5From Analogue to Digital

Historical Note1

The origins of Sampling Theory can be traced to the invention of telegraphy and efforts to maximise a telegraph line’s utilisation. Since there is a limit to how fast a telegraph operator may key-in messages, a question arose as to whether it is possible to use the same line by two or more telegraph operators. This was in effect multiplexing two or more telegraph calls on the same circuit and is known as time division multiplexing (TDM). Proposals for TDM of telegraphy are recorded as early as 1848, only 4 years after Morse’s telegraph system formally went into operation. A rotating switch (commutator) connected a telegraph line to several operators in turn, and a matching rotating switch at the receiver distributed the incoming multiple stream to listening operators. The commutators ‘sampled’ the input of operators: and the speed of sampling had to be set to a ...

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