# AM, FM and internet radio: three different signal paths

Canonical: https://worldradionow.top/museum/articles/armstrong-fm-am-and-internet-radio/
Language: en
Author: World Radio Now
Published: 2026-10-19T12:58:04.128Z
Updated: 2026-10-19T12:58:04.128Z

Armstrong’s frequency modulation work helps explain why a station’s programme and its delivery method are different things.

## Carrying sound on a carrier

Sound varies over time. A radio transmitter can use that variation to change a carrier signal. In amplitude modulation, AM, the carrier's amplitude varies. In frequency modulation, FM, its frequency varies. A compatible receiver recovers the information and produces sound through a speaker or headphones.

This description deliberately omits many engineering details. It is a first comparison, not a claim that every radio service uses identical equipment or has identical reception quality.

## Armstrong's contribution

Edwin H. Armstrong's work on FM in the 1930s is part of a broader history of attempts to improve radio reception and handle interference. IEEE's educational material introduces that work; the Smithsonian's archival record provides another route into Armstrong's papers and career.

## Why a browser is different

An internet player receives encoded audio data across a computer network. It does not turn your phone into an FM tuner, and opening a station stream is not the same physical process as tuning a radio frequency. A broadcaster may offer both terrestrial transmissions and an online stream of the same programme.

World Radio Now focuses on finding those online station streams. The museum's [FM exhibit](/museum/exhibits/fm-radio/) helps explain the distinction, then links you back to today's live stations. Playback availability depends on the station's stream and the listener's connection.

## Sources

- [IEEE REACH: Edwin H. Armstrong, FM radio and the later years](https://reach.ieee.org/multimedia/edwin-h-armstrong-radio-pioneer-fm-radio-and-the-later-years/)
- [Smithsonian Libraries: Edwin H. Armstrong papers](https://www.si.edu/object/edwin-h-armstrong-papers:siris_sil_1100910)