Science & Technology in Action

14th Edition

Changing from analogue to digital

Commission for Communications Regulations

The early telecommunications systems were digital, that is, the signals typically consisted of short or long pulses with gaps in between. Generally, only two levels were used: ‘on’ and ‘off’; in other words, they were binary systems. The most enduring and useful of those early systems was Morse code which continued in commercial use from about 1850 to about 1990.
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Lesson excerpt

Early developments

Following Alessandro Volta’s invention of the battery in 1800 scientists in Europe and beyond started exploring the properties of electricity and its possible uses. That year the heating effect of electric current and its chemical effect (electrolysis) were discovered.

In 1804 Campillo (in Spain) devised a system with about 35 wires (one for each letter etc.) connected to a set of tubes of dilute acid at the receiving end. When the sender connected a battery to the wires at one end, bubbles appeared in the corresponding tube at the other end. An improved version was made by von Sömmering in 1809 which operated over a distance of a few kilometres. However, these electrochemical systems were complicated, slow and unreliable. In 1820 the potential of long distance electric communication improved greatly with the accidental discovery of the magnetic effect of electric current by Oerstedt. Over the following 25 years or so several electromagnetic communication systems were devised, generally using several wires. The first public telegraphy company in the world — the Electric Telegraph Company — was established in England In 1845. Meanwhile other systems were devised in the United States. Samuel Morse devised a coding system for the letters of the alphabet and numerals. Each letter was represented by a series of short and long pulses (usually called ‘dots’ and ‘dashes’). Morse’s system needed only one signal wire (along with a ground ‘wire’). An added advantage of his code was that messages could be sent at sea using lamps.

By 1851 Morse code was effectively the international standard telecommunications system and remained in widespread use for over 100 years. (In fact it was used as an international standard for maritime distress calls until 1999.)

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True or False?

  1. A digital signal has can have only two possible values. false
  2. Electricity was used for telecommunications within a few years of the invention of the battery. true
  3. The magnetic effect of electricity contributed greatly to early telecommunications. true
  4. From around 1840 Morse code was used to transmit short text messages. true
  5. Early telephones (1870s) used digital technology. false
  6. In computers and digital electronics data are represented in binary form. true
  7. Digital signals can have any value from zero to 5 volts. false
  8. The first transatlantic phone call was made in 1866. false
  9. The change from analogue TV to digital TV began during the 1990s. true
  10. The first generation mobile phones were analogue. true
  11. FM radio stations in Ireland transmit only digital data. false