Radio waves are a type of electromagnetic radiation best-known for their use in communication technologies, such as television, mobile phones and radios. These devices receive radio waves and convert them to mechanical vibrations in the speaker to create sound waves.
The radio-frequency spectrum is a relatively small part of the electromagnetic (EM) spectrum. The EM spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency, according to the University of Rochester. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.
Radio waves have the longest wavelengths in the EM spectrum, according to NASA, ranging from about 0.04 inches (1 millimeter) to more than 62 miles (100 kilometers). They also have the lowest frequencies, from about 3,000 cycles per second, or 3 kilohertz, up to about 300 billion hertz, or 300 gigahertz.
The radio spectrum is a limited resource and is often compared to farmland. Just as farmers must organize their land to achieve the best harvest regarding quantity and variety, the radio spectrum must be split among users in the most efficient way, according to the British Broadcasting Corp. (BBC). In the U.S., the National Telecommunications and Information Administration within the United States Department of Commerce manages the frequency allocations along the radio spectrum.
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LF and MF radio bands include marine and aviation radio, as well as commercial AM (amplitude modulation) radio, according to RF Page. AM radio frequency bands fall between 535 kilohertz to 1.7 megahertz, according to How Stuff Works. AM radio has a long range, particularly at night when the ionosphere is better at refracting the waves back to earth, but it is subject to interference that affects the sound quality. When a signal is partially blocked — for example, by a metal-walled building such as a skyscraper — the volume of the sound is reduced accordingly.
FM results in better signal quality than AM because environmental factors do not affect the frequency the way they affect amplitude, and the receiver ignores variations in amplitude as long as the signal remains above a minimum threshold. FM radio frequencies fall between 88 megahertz and 108 megahertz, according to How Stuff Works.
SHF, which is affected less by the air than EHF, is used for short-range applications such as Wi-Fi, Bluetooth and wireless USB (universal serial bus). SHF can work only in line-of-sight paths as the waves tend to bounce off objects like cars, boats and aircraft, according to the RF Page. And because the waves bounce off objects, SHF can also be used for radar.
A radio telescope "sees" the sky very differently than it appears in visible light. Instead of seeing point-like stars, a radio telescope picks up distant pulsars, star-forming regions and supernova remnants. Radio telescopes can also detect quasars, which is short for quasi-stellar radio source. A quasar is an incredibly bright galactic core powered by a supermassive black hole. Quasars radiate energy broadly across the EM spectrum, but the name comes from the fact that the first quasars to be identified emit mostly radio energy. Quasars are highly energetic; some emit 1,000 times as much energy as the entire Milky Way.
Radio astronomers often combine several smaller telescopes, or receiving dishes, into an array in order to make a clearer, or higher-resolution, radio image, according to the University of Vienna. For example, the Very Large Array (VLA) radio telescope in New Mexico consists of 27 antennas arranged in a huge "Y" pattern that's 22 miles (36 kilometers) across.
Additional resources:
How crowded is the radio spectrum? Check out this frequency allocations chart for the United States.Read more about radio waves from NASA's Mission Science Tour of the Electromagnetic Spectrum.Learn more about radio telescopes from the National Radio Astronomy Observatory.This article was updated on Feb. 27, 2019 by Live Science contributor Traci Pedersen.