How radio works

Why Edwin Armstrong developed FM radio

AM radio was popular but prone to interference and static, which could be frustrating for listeners. In 1933, Armstrong, a Columbia University professor, discovered that a clearer signal could be broadcast by revising how it was captured.

Radio waves are used in broadcasting, weather radar, telecommunications, and GPS

Its ability to bend around obstacles and reflect off the ionosphere—an electrified layer of Earth's upper atmosphere—allows this type of light to travel long distances without damaging living things due to its low energy. MRI scanners, WiFi, and Bluetooth technologies are also applications of this form of light.

How underground radio revitalized rock 'n' roll

Early FM was a wasteland and quickly became the domain of amateurs and risk-takers, including many stations and DJs who played music that flew in the face of mainstream trends. This history of the band's scrappy beginnings unpacks how it realigned the rock charts.

Stream live radio from anywhere on Earth

Spin a 3D globe and tune into thousands of live radio stations by clicking any dot on the map. The project is seamless and acts as a reminder that somewhere, right now, someone is broadcasting music, news, or a call-in show in a language you've never heard.

See a timeline of commercial radio history

Radio, as we know it, began in the 1910s. This FCC timeline traces the evolution of the medium over the century that followed, highlighting groundbreaking broadcasts, speeches, and technological breakthroughs.

1 in 5 Americans get local news from the radio

According to a 2023 Pew Research Center report, radio remains the second most popular medium for local news, remaining a vital source for local concerns. Audiences for national public radio, however, have declined, with listenership for NPR-affiliated stations down 10%.

By measuring radio signals transmitted to and received from distant spacecraft, NASA's Deep Space Network can determine a spacecraft's position and speed and send commands to alter its trajectory.

A map of religious radio stations in the US

A Pew analysis of 440,000 hours of broadcasts found more than 4,000 faith-based AM/FM stations reach 98% of American adults (out of a total of 17,000 licensed stations). Ownership is highly concentrated, with the top 30% of stations belonging to large groups; Educational Media Foundation's K-LOVE and Air1 networks alone hold hundreds of licenses nationwide.

A professor explains how podcasts built on radio's strengths

When podcasts were first produced in the early 2000s, they were often recordings of radio shows aimed at listeners who wanted to listen outside of the broadcast windows. Siobhan McHugh, an associate professor of journalism at Australia's University of Wollongong, argues that the form is built on radio's intimacy, amplifying the connection listeners feel with their favorite hosts.

Despite the popularity of podcasts, most US adults still listen to radio

A 2026 survey found that 84% of adults aged 25-64 report listening to the radio weekly. That's more than double the number of those who listen to podcasts.

Breaking down the ionosphere, which reflects radio waves from Earth's surface

Made up of ionized regions within the mesosphere and thermosphere, the ionosphere contains charged particles produced when solar radiation knocks electrons free from atoms and molecules in the atmosphere. Before satellites, radio operators would bounce signals off these regions to wrap around the planet and extend the range of transmissions.

Listen to the sounds of pulsars, which emit radio pulses up to hundreds of times a second

Just as figure skaters spin faster by tucking in their arms, these celestial objects acquire high rates of spin from the collapse of the cores of massive stars. The star's rotation spins its magnetic field, generating beams of radio waves from its magnetic poles. If either of these poles faces a detector, the signals can be picked up and converted to audio signals.

The accidental birth of radio astronomy and the benefits of a moon-based telescope

Detecting radio waves from distant celestial objects is complicated by noise from solar wind, which the nighttime side of the moon is shielded from. If lunar temperature extremes can be overcome, the environment may serve as an optimal future home for radio astronomy, a field that began in 1928 when a 30-meter-long directional antenna, mostly out of brass and wood, picked up signals from the Sagittarius constellation.

Distinguishing between natural and artificial, or induced, radioactivity

Naturally occurring radioactivity comes from radioactive elements underground, cosmic radiation from the sun and other objects in space, and radioactive atoms that make up the molecules we breathe, eat, and drink. Artificial radioactivity is predominantly generated for medical applications and industrial activities.

How do 5G base stations work?

5G relies on a combination of base stations, including macrocells, small cells, and femtocells. The differences between the three are apparent in size, coverage, and cost—but, small cells in particular are key to providing the high millimeter wave frequencies 5G promises. Learn more in this three-minute video.

Learn about the applications of radioactivity in medical, academic, and industrial settings

Besides their use for radiometric dating by archaeologists and researchers at museums and universities, radioactive materials are used in sensors that help track ocean currents and analyze pollution, soil, and petroleum products. Radioisotope-based sensors also help measure air in ice cream and prevent spillovers when soda bottles are filled in factories.

Explore a visual and auditory guide to wave properties and waveforms to learn how every sound imaginable can be created by combining multiple vibrations of air.

An overview of radioactivity, which can spontaneously change one element into another

Unstable atomic nuclei can transmute into a new element—an atom with a different number of protons—by emitting an alpha particle (two protons and two neutrons) or a beta particle (an electron). The electron can emerge from the nucleus when a neutron, which has no charge, suddenly transforms into a proton and an electron, thereby maintaining zero charge before and after the transformation, but altering the original element.

Before the invention of transistors, vacuum tubes made radio possible

Discovered by Thomas Edison, vacuum tubes allow electrical currents to travel through empty space. Later modified into a diode—keeping current flowing in only one direction—vacuum tubes allowed electronics to turn alternating current into direct current.

Try out an online tone generator, which produces sounds of specific frequencies to help tune instruments, test your hearing, and generate beats by overlapping tones.

Learn about the 'Goldilocks' of radioisotopes, which can help attack hard-to-treat cancers

Actinium-225 can be attached to a molecule that binds to cancer antigens, helping it target specific cancers in the body. It emits alpha particles that can damage DNA but do not penetrate deeply, confining the damage to nearby cancer cells. However, annual global production of actinium-225 is less than a grain of sand.

We hear because soundwaves are converted into electrochemical signals in our ears

This science teacher video systematically walks through the biology of the outer, middle, and inner ear. The explanation starts with the auricle, an external part that funnels sound through the auditory canal, and the tympanic membrane (the ear drum), which vibrates when sounds hit it. Beyond that, as the video details, is the eustachian tube, which is connected to the back of our throats and allows air to pass in and out to equalize ear pressure.

What (and why) is ASMR?

ASMR podcasts and videos are appearing all over social media, so what exactly is it, and what does it do? This immersive article explains the phenomena of ASMR, which stands for autonomous sensory meridian response. ASMR is when certain sounds or...

If a source of music traveled past someone at twice the speed of sound, assuming sufficiently sensitive hearing and powerful equipment, they would hear the music backward.

View the electromagnetic spectrum and the properties of different types of light

All forms of electromagnetic radiation, from radio waves to gamma rays, travel at the speed of light in a vacuum, but their wavelengths decrease as their frequencies increase. The light-sensitive nerve cells in the human eye are sensitive to a narrow range of values, which we observe as the spectrum of visible light.

A sound's pitch will seem to change if the listener or the source moves toward or away from the other because motion changes the time it takes each successive sound wave to reach the listener.

A government mandate changed the sound of Canadian radio

In 1971, Canadian radio stations were required to ensure their programming included at least 30% Canadian artists. The impact was both cultural and commercial, with Canadian artists gaining more visibility at home and Canadian studios and songwriters earning more pay.

During flights, cell phones can act like signal jammers as they search for service

When farther from cell towers, these devices expend more energy to emit more powerful signals, which can overwhelm any ground-based tower or radio telescope they fly past. Rather than protecting the flight, airplane mode conserves a cell phone's battery.

View the transparency of Earth's atmosphere and how it blocks most forms of light

The gases that make up Earth's atmosphere block most harmful forms of electromagnetic radiation from reaching the planet's surface, except for some ultraviolet light. Their transparency to radio waves means this form of light can reach Earth's surface, which is why most radio telescopes are ground-based rather than space-based.

An explanation of isotopes, which can help scientists trace food, water, and farming choices

Atoms of the same element have the same number of protons, but experiments showed that atoms of the same element can move through electromagnetic fields as if they had different masses. These differences in mass come from variations in the number of neutrons, which contribute to the stability of atoms by providing a buffer to the repulsion between protons.

How atomic clocks have been used to measure the universe's fundamental constants

Atoms behave according to a set of parameters that scientists have determined give reality its properties. For example, the fine-structure constant, α, quantifies the strength of interactions between charged particles. Since the light emitted by atoms as they move between energy levels is affected by α, analyzing these emissions—the basis of atomic clocks—using different atoms helps calculate α.

When a radio company was the biggest tech stock around

The Radio Corporation of America was the biggest stock during the 1920s. Originally called Marconi Wireless, the company transformed radio technology. The company pioneered broadcasting, created NBC, and became a tech giant. After remarkable growth and challenges, RCA was acquired by General Electric in 1986, marking the end of its 67-year independent existence.

Radio quiz shows took off in the '40s

The concept took hold during the Great Depression, with 50 shows on the air by 1940, because they allowed families to imagine a financial windfall was just a few questions away. Although the genre had a slight downturn during World War II, it experienced a resurgence by the end of the decade, with 200 shows on the air.

Ultrasound machines emit and receive high-frequency sound waves to construct images of the body's interior, with differences in the penetrating power of different frequencies allowing medical professionals to identify different structures.

Pierre Curie's knowledge of electromagnetism helped decipher radioactivity

Alongside his brother, he studied electric fields in crystals and the magnetic properties of substances, which required the construction of delicate electrometers. He would use this apparatus with Marie Curie to measure radioactive emissions and the presence of undiscovered radioactive elements.

By analyzing the color of starlight, astronomers can determine how fast stars within a galaxy are moving toward or away from Earth, revealing the expansion rate of the universe.

An ear doctor with hearing loss seeks to help those with hearing loss enjoy music

Alex Chern, an ear doctor who has hearing loss himself, dreams of restoring the ability to experience "all the richness and the beauty of the sound of music" for patients—not just functional hearing. Hearing aids amplify sound waves and aren't designed to work well with music that may have varied pitch and volume. Chern is studying how hearing loss and engaging with music may affect cognitive decline.

Before radio jingles arrived in the 20th century, advertisers used poetry to sell their products.

Scientists can determine the age of rocks, fossils, and other ancient samples by measuring how many radioactive atoms in the sample have decayed, a process that occurs at precise, well-known rates.

While charges consistently move in the same direction in a direct current, the flow of charges changes multiple times per second in an alternating current.

Deep Space Network sites enable nonstop communication with distant spacecraft

Each DSN complex has multiple large, sensitive antennas that can receive weak radio signals from far-off spacecraft and send commands back to them. Their amplifiers are cooled to just above absolute zero to reduce electronic noise.

At CERN's Antimatter Factory, researchers create and guide antiprotons and antielectrons together to form antihydrogen, and all these antiparticles are analyzed to help scientists study the behavior of antimatter.

Stonehenge may have functioned as an echo chamber designed to keep ceremonies secret from outsiders.

Acoustics researcher Trevor Cox discovered that Stonehenge acts like a concert hall, reflecting and amplifying sound. This video shows Cox demonstrating the effect using a scale model inside a soundproof studio.

Microwave ovens heat food by agitating certain molecules with non-ionizing light

Molecules with resonant frequencies within the microwave range vibrate, producing heat between adjacent matter, just as hands warm when rubbed together. The mesh in front of an oven's door confines the microwaves to the container, while the rotating plate allows different parts of food to travel through regions of maximum vibration.

Less common types of radioactive decay include emitting neutrons and antimatter

Through neutron emission, one or more neutrons are ejected from atoms that have far fewer protons. Neutrons can also be released by artificially inducing the fission, or separation, of a large atomic nucleus into smaller ones. During beta-plus decay, a positron—the antimatter version of an electron—is produced when a proton turns into a neutron.

The Deep Space Network is an array of giant radio antennas at three locations on Earth to keep NASA in constant communication with spacecraft billions of miles away.

The disputed inventor of the radio

Guglielmo Marconi was awarded the 1909 Nobel Prize in physics for inventing the wireless telegraph, which used radio waves to transmit Morse code. Nikola Tesla, however, was experimenting with radio waves in the 1890s, though much of his work was destroyed in a 1895 fire.

Marfa, an art colony in the West Texas desert with a population of around 2,000, has its own NPR affiliate.

The three smallest bones in the human body—the malleus, incus, and stapes—amplify the vibrations of sound waves by almost 20 times to help enable hearing.

Noise-canceling headphones use a microphone to identify external sounds, which are then used to produce an out-of-sync version of those sounds to cancel them in your ears.