How does Television Broadcasting work?

While millions of people watch television each day, many of us aren't quite sure how the technology works. Television has been around for many decades and although some of the technology components have changed over the years, the way in which television broadcasts work is still pretty much the same.

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, a sound source, a transmitter, a receiver, a display device and a sound device.

Image Source

The image source can be defined as the program. It can be a movie, TV show, news program, etc. The image source is just the video of the source and does not include the sound. Usually the image source has been recorded on camera or flying spot scanner.

Sound Source

We already have the image source, let's say the video of a movie, now to complete the media, we also need the sound. The sound source is the audio signal of the TV programming whether coming from a movie, TV show, news program, etc. It can come in the form of mono, stereo or even digitally processed surround sound.

Transmitter

A transmitter is what sends both audio and video signals over the air waves. Transmitters usually transmit more than one signal (TV channel) at a time. A transmitter modulates both picture and sound into one signal and then send this transmission over a wide range to be received by a receiver (TV set).

Receiver

A receiver (TV set) is able to receive the transmitted signals (TV programs) and turn radio waves which include audio and video signals into useful signals that can be processed back into an image and sound.

Display Device

This is either a TV set or monitor. A display device has the technology to turn the electrical signals received into visible light. On a standard TV set this includes the technology CRT (Cathode Ray Tube).

Sound Device

The sound device are usually speakers either built into the TV set or that accompany the TV set that turns electrical signals into sound waves to play audio along with the video images that the person is viewing.

Broadcast Television Signals

Broadcast Television Signals are video and sound signals that are transmitted over the air. They are usually free to be picked up by anyone using a television set that has a receiver and an antenna. Antennas are used to grab as much signal as possible and to sometimes amplify the signal.

All TV sets include the ability to switch the receiver's tuner to pick up specific channels of programming. Each channel is transmitted on its own frequency which can be tuned in and received by your TV set.

Broadcast TV vs. Satellite TV and Cable TV

There are three main ways to receive TV programming, one is through broadcast television, and the other two are through satellite TV and cable TV.

Broadcast TV

Broadcast TV are audio and video signals transmitted over the air waves from a ground based transmitter. These signals are usually free to pick up and are on specific frequency spectrums.

Satellite TV

Satellite TV is usually a digital TV signal broadcasted from a satellite flying in space, orbiting the earth. They are usually pay services that require special equipment to receive programming and operate on special frequencies.

Cable TV

Cable TV are pay TV services that send out signals not over the air, but through cable that runs from the cable company to the viewers home. There are many types of cables used from copper cable to fiber optic cable. The signal can be analog or digital.

Television Transmission Bands

Television is transmitted on various bands or frequencies. Transmission bands vary by country. In America, the bands III to V are used, they include VHF and UHF signals.

Band I

It is important to note that lower band signals such as bands I do not have enough bandwidth, which means they can't carry lots of information or data..

Band II

Band II in America is what carries FM radio. While this band is able to carry an audio signal, adding video to the signal would overcrowd it and it would be inferior to the signal that you receive today.

Bands III , IV and V

A Normal TV signal is located on either Band III, IV or V. Usually these bands require bandwidth to carry both audio and video signals. Most TV signals have about 4MHz of bandwidth for the video portion, when you add on the sound portion of the signal the signal will have a total of about 6 MHz. The FCC has allocated each TV channel to a bandwidth of 6 MHz. Channels are as followed

Band III - Channels 2 to 6 (54 to 88 MHz)
Band IV - Channels 7 to 13 (174-216 MHz)
Band V - Channels 14 to 83 (470 to 890 MHz)

VHF and UHF

VHF (very high frequencies) are usually channels that include channels 2 to 13. UHF (ultra high frequencies) are channels that usually include channels 14 to 83.

Both VHF and UHF are great frequencies for carrying TV signals (both audio and video signals). They have a long range and can penetrate structures such as walls.

Higher Bands

These 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.

NTSC

All standard television signals that are transmitted in the United States follow NTSC regulations. NTSC (National Television Standards Committee) states that the video signal must have a video line resolution of 525 lines with a 3.58 MHz chroma carrier (color TV signal) and must cycle at 60 cycles per second. It also states that frames are to be displayed at 30 frames per second. NTSC standard makes it easy for all TV sets to pick up the same signals transmitted by broadcast companies. It is important to note that this standard is for analog television only.