Anybody who has spent hours before a television set watching digitally transmitted pictures would wish to know what technology lies behind the television transmission that keeps people glued before their TV sets.
A television (often abbreviated as TV or T.V.; sometimes called , telly or the tube in British English) is a widely used telecommunication system for broadcasting and receiving moving pictures and sound over distance.
The term may also be used to specifically refer to a television set, programming or television transmission.
The word is derived from mixed Latin and Greek roots, meaning “far sight”: Greek “tele”, far, and Latin vision, sight (from video, vis- to see).
The television set receives wireless electromagnetic waves and converts them into acoustic and light energy for viewing. It works on the principle of digitally transmitted satellite signals sent to the space station from which digital channels are read by earth stations and sent directly to a home-based-television set via a radio signal.
Elements of Broadcast Television
There are a several major parts that are required in order to receive television broadcasts at home. They include an image source, sound source, transmitter, receiver, display device and a sound device.
The image source is the program: a movie, TV show or news bulletin that does not include the sound. The image source is usually recorded using a camera or a flying spot scanner.
The sound source is the audio signal of the TV programming whether coming from a movie, TV show or news bulletin.
It comes in form of mono, stereo or digitally processed sound.
Through the transmitter, both audio and video signals are sent over the air waves.
Transmitters usually send more than one signal (TV channel) at a time.
A receiver (TV set) is able to receive the transmitted signals (TV programs) and converts radio waves of audio and video signals to be processed back into an image and sound.
A display device; either a TV set or monitor, has the technology to turn the electrical signals received into visible light. On a standard TV set, this includes the technology of a Cathode Ray Tube (CRT).
Sound devices are usually speakers either built into the TV set or detached. These turn electrical signals into sound waves to play audio along with the video images that are seen on the screen.
Broadcast Television Signals
These are video and sound signals that are transmitted over the air. They can be picked up by anyone using a television set that has a receiver and an antenna.
Antennas are used to grab as much signals as possible and sometimes amplify the signal.
All TV sets have the ability to pick specific channels. Each channel is transmitted on its own frequency which can be tuned and received by a TV set.
Television Transmission Bands
Television is transmitted on various bands or frequencies that vary by country. Bands in use are I to V with VHF and UHF signals. VHF (Very High Frequencies) are usually channels 2 to 13. UHF (Ultra High Frequencies) are channels 14 to 83.
Band II carries FM radio and is therefore able to carry an audio signal.
Frequency modulation (FM) is the encoding of a carrier wave by variation of its frequency in accordance with an input signal to produce sound only and not images.
A Normal TV signal is located on Bands III to V which usually requires a bandwidth to carry both audio and video signals. Each TV channel is allocated a band width of 6 MHz. Channels work within given parameters; Band III - Channels 2 to 6 (54 to 88 MHz), Band IV - Channels 7 to 13 (174-216 MHz) and Band V - Channels 14 to 83 (470 to 890 MHz).
Both VHF and UHF are great frequencies for carrying TV signals.
They have a long range and can penetrate structures such as walls.
The higher bands are much higher in frequency and behave like light waves instead of radio waves.
They are usually obstructed by structures and need a clear line of sight. Many satellite signals can use these frequencies, but do require special equipment.
The Heart and Soul of Your Television
At the centre of the standard television set is the Cathode Ray Tube (CRT). Cathode means a negative terminal the opposite of an “anode” which means positive terminal.
The cathode creates negative charged electrons in a stream.
These are compacted by a focusing anode terminal and an accelerating anode terminal, which causes the electron stream to be compacted into a tight beam travelling at a high speed.
The beam is then directed to the TV set at the opposite end of the tube.
The flat area is coated in a thin layer of phosphor, a substance that lights up when it is struck by the electron stream.
The inside of the picture tube is also given a thin coating of conductive material, ensuring that all those electrons have somewhere to go after they hit the phosphors.
Now, if this was all there was to your Cathode Ray Tube, all you would see when you turned the television on is the tiny little circle of light, much like that tiny light at the centre of old television sets when you turn them on or off.
The electron beam needs to cross every pixel of phosphor on the screen to show an effective picture, and it does this with the help of steering coils.
A steering coil is a series of copper wires wrapped around the Cathode Ray Tube to make an electromagnet.
These electromagnets can create two separate electromagnetic fields within the Cathode Ray Tube, one vertical and the other horizontal.
TVs create images by creating small pixels or dots on the screen. Thousands of glowing dots on a screen in a certain pattern create a picture.
These dots are called pixels and the more pixels on the screen, generally the higher the resolution and better the image quality.
While a black and white TV has one beam, colour TVs have three beams; red, blue and green.
Colour TVs also have one screen on which you view the image, but behind this screen are three sheets of phosphor of red, blue and green colours. Black and white TVs only have one sheet of phosphor.
The colour TV creates colours by mixing both the three types of colour beams (red, blue, and green beams) and the three types of colour sheets (red, blue and green sheets).
An antenna is usually required to receive TV broadcast signals. Antennas are usually composed of materials that can capture radio frequencies (usually metal).
They are normally planted on top of a high structure and are generally light weight from 1 to 20ft or more.
Besides external antennas, there are plenty of antennas that are made for indoor use.
These are smaller in size and weigh less.
They may also include amplifiers to make the TV broadcast signal stronger. All antennas are attached to your receiver to give your TV set the best possible signal and ultimately the best picture possible.