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ELI5 Yahaaa

A wobble carried on a wave

How Does Music Get Into a Radio?

A radio station sends out one steady wave and changes it slightly in time with the sound; your radio undoes the change.

A tuner that picks onewaveAn aerial that catchesall of themThe wobble is strippedback offA speaker turns it intomoving air
The wave is the carrier. The music is the wobble.

  1. Step 1 of 5

    Sound itself will not travel far.

    Sound in air Fades within a fewhundred metresA radio wave Crosses a country,needs no air

    Sound is moving air, and moving air runs out of energy within a few hundred metres. Radio waves cross a country without needing any air at all.

  2. Step 2 of 5

    The station sends one steady wave.

    A transmitter, onefixed frequency A steady carrier,carrying nothingyet

    A transmitter puts out a wave at one fixed frequency all day — its carrier. On its own it holds no information whatsoever.

  3. Step 3 of 5

    The music is added as a wobble.

    AM — height wobbles Easily spoiled byelectrical noiseFM — spacing wobbles Noise changes height,not spacing

    AM changes how tall the wave is in time with the sound. FM leaves the height alone and nudges the frequency instead, which is why FM survives interference better.

  4. Step 4 of 5

    Tuning throws almost everything away.

    1 The aerialcatcheseverything2 A circuitresonates atone frequency3 One station,loud and clear

    Your aerial picks up every station at once. The tuning dial sets a circuit to resonate at one frequency, so that station comes through strongly and the rest do not.

  5. Step 5 of 5

    Then the wobble is peeled back off.

    1 The wobble isseparated out2 A cone moveswith it3 Air pressurereaches yourear

    Stripping the carrier away leaves the original shape of the sound. Amplify that and push it through a speaker cone and the air moves as it did in the studio.

    FM broadcasts sit between 87.5 and 108 MHz — the wave wobbles about a hundred million times a second, and the music rides on top of that.

The short version

A radio station rides sound on a steady carrier wave by wobbling it, and your radio tunes to one carrier and reads the wobble back off.

Try it yourself

Tune slowly between two stations. The hiss in between is your radio faithfully amplifying a wobble that is only random noise.

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