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Beyond the Frequencies: Exploring the Fascinating World of Radio Waves

What radio waves are, how they were discovered and put to use, how they power GPS and weather radar, and what safety research says.

By Written Facts StaffJune 5, 2023Updated October 15, 20268 min read

You turn the key, the car radio comes on mid-song, your phone finds its route home, and the weather app warns that rain is moving in. Every one of those things arrived on radio waves. Radio waves are light whose frequency is too low for your eyes to see. They are the same kind of energy as sunlight, moving at the same speed. Here is what they are, how people learned to use them, what they do for you every day, and what the evidence says about their safety.

Light you can't see

Radio waves sit at one end of the electromagnetic spectrum, the same family that includes visible light. International rules give them an exact boundary. Under the International Telecommunication Union's Radio Regulations, radio waves are electromagnetic waves below 3,000 GHz (3 terahertz) that travel through space without an artificial guide such as a cable.

Like all light in a vacuum, they travel at exactly 299,792,458 meters per second. That figure is fixed by definition, and the meter itself is defined from it. Because the speed never changes, a wave's frequency sets its wavelength:

wavelength = speed of light ÷ frequency

Frequency is counted in hertz, or cycles per second. Wavelength is a distance, measured in meters, not a speed. Working the formula shows how much radio waves vary in size. An FM station at 100 MHz sends waves about 3 meters long. An AM station at 1,000 kHz sends waves about 300 meters long, roughly the length of three football fields. A 6 GHz Wi-Fi signal has waves about 5 centimeters long. These differences in size are why each technology lives where it does on the dial.

From a spark in Karlsruhe to an "S" across the Atlantic

The physicist James Clerk Maxwell predicted electromagnetic waves on paper. Heinrich Hertz set out to prove that they existed. In November 1886, at the Technische Hochschule in Karlsruhe, Germany, he generated and detected them in his laboratory, and he published his confirmation of Maxwell's theory in 1887. The unit of frequency, the hertz, is named for him.

Guglielmo Marconi turned the effect into a way of communicating. On December 12, 1901, at Signal Hill in St. John's, Newfoundland, he heard three faint clicks: the Morse code letter "S," sent from Poldhu in Cornwall, England, more than 2,000 miles away. The signal had reached him by bouncing off the ionosphere, a charged layer of the upper atmosphere. This showed that radio could travel beyond the curve of the Earth.

When radio started talking

Within two decades, radio carried voices and music, not just dots and dashes. At 6:00 p.m. on November 2, 1920, Westinghouse station KDKA in Pittsburgh broadcast the returns of the Harding–Cox presidential election. It was the first commercially licensed radio broadcast in the United States.

Britain followed quickly. The British Broadcasting Company, then a private company, was founded on October 18, 1922. It began daily broadcasts on November 14, 1922, from station 2LO at Marconi House in London. It became the public British Broadcasting Corporation in 1927.

Who decides what goes where

As stations multiplied, governments needed to stop them from drowning each other out. In the United States, the Communications Act of 1934, signed on June 19 of that year, created the Federal Communications Commission (FCC). Today the FCC allocates non-federal spectrum in bands running from 8.3 kHz to 275 GHz.

Those allocations are why your radio dial looks the way it does:

AM occupies 535 to 1,705 kHz, with stations placed every 10 kHz from 540 to 1,700 kHz.
FM occupies 88 to 108 MHz, divided into 100 channels, each 200 kHz wide.

Each channel is wider on FM, which leaves more room for audio. Lower AM frequencies can bounce off the ionosphere, the same effect that carried Marconi's "S" across the ocean.

The map keeps changing. On April 23, 2020, the FCC opened 1,200 MHz of the 6 GHz band (5.925 to 7.125 GHz) for unlicensed use. That space is what Wi-Fi 6E and Wi-Fi 7 routers use. AM radio still has political weight too. In September 2026, the U.S. House passed the bipartisan AM Radio for Every Vehicle Act. The bill directs the Department of Transportation to require AM radio as standard equipment in new cars, with no extra fee.

Finding your way, watching the sky, seeing inside you

Radio does more than carry voices and data.

Navigation. GPS satellites broadcast positioning signals on dedicated frequencies. These include L1 at 1,575.42 MHz, L2 at 1,227.60 MHz, and L5 at 1,176.45 MHz. Your phone listens to these signals to work out where it is.

Weather. The National Weather Service's NEXRAD network uses WSR-88D Doppler radars that transmit between 2,700 and 3,000 MHz, with wavelengths of about 10 centimeters. Waves of that size pass through rain well enough to show both how intense a storm is and how fast it is moving.

Medicine. An MRI scanner sends radio-frequency pulses tuned to the hydrogen protons in your body. As the protons settle back into line with the machine's main magnetic field, they give off radio signals of their own. The scanner detects those signals and turns them into cross-sectional images.

Is it safe?

Since phones are held against people's heads, regulators set limits. The FCC caps the Specific Absorption Rate for mobile devices sold in the United States at 1.6 watts per kilogram, averaged over one gram of tissue.

The cancer question has a mixed history, so it is worth stating precisely what has been found:

In May 2011, the International Agency for Research on Cancer classified radio-frequency fields as Group 2B, "possibly carcinogenic to humans." The basis was limited evidence on two kinds of tumor, glioma and acoustic neuroma.
The U.S. Food and Drug Administration's position is that the weight of scientific evidence has not linked radio-frequency energy from cell phones to health problems or tumors.
A 2024 systematic review commissioned by the World Health Organization and published in Environment International concluded, with moderate certainty, that mobile phone use is not associated with more brain tumors.

Wildlife raises a separate question. Research has found that human-made electromagnetic noise in the megahertz range can disrupt the compass sense of migratory birds. The leading explanation involves cryptochrome, a light-sensitive protein in the bird's retina that is thought to detect magnetic fields through a quantum effect.

From the ocean floor to the stars

At the longest wavelengths, radio can reach places other signals cannot. For decades the U.S. Navy ran Project ELF, an extremely low frequency transmitter system in Clam Lake, Wisconsin, and Republic, Michigan, used to signal submarines underwater. The Navy shut it down on September 30, 2004.

Radio has also been aimed at the stars. On November 16, 1974, the Arecibo Observatory in Puerto Rico transmitted a 1,679-bit message designed by Frank Drake toward the star cluster M13, about 25,000 light-years away. Radio travels at light speed, so the message will need about 25,000 years to get there, and any reply would take just as long to come back. No reply has ever been received, and no one beyond Earth has been confirmed to have heard us.

That message began the same way as the song in your car this morning: as a radio wave leaving an antenna at the speed of light.

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