How Radio Works
An interactive book about invisible waves, and how they carry voices, music and Wi-Fi through the air.
Table of contents
Part 1 · What a wave is
What is a wave?
Amplitude, frequency and phase: the three knobs every radio ever built turns.
Meet the sine wave
A dot going around a circle is secretly drawing radio’s favorite wave.
From ripples to radio
Electromagnetic waves, the spectrum, and why your Wi-Fi never collides with FM radio.
When waves meet
Two waves can add up to a giant — or cancel to nothing. Ask your noise-canceling headphones.
Part 2 · Putting a message on a wave
Part 3 · The journey there and back
Throwing and catching waves
How a wiggle in a wire leaps into empty space, why antenna size follows wavelength, and why tilt matters.
Fading away
Why a radio signal weakens so fast with distance: the inverse-square law, and why the bars on your phone drop.
Where the hiss comes from
The ever-present floor every signal must rise above: warm electronics, lightning, the sun and galaxy, and the faint afterglow of the Big Bang.
What stops a wave
Walls, water and metal: why some frequencies pass through, and why a microwave is safe.
Bouncing off the sky
Why far-away AM stations appear after dark: a mirror in the sky, and voices that hop around the planet.
Is any of this dangerous?
The honest answer to the Wi-Fi/5G/phone question: why radio and light pass through you but X-rays don’t.
Inside the receiver
Tuning and mixing: how a radio pulls one faint station out of a roomful of others, and how the transmitter built the wave at all.
Part 4 · From a voice to numbers
From your voice to a wiggle
A microphone turns sound into an electrical wave; a speaker turns it back. The message, made real.
The wave recipe
Every signal is secretly a stack of sine waves, and that stack is what bandwidth means.
Turning waves into numbers
What “digital” really means: snapshots in time (and the Nyquist trap), rounding each one into a number, and squeezing out the boring bits.
Part 5 · Sending bits
Bits on the air
ASK, FSK, PSK: flipping the three knobs to send ones and zeroes, and read them back.
Keeping bits honest
Manchester coding, clock recovery and the error correction that makes digital flawless.
Constellations & 64-QAM
Mix amplitude and phase to pack six bits into every symbol.
An orchestra of carriers
Why Wi-Fi sends thousands of slow symbols side by side instead of one fast stream, and why echoes don’t ruin it.
The speed limit
Lane width times headroom above the hiss: the one law that decides how fast any link can ever go, and that no cleverness can beat.
Part 6 · Sharing the air
Taking turns
Listen before you talk — and talk both ways at once: how devices share the air politely.
Hiding in the noise
Spread spectrum, frequency hopping (Bluetooth) and ultra-wideband: signals built to dodge.
Aiming the invisible
Beamforming: many small antennas nudging their phases to point energy straight at you.
A quilt of cells
Why a planet of phones needs thousands of small towers instead of one giant one, and the invisible handoff that follows you down the highway.
Anyone can listen
Radio is a shout in a public room, and anyone can record it. Why your Wi-Fi is private anyway: secret keys, scrambled bits, and locks made of math.
Part 7 · Radio as a ruler
Part 8 · The whole picture
Appendices · optional
The spinning arrow
Why engineers reach for complex numbers: the chapter-2 circle, written as one number.
The un-adding machine
Chapter 16 promised every wave is a stack of sines. Here is how anything actually un-stacks one: probe, multiply, average. The Fourier transform, with no algebra.
When waves multiply
Chapter 4 taught you to add two waves, and adding keeps the same two notes. Multiplying them breeds two brand-new ones, at the sum and the difference of the speeds, and that single trick is the hidden engine inside AM, the mixer, and the un-adding machine.
Thinking in decibels
How radio people measure signal strength, and why everything ends up in dB.
A field guide to antennas
Whips, rabbit ears, Yagis, dishes and the antennas hiding in your phone: a spotter’s guide to the shapes all around you.
Towers in the sky
Parked giants and racing swarms: how satellites, the dishes that never move, and the quarter-second pause fit the radio story.
Talking to the edge of the solar system
A twenty-watt whisper from beyond the planets, the three giant ears that catch it, and every idea in this book pushed to its limit at once.
The whistle that carries
A sensor in a field, a coin cell meant to last ten years, and a message that still arrives from miles away: how a sliding whistle trades speed for reach.
How we found the invisible
Maxwell dreamed them, Hertz proved them and shrugged, Marconi bet on them, and the Titanic made them law: radio’s story in six scenes.
Everyday radio mysteries
Why the garage door needs a second click, why the dish dies in a storm, what airplane mode is really for: a casebook of little mysteries the book can now solve.
The words, in one place
Every term the book taught you, one calm sentence each, with a pointer back to the chapter that made it make sense.