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Wireless devices crowd out cosmic radio signals and more

Author: Kathryn Hulick / Source: Science News for Students

pulsar dot
pulsar dot

This young pulsar — or spinning, ultradense star (large white dot in center right) — is not far outside our Milky Way. Some details of such celestial bodies are not visible. They come only from radio transmissions, which can be masked by Wi-Fi signals on Earth.

Cell phones, self-driving cars and virtual-reality headsets have something in common. They all send radio waves through the air. Our bodies can’t feel these invisible signals, says Scott Ransom. “We can’t hear them. We can’t see them. But all our devices are using them,” notes this astronomer who works at the National Radio Astronomy Observatory. It’s in Charlottesville, Va.

Radio waves are a type of electromagnetic radiation. This spectrum of energy also includes the light we can see, along with X-rays and ultraviolet light. But radio waves have much lower energy than these other signals. That means radio signals travel through the air as very long, stretched-out waves.

These waves can carry many types of information. They bring music from a broadcast station into your car. They carry text messages from a friend’s phone through a series of cell towers, and finally to your screen. A self-driving car sends out radio waves to help it scan for obstacles.

Often, these signals zip past each other with no problem. They’re like cars traveling on separate highway lanes, explains Paul Tilghman. He’s an engineer who specializes in wireless communication. Tilghman works for DARPA, the Defense Advanced Research Projects Agency, in Arlington, Va. That “highway” is the radio spectrum, he says. Each lane is a different radio wavelength. Each wavelength corresponds to a frequency. The number of your favorite radio station is also its frequency (in megahertz). And every device, from a tablet to a Wi-Fi-connected toy robot, has an assigned lane on the radio highway, notes Tilghman.

Story continues below image.

radio spectrum
Here’s how U.S. lanes on the radio spectrum “highway” are currently divided up. Big blue sections are reserved for television and radio broadcasting. A few bright yellow slivers are for radio astronomy.

For a long time, dividing the radio spectrum like an enormous highway has worked. But now there’s a problem. More and more devices want to be on the road, and there are only so many lanes. In many places, the spectrum is so clogged that it’s like a real highway at rush hour.

Scientists need room on that overcrowded highway, too. Ransom and other astronomers tune in to radio waves from space. Other scientists use radio waves to study Earth’s surface. Some parts of the radio spectrum are very important to this work. So devices such as cell phones and Wi-Fi routers are supposed to steer clear of those lanes.

At times, though, signals accidentally stray from their assigned lanes. If two signals try to travel in the same lane at the same time, they may jostle each other. This causes a mixed-up signal. It’s a problem known as interference. It can ruin a scientist’s data. It has been causing problems for phone companies and militaries, too.

But it doesn’t have to be that way. In fact, a growing cadre of researchers are now at work. Their goal: developing a better way for everyone to share those radio highways.

Welcome to the quiet zone

radio telescope
This telescope in Green Bank, W.Va., collects radio waves from outer space. The observatory exists in a community that observes radio silence. The reason: Signals from other radio sources, such as cell phones and the internet, can interfere with radio signals from space.

Astronomers build their telescopes in remote parts of the world. One reason is to get away from signals that may mess up their data. A lush valley in Green Bank, W.Va., is one such spot. It’s in a National Radio Quiet Zone. That means cell phones, Wi-Fi and other devices that send out radio waves aren’t allowed. People must use old-fashioned phones and computers that send signals through cables that plug into the wall.

In Green Bank, a set of telescopes collects radio waves from outer space. These signals help astronomers better understand the universe. The astronomers often listen for those signals using the parts of the spectrum reserved for science. But many of the objects they want to observe emit radio waves over much broader sections of the spectrum than have been reserved for them.

Ransom uses the Green Bank radio telescopes to study pulsars — collapsed stars that spin. He tunes in to thousands of wavelengths at once. It’s like listening to thousands of radio stations at the same time, he explains.

By the time signals from a distant pulsar reach Earth, they’re incredibly faint. The big, powerful telescopes at Green Bank can capture these signals. “They have the ability to listen to the tiniest little bits of energy,” says Ransom.

But a telescope sensitive enough to listen to a distant pulsar will also pick up any stray signal nearby. Despite the strict radio-quiet-zone rules, signals often sneak in. Electric fences are one common source, Ransom says. When a blade of grass touches the fence, it creates sparks and sends out a burst of radio waves. Spark plugs — devices inside cars that keep their engines running — cause a similar burst.

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