Data transmission

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 against the background noise, for example.

Digital signals are a series of pulses consisting of just two states: ON (1) or OFF (0). There are no values in between. DAB radio is Digital Audio Broadcast radio - it is transmitted as digital signals. The diagram shows a typical oscilloscope trace of a digital signal.

All signals become weaker as they travel long distances, and 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.

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 against the background noise, for example.

Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude than the amplitude of the ON states. 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, which is one reason why television and radio broadcasters are gradually changing from analogue to digital transmissions.

We cannot see infrared radiation, but we can feel it as heat energy. Infrared sensors can detect heat from the body. They are used in: security lights burglar alarms. Infrared radiation is also used to transmit information from place to place, including: remote controls for television sets and DVD player data links over short distances between computers or mobile phones.

Information such as computer data and telephone calls can be converted into electrical signals. These can be carried through cables, or transmitted as microwaves or radio waves. However, the information can also be converted into pulses of infrared radiation and transmitted by optical fibres. Optical fibres can carry more information than an ordinary cable of the same thickness. The signals in optical fibres do not weaken as much over long distances as the signals in ordinary cables. Optical fibres can carry more data because of multiplexing. This is where several digital signals are interleaved or carried together without being mixed. Digital radio and TV broadcasts also carry more data than analogue broadcasts: they can also be multiplexed. This allows for a more efficient use of the available radio frequencies, for example to carry many more channels or to allow high-definition (HD) television and ‘red button’ options.