Heinrich Hertz
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The physicist who in 1887 built a spark-gap transmitter and a loop receiver and demonstrated the waves Maxwell had predicted, turning radio from mathematics into an engineering problem.
He reportedly saw no use for the result, which is the most useful thing about the story: the distance between a demonstration and an application is not a measure of the demonstration. Within fifteen years the same effect was carrying messages across the Atlantic commercially. His name is the unit every spectrum plan, channel width and clock rate is quoted in.
Also known as: hertz