the signal · draw · EP-027

How Does a Radio Signal Actually Travel? (And Why Does It Fail?)

The air is full of voices.

General education, not professional advice. Where this page names a guideline body, that body's current guidance governs; where it names a next step, take it. Nothing on this page is sponsored.

Study III — The Signal.

the draw

What this draw covers.

Why does FM die in a canyon while AM rides for hundreds of miles at night? Why is your phone a radio, and what has really happened when the tower goes dark? This is the radio literacy nobody taught you — frequency, line of sight, skywave, repeaters, and the myth about power that empties wallets — ending with a twenty-five dollar proof you can hold in your hand.

What follows is the draw as spoken, line by line, with the gold line that sat under each.

On this page: the draw, in order · the rep · sources

as spoken

The draw, in order.

  1. The air is full of voices.

    Hold still a moment. The air in the room where you sit is full of voices — music, weather warnings, a thousand phone calls — passing through the walls, through the chair, through you. You were never taught to hear them. Let us fix that.

  2. Frequency is a rhythm, counted.

    A radio wave is not a mystery. It is a rhythm — a pulse of electric and magnetic push, repeating so many times each second. That count is the frequency, and its unit is the hertz: one wave per second.

  3. AM in millions, phones in billions.

    An AM station pulses around a million times a second — a thousand kilohertz. FM runs near a hundred million — megahertz, 88 to 108 on your dial. Your phone beats faster still, up in the ultra-high frequencies, hundreds of millions to billions.

  4. Wide channels, rich cargo.

    Here is the first law of the whole craft, and it is a trade. A wide channel carries more than a narrow one, and the wide channels live up in the fast frequencies. That is why your phone can carry video and an AM station carries a voice.

  5. The fast wave flies; the slow wave flows.

    But the fast wave pays for its cargo. High frequencies travel like a thrown stone — straight, and not far past what they can see. Low frequencies travel like a slow flood, bending around hills, hugging the curve of the ground.

  6. Reach and richness pull against each other.

    So the second law: reach and richness pull against each other. A video call struggles to cross a ridge. It is not broken. It is keeping the bargain its frequency made.

  7. Radio wants an unbroken view.

    Now the earth itself enters the story, because the earth is round and radio mostly is not. From FM's neighborhood upward, a signal wants line of sight — an unbroken view from one antenna to the other.

  8. Three miles at head height.

    And the horizon is closer than you think. Stand with a handheld radio at head height and your radio horizon is roughly three miles. Put the antenna on a hundred-foot tower and it stretches to around a dozen. The rule underneath: the horizon grows with the square root of the height.

  9. A canyon is a radio shadow.

    This is why FM dies in a canyon. Those waves barely bend around rock. Drop below the ridgeline and you are standing in a radio shadow, as surely as if you had stepped behind a wall at noon.

  10. At night, the sky becomes a mirror.

    And it is why AM turns strange and wonderful after dark. By day, a low layer of the upper air soaks up AM signals that travel skyward. At night that layer fades, and the higher sky turns to a mirror.

  11. Skywave: the ballgame from three states off.

    The signal leaps up, glances off, and comes down hundreds of miles away. This is skywave — why a farm truck at midnight pulls in a ballgame from three states off. Not magic.

  12. A listener on high ground.

    Now, the repeater — the beacon-keeper of the radio age. It is a simple servant on high ground: it listens on one frequency and repeats what it hears on another, instantly.

  13. Each reaches the hill; the hill reaches all.

    Two handheld radios in rough country might reach a mile or two between them. Through a repeater on a mountain, each only has to reach the mountain — and the mountain reaches everyone. Height, shared.

  14. Your phone is a weak, polite radio.

    Which brings us to the radio you carry every day and never call one. Your phone is a small, polite, rather weak radio, whispering to a tower that is usually within a few miles.

  15. Your radio is fine; the hilltop is empty.

    So when the network fails, hear what has actually happened. Your radio is fine. The other end of the conversation is gone — the tower dark, or drowned in ten thousand voices at once. You are a signaler whose partner left the hilltop.

  16. Quadruple the watts to double the reach.

    Now the myth that empties wallets: more power fixes it. It rarely does. Power fights a losing arithmetic — on paper you must quadruple the watts to double the reach, and over real ground it is worse than that.

  17. Height is might.

    Doubling your power is barely a shade louder at the far end. But raise the antenna, or clear its view, and whole miles of new country open at once. The old operators say it plainly: height is might.

  18. Ask about the view before the watts.

    So when a signal fails you, ask the questions in order. What is blocking the view? How high is each antenna? Is the channel drowned in traffic? Power comes last, because power was rarely the problem.

  19. Distance, terrain, congestion, or power.

    And know the common ways a link dies: distance, when the far end sits past your horizon; terrain, when something solid stands in the path; congestion, when too many talk at once; and power loss. Name which one you face, and you already know what to try.

  20. Seven channels, always speaking.

    Here is your proof that all of this is real, and it costs almost nothing. In America, the weather service runs towers on high ground broadcasting the weather without pause, day and night, on seven channels near 162 megahertz — from 162.400 to 162.550.

  21. No account. No internet. A receiver.

    Check whether one of them reaches where you live. It does not need your phone, your account, or the internet. It needs a receiver — and a twenty-five dollar weather radio is exactly that.

the rep

Prove you can hear it.

So here is the one thing you do today. Look up your local weather-radio frequency, get a cheap receiver into your hands, and prove you can hear that voice. The day you catch it, you stop believing in radio and start knowing it.

The well is deep. Bring a bucket.

drawn from

Where it comes from, and where it stops.

Drawn from: the plain physics of electromagnetic propagation (frequency and bandwidth, line-of-sight behavior of VHF and above, diffraction of low frequencies, ionospheric skywave at night); public US broadcast allocations (AM 540–1700 kHz, FM 88–108 MHz); NOAA Weather Radio's seven public VHF frequencies (162.400–162.550 MHz); standard radio-horizon geometry. All plain fact.

General education, not professional advice. Where this page names a guideline body, that body's current guidance governs; where it names a next step, take it.

read alongside it

From the shelf.

As an Amazon Associate I earn from qualifying purchases. The commission costs you nothing and bought none of these; the whole shelf is on the reading page, and how that works is on the about page.

  1. The ARRL Handbook for Radio Communications — ARRL

  2. The Prepper's Communication Handbook — Jim Cobb

  3. The Guerrilla's Guide To The Baofeng Radio — NC Scout

keep drawing

More from The Signal.

drink deep

The rest of the bucket.

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