7Digital Modulation

Historical Note

Discrete data telecommunications require technologies similar to analogue signals as data need to be transmitted over a physical medium using electrical currents or electromagnetic waves. Modulation of discrete data onto a carrier signal dates back to electrical telegraphy and on–off keying: a telegraph key (pictured)1 connects and disconnects the flow of electricity and through this process information is communicated [1]. The word ‘key’ defines to this day the digital modulation techniques used to transmit discrete signals.


Modulation of discrete data onto an electromagnetic wave carrier was shown by Guglielmo Marconi (pictured)2 in 1895. His experiments led to the development of the wireless telegraph, and he is famously credited as the inventor of wireless telecommunications. The technique ...

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