Origin

The technology arrived before the idea. Wireless transmission was well understood as a way of sending messages between two points; broadcasting deliberately to an unknown audience was the genuinely new thought.

Westinghouse was granted the first US broadcasting licence on 27 October 1920 for the station KDKA in Pittsburgh, which began scheduled programming with the Harding–Cox presidential election returns on 2 November 1920.

The detail that says most about the era: results were telephoned over from a newspaper office and read into a microphone, and between them, someone played a phonograph into that same microphone to fill the gaps.

How it worked

A transmitter takes an audio signal and rides it on a much higher-frequency carrier wave. The receiver does the reverse: it tunes to one carrier out of the many arriving at the aerial, strips the carrier away and leaves the audio behind.

Tuning is the part everyone remembers physically. Turning the dial retunes a circuit so it responds strongly to one frequency and weakly to its neighbours — which is why stations arrive gradually, why they drift, and why you could sometimes hear two at once.

Valves did the amplifying for the first few decades, which is why early sets are warm, heavy, and need a moment before they make a sound.

The golden years

For roughly three decades the radio was the largest piece of furniture in the room and the reason people sat together facing the same direction. Programming was scheduled, so listening was scheduled too.

Transistors changed the shape of it. A set that ran on a small battery and fitted in a hand could go to the beach, into a bedroom, onto a building site — and radio stopped being something a family did together and became something a person did alone.

Radio also decided what became popular. For most of the twentieth century, whether a record sold depended heavily on whether it was played on air.

What came next

FM brought better fidelity and, eventually, stereo, which is why music migrated there while speech stayed comfortable on AM. Later, radio became a feature inside other things — the car dashboard, the hi-fi tuner, the clock by the bed.

Streaming has taken much of the function, but not all of it. A station still offers the one thing an algorithm imitates rather than provides: somebody choosing.

Names that mattered

Listed because of what they did, not as recommendations. Velorex Music did not make any of these.

Did you know?

• KDKA transmitted its first scheduled programme at 100 watts — less power than many kitchen appliances.
• That first broadcast ran roughly eighteen hours, from a wooden shack on the roof of a Westinghouse plant.
• The station traces back to 8XK, an experimental amateur station licensed to Westinghouse engineer Frank Conrad in 1916.
• Early listeners often used headphones rather than a loudspeaker, because the signal was too weak to fill a room.