Hedy Lamarr and George Antheil's Frequency Hopping Secret Communication System

A 1942 patent for a radio-controlled torpedo guidance system that used synchronized player piano rolls to hop between frequencies, preventing enemies from jamming the signal.

What it covers

The system uses two synchronized mechanisms, similar to those found in player pianos, to change the carrier frequency of a radio transmitter and receiver simultaneously. By rapidly switching frequencies in a predetermined sequence, the signal becomes extremely difficult for an adversary to detect or jam. The patent describes using perforated paper rolls to control the timing of these frequency shifts, ensuring both the sender and receiver stay perfectly aligned.

What it doesn't cover

• —Does not cover digital frequency hopping methods using modern microprocessors.
• —Does not cover encryption or scrambling of the actual message content.
• —Does not cover non-mechanical methods of frequency synchronization.
• —Does not cover the use of radio waves for anything other than remote control of a torpedo.

The clever bit

The inventors realized that if you can't stop an enemy from jamming a single frequency, you should simply move the conversation to a new channel before they can react, using a shared 'rhythm' to stay in sync.

Why it matters

This invention laid the conceptual foundation for modern spread-spectrum communication. It is the core technology behind Wi-Fi, Bluetooth, and GPS, proving that frequency hopping could make wireless signals resilient against interference.

Real-world examples

• 1.Modern Wi-Fi routers
• 2.Bluetooth device pairing
• 3.Military secure radio communications
• 4.GPS signal transmission