AM, FM and internet radio: three different signal paths

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 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.