does. Here are just a few of the jobs that might be necessary to run a television program.

• Director: tells the actors where to stand and when to move

• Actor: acts out the story as written in the script

• Camera operator: videotapes the action

• Sound engineer: makes sure the sound quality is good.

• Set designer: organizes backgrounds such as furniture, walls, windows

• Lighting technician: makes sure the lights shine in the right places

• Costume designer: provides the clothing needed for each scene

• Makeup artist: turns the actors into the show’s characters (you know that actor isn't really a monster, but he sure looks like one!)

• Animal handler: takes care of any animals in the program

• Prop master: makes sure that all necessary items are there, such as pens, phones, books, mail, dishes, lightsabers, etc.

There as other jobs as well. Special effects people make the giant robot work and the rockets take off. People are needed to prepare film locations, feed the crew, and provide school for the child actors. Language experts teach actors to talk with accents, and special advisors might teach dance moves or sports positions. It takes a lot of teamwork to get a show to your TV screen! Next time you watch a movie or TV program, don't turn it off after the last scene.

Watch the credits at the end to get a better idea of how many people were involved in making the final product you just watched. Newscasts, game shows, sports programs, reality shows, movies and even Science Trek all have credits at the end to tell you who is responsible for getting that program to your TV.

Would you like to work in television someday? Learn more about careers in television production and broadcast engineering.

Another important person in the world of television is the consumer – that’s YOU! Television has the potential to be a window to the world, and to teach, inspire and entertain us. But as awesome as television is, it’s important to keep a healthy balance in your life. Too much screen time can interfere with outdoor exercise, sleep, reading, having fun with friends, and using your imagination. It’s important to be a smart consumer of television by choosing carefully the programs you watch. The world of television is one amazing part of the world you live in!