The encyclopedia · Engineering & Operations · Technical decision · 1941–1990s
Lamarr and Antheil hopped radio frequencies so a signal could not be jammed
Hedy Lamarr and George Antheil patented a way to keep a radio signal from being jammed, an idea that underpins modern wireless.
Hedy Lamarr and George Antheil
the move
A radio-guided torpedo was easy to disrupt: jam the single frequency it was using and the guidance failed. The obvious response, stronger signals, could be overpowered, so a different kind of solution was needed.
Hedy Lamarr and composer George Antheil had both the idea and a mechanical way to make it work. Their transmitter and receiver would both switch among a set of frequencies according to a shared code, and the code was carried on slotted paper rolls, the same mechanism that made a player piano change notes.
Sender and receiver hopped together, while an outsider heard only scattered bursts and a jammer could not tell which frequency would be used next. The message could be sent without being detected, decoded or blocked.
The insight was to treat the changing channel itself as the security, rather than the strength of the signal.
why it works
- Hopping among frequencies means a single-frequency jammer cannot cover the whole band at once.
- The synchronized code means only the intended receiver can follow the pattern, so the signal stays private.
- The same idea works whether the goal is to hide a message or to make it hard to block, so it is broadly useful.
- Using a cheap mechanical device to carry the code let it be implemented at the time, not just imagined.
what transfers
Make the signal's own route the secret — hiding in movement across a broad band defeats an attacker who can only watch one spot.
what came after
Although the US Navy did not adopt the patent for years, the concept of frequency hopping became a foundation of spread-spectrum communication. Military, and later civil, systems used the same idea, and it is partly why modern technologies like Wi-Fi and Bluetooth reject interference so well.
references
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