You can freely build on How Edwin Armstrong Invented the Superheterodyne Radio Receiver
This patent expired in 1939. Every claim — 0 independent, 0 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Individual
Patent granted
1920
Expired
1939
Forward citations
31
What this patent covers
The patent describes a method for receiving high-frequency radio signals by converting them into a lower, intermediate frequency before processing. By mixing the incoming signal with a locally generated oscillation, the device creates a beat frequency that is easier to amplify and filter. This process allows a radio to isolate a single broadcast station from the crowded airwaves without losing signal quality. It essentially acts as a high-precision filter for invisible radio waves.
What is now free to use
All 0 claims of US 1342885 are in the public domain. Specifically:
The 0 dependent claims add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
Does not cover the basic concept of radio transmission itself.
Does not cover digital signal processing or software-defined radio techniques.
Does not cover the vacuum tube hardware components themselves, only the circuit arrangement.
Who is building on this today
While the original patent has long expired, the superheterodyne principle remains a core concept taught in electrical engineering and utilized by major semiconductor companies like Texas Instruments and Analog Devices in modern RF front-end designs.
Products built on expired version of this technology
AM/FM radio receivers
Television tuners
Radar systems
Early satellite communication equipment
How to cite this patent in your documentation
Individual. US Patent 1342885. Method of receiving high-frequency oscillations. Granted 1920, expired 1939. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.