Hedy Lamarr co-patented frequency hopping, but she didn't invent it.
In 1942 the film star Hedy Lamarr and the composer George Antheil patented a way to stop enemies jamming radio-guided torpedoes: hop between 88 frequencies, synchronised like a piano roll. It is a great story and a real achievement. But the idea of hopping frequencies goes back to Nikola Tesla in 1903.
Frequency hopping means a transmitter rapidly switches its signal between many frequencies in an order known only to it and the receiver. Anyone listening on a single frequency catches only fragments, and jamming one channel spoils only a brief slice of the message. The technique also lets many devices share the same band with little interference.
Its history is long. A 1903 US patent awarded to Nikola Tesla describes a signalling method that alludes to the idea, and the radio pioneer Jonathan Zenneck discussed it in a 1908 book, noting that the German company Telefunken had already tried it. The German military used frequency hopping in the First World War to keep British forces from eavesdropping, and further patents followed in the 1920s and 1930s.
Lamarr and Antheil's contribution, patented in 1942, was a specific scheme for torpedo guidance, using a piano-roll-style mechanism to switch among 88 frequencies. They gave the patent to the US Navy. The idea may have been rediscovered in the 1950s, when engineers at Sylvania built a similar system using the newly invented transistor instead of clockwork, and the US Navy used it during the Cuban Missile Crisis in 1962.
Today frequency hopping is everywhere. Military radios hop according to secret keys. In the US, rule changes allowed it in the unlicensed 2.4 gigahertz band, and many consumer devices there now use hopping modes, as do walkie-talkies and the controllers for model cars, planes and drones, letting hundreds of them work side by side. Lamarr's story deserves telling, but as one chapter in a longer tale, not its beginning.
Source: Wikipedia — Frequency-hopping spread spectrum · Text summarised from Wikipedia (CC BY-SA 4.0)
