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.
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.