2.10 Analogue and Digital Signals
With the rise of worldwide data communications and the need to use telephone systems with computers there has been a trend towards digitising these networks. Originally, the telephone system was set up to work with normal voice traffic, with a person’s voice being converted to an electrical signal for transmission over the line and then converted back to sound at the other end. The different sounds made by a voice being represented by changes in voltage on the telephone line. This is an example of an analogue signal.
With a digital signal there are only ever two states required to be sent: ones and zeros. These states can be represented by voltages, eg: +5 volts for binary 1 and 0 volts for binary 0. The type of signal that the computer works with is digital. A digital signal is known as a square wave.
Telephone lines were designed for analogue transmission and this makes them well suited to their original purpose, ie: real time voice messages. However, data coming from a computer or terminal is in digital form, ie:: it is composed of a string of zeroes and ones.