# 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.

- **Patent:** US 2292387
- **Original title:** Secret communication system
- **Owner:** Individual
- **Granted:** 1942
- **Status:** Public domain (expired)
- **Times cited:** 82
- **Field:** telecommunications, mechanical, aerospace

## What it does

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 does NOT 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.

## Real-world examples

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

## 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.

## Frequently asked questions

### What does Hedy Lamarr and George Antheil's Frequency Hopping Secret Communication System cover?

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.

### Who owns patent US 2292387?

Individual owns this patent, granted in 1942.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 2292387 cited by?

This patent has been cited by 82 later patents that build on its ideas.

### What problem does this patent solve?

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.

### What does this patent NOT cover?

Does not cover digital frequency hopping methods using modern microprocessors.

**Full plain-English explainer:** https://patentbrief.org/patent/us/2292387/hedy-lamarr-frequency-hopping

**Original patent:** https://patents.google.com/patent/US2292387

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


## Related patents

Semantically similar inventions in the PatentBrief corpus:

- [How to Create a Secret Code Key Without Meeting First](https://patentbrief.org/patent/us/4200770/diffie-hellman-public-key-exchange) — This 1980 patent describes a way for two people to create a secret code key over a public channel, like the internet, without ever meeting or sharing the key directly.
- [How Bluetooth Creates Wireless Networks with Unique Addresses](https://patentbrief.org/patent/us/6590928/bluetooth-frequency-hopping) — This 2003 patent describes how Bluetooth devices use a master device's address and clock to create a unique, hopping radio channel for communication and build a network map.
- [CSIRO's High-Frequency Wireless Network Technology](https://patentbrief.org/patent/us/5487069/wifi-csiro-wireless-lan) — This 1996 patent from CSIRO describes a wireless local area network system that can send data reliably using radio waves above 10 GHz, even when signals bounce off walls.
- [How Marconi Patented Early Wireless Telegraphy Signals](https://patentbrief.org/patent/us/586193/radio-wireless-marconi) — Guglielmo Marconi's 1897 patent for sending electrical signals through the air to enable early wireless communication.
- [How RSA Public-Key Encryption Keeps Digital Messages Secret](https://patentbrief.org/patent/us/4405829/rsa-encryption) — This patent describes the foundational RSA algorithm, a method for securely sending messages where anyone can encrypt a message using a public key, but only the intended recipient can decrypt it using a secret private key.