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  Multiplexing, in electrical engineering, is the technique of sending multiple signals along a single wire either in one or opposite directions. It was first conceived in USA in the 1850s for use on the developing telegraph network, and was a form of time division multiplexing (TDM). Using this system the signal capacity of the telegraph lines could be greatly increased without the laborious and expensive refitting of new wires.

TDM works on the principle of allocating each signal a specific time slot in a transmission period, and ensuring that each such period is short enough to guarantee coherent communication. The first practical TDM system widely implemented was developed by the Frenchman Baudot in 1874.

A more recent form of multiplexing, frequency division multiplexing (FDM), appeared during World War I due to early work on radio transmission. It required the introduction of signal modulation and carrier frequency transmission to become viable, and used signals broadcast at separate and non-interfering frequency bands to achieve an increase in transmission capacity.

At present TDM is widely used in digital communications, while FDM is used each time our radio is tuned to a different frequency and radio station. AC



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