From The Airwaves To Your Television
If you’ve ever watched television, you’ve probably wondered about the origins of the picture you were watching. Well, that television signal travelled a long way from the camera that recorded your favorite TV program to your television set. Let’s take a look at this trip through the airwaves to your TV.
The content has to be recorded by the camera and edited for television or broadcast live. Television cameras focus their lenses on the scene being filmed which are picked up by small, image-sensing microchips (either CCD or CMOS sensors), which convert the pattern of colors into digital, electrical signals. While older, traditional scanning cameras used 525 or 625 lines, the image sensing chips in today’s HDTV (High Definition) cameras have either 720 or 1080 lines for capturing more detail. Some cameras have a single image sensor capturing all colors at once; others have three separate ones, capturing separate red, blue, and green signals. Red, blue, and green are the primary colors from which any color on your TV can be made.
Broadcasting the Programs
The television station either transmits live footage or receives and transmits recorded footage. The footage has to be routed through a complex series of machines. Here at the Community Idea Stations, a PBS satellite receiver dish receives news and current event programming, as well as computer files that are stored on a computer server. The satellite signal is put through satellite receivers which have different channels within the signal, each channel houses a different program. Servers store the files from the satellite downlink and the files are file versions of programs for broadcast. Video and audio servers are essentially hard drives that store programs. The station's programming staff then creates a playlist for each channel. The Community Idea Stations broadcasts nine separate television channels including: WCVE, WHTJ, WVPT, WCVW, Create, Worldview, and PBS Kids. Before signals for the channels are broadcast, the signals for each channel come into an audio and video router for distribution. Then, the automation system picks the program to be broadcast and transmitted. The automation system is comprised of a collection of servers that determine which program airs when, based on the playlist created by the staff.
After the program is selected, the signal is sent to a transmitter where it is turned into electrical energy, and then sent to the TV broadcast antenna and out to the home viewer. The TV station also sends their signal to cable and satellite companies for distribution to the homes. The signal is sent digitally and is transmitted in a numerically coded form. The cable signal is either sent by a fiber-optic cable to your home and connected to your television, or if you have a satellite dish at home, the picture on the TV has been bounced into space to a satellite, and back down to your satellite dish and then into your house and to your TV.
(Photo: This is an ASI Encoder. WCVE has 4 program streams - 23.1, 23.2, 23.3 and 23.4. This encoder combines all of the streams to send to the TV transmitter for broadcast. The transmitter sends out that combined signal and then the TV receives the signal and breaks it back out to the 4 program streams for viewing.)
The Picture You See
Once the television set has the signal of the program being broadcast, the elements of the television LCD (liquid-crystal display) screen work together to produce a picture. LCD televisions contain millions of tiny picture elements called pixels that can be switched on or off electronically to produce a picture. Each pixel is made up of three smaller red, green, and blue sub-pixels. These pixels can be turned on and off by liquid crystals which are effectively microscopic light switches that turn the sub-pixels on and off by twisting and untwisting.
The Sound You Hear
In Digital Television, the picture and sound are transmitted together (multiplexed) and are synced up prior to reaching the TV Transmitter.
The Journey from Recording to Broadcast
As you can see it takes a lot of science, technology, and even math for you to be able to watch your favorite television program. From the technology behind the camera picking up the picture being recorded to the antenna transmitting the TV signal to your television set, watching TV is a complex process. Next time you sit down to watch your favorite television program you can envision all the science behind making that picture on your TV set appear like magic.
For more information about Television Broadcasts:
- YouTube: How a TV Works in Slow Motion - The Slow Mo Guys
- Explain that Stuff/Television
- Electronics: How Stuff Works
- Tech-Faq: How a Flat Screen TV Works
Article by Jordan Joseph, Science Matters Intern