Waves and communication

Transmitting information
1. Infrared light, microwaves and radio waves are all used to transmit information such as computer data, telephone calls and TV signals.
2. Infrared light
  1. Information such as computer data and telephone calls can be converted into infrared signals and transmitted by optical fibres. Optical fibres are able to carry more information than an ordinary cable of the same thickness. In addition the signals they carry do not weaken so much over long distances. Television remote controls use infrared light to transmit coded signals to the television set in order to, for example, change channels or adjust the volume.
3. Microwaves
  1. Microwave radiation can be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones which are in their range.
  2. Certain microwave radiation wavelengths pass through the Earth’s atmosphere and can be used to transmit information to and from satellites in orbit.
4. Radio waves
  1. Radio waves are used to transmit television and radio programmes. Longer wavelength radio waves are reflected from an electrically charged layer of the upper atmosphere. This means they can reach receivers that are not in the line of sight because of the curvature of the Earth’s surface.
Carrying analogue and digital information
1. Analogue and digital
  1. Before a sound or piece of information is transmitted, it is encoded in the transmitter in one of the ways described below - analogue or digital. The receiver must then decode the signal to produce a copy of the original information or sound.
    1. Analogue signals vary continuously in amplitude, frequency or both.
    2. Digital signals are a series of pulses with two states - on (shown by the symbol ‘1’) or off (shown by the symbol ‘0’). Digital signals carry more information per second than analogue signals and they maintain their quality better over long distances.
2. Noise
  1. All signals become weaker as they travel long distances. They may also pick up random extra signals. This is called noise, and it is heard as crackles and hiss on radio programmes. Noise may also cause an internet connection to drop, or slow down as the modem tries to compensate.
  2. An important advantage of digital signals over analogue signals is that if the original signal has been affected by noise it can be recovered more easily. In analogue signals, when the signal is amplified to return to its original height, noise gets amplified as well.
3. Analogue vs. digital - Higher tier
  1. Analogue signals
    1. Noise adds extra random information to analogue signals. Each time the signal is amplified the noise is also amplified. Gradually, the signal becomes less and less like the original signal. Eventually, it may be impossible to make out the music in a radio broadcast from the background noise, for example.
  2. Digital signals
    1. Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude than the 'on' states of the digital signal. As a result, the electronics in the amplifiers can ignore the noise and it does not get passed along. This means that the quality of the signal is maintained. This is one reason why television and radio broadcasters are gradually changing from analogue to digital transmissions. They can also squeeze in more programmes because digital signals can carry more information per second than analogue signals. Another advantage of digital signals is that information can be stored and processed by computers.
Coding and storing information
1. Coding
  1. Coding involves converting information from one form to another. All types of information can be coded into a digital signal.
  2. Digital signals are a series of pulses consisting of just two states, ON (1) or OFF (0). There are no values in between. The sound is converted into a digital code of 0s and 1s, and this coded information controls the short bursts of waves produced by a source.
  3. When waves are received, the pulses are decoded to produce a copy of the original sound or image.
2. Amount of information
  1. The amount of information needed to store an image or sound is measured in bytes (B).
  2. A megabyte is larger than a byte, and a gigabyte is larger than a megabyte.
  3. To store one minute’s worth of music it would take about 1 megabyte, to store an average two hour movie it would take 1.5 gigabytes.
  4. In general, the more information that is stored about an image or sound, the higher the quality.

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Waves and communication

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	Created by jakeogilvie over 11 years ago