In 1876, Alexander Graham Bell invented a 'talking device' which could transmit a human voice to a listener.
However, Bell's device produced an extremely weak flow of audio current from the sending device, accompanied by a high level of static that made it difficult to hear. Research in transmitters continued until in 1878 Thomas Edison invented the carbon transmitter, a more practical device with much better characteristics which is still used today. The principle of the receiver has not changed.
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