What are radio waves? | Live Science


Radio waves are a type of electromagnetic radiation best known for its use in communication technologies, such as televisions, cell phones, and radios. These devices receive radio waves and convert them into 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. Common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays, and gamma rays.

According to NASA, radio waves have the longest wavelengths in the EM spectrum, ranging from about 0.04 inches (1 millimeter) to over 62 miles (100 kilometers). They also have the lowest frequencies, from around 3,000 cycles per second, or 3 kilohertz, down to around 300 billion hertz, or 300 gigahertz.

Radio spectrum is a limited resource and is often compared to agricultural land. Just as farmers must organize their land to get the best harvest in terms of quantity and variety, radio spectrum must be allocated among users in the most efficient way, according to the British Broadcasting Corp. (BBC). In the United States, the National Telecommunications and Information Administration of the United States Department of Commerce manages frequency allocations along the radio spectrum.


Scottish physicist James Clerk Maxwell, who developed a unified theory of electromagnetism in the 1870s, predicted the existence of radio waves, according to the National Library of Scotland. In 1886, Heinrich Hertz, a German physicist, applied Maxwell’s theories to the production and reception of radio waves. Hertz used simple homemade tools including an induction coil and a Leyden jar (an early type of capacitor consisting of a glass jar with layers of foil inside and outside) to create electromagnetic waves. Hertz became the first person to transmit and receive controlled radio waves. The unit of frequency of an EM wave – one cycle per second – is called a hertz, in his honor, according to the American Association for the Advancement of Science.

Radio wave bands

The National Telecommunications and Information Administration generally divides the radio spectrum into nine bands:

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Bandaged Frequency range Wavelength range
Extremely Low Frequency (ELF) >100km
Very low frequency (VLF) 3 to 30kHz 10-100km
Low frequency (LF) 30 to 300kHz 1m to 10km
Medium Frequency (MF) 300kHz to 3MHz 100m to 1km
High frequency (HF) 3 to 30MHz 10 to 100 meters
Very High Frequency (VHF) 30-300MHz 1 to 10 meters
Ultra High Frequency (UHF) 300MHz to 3GHz 10cm to 1m
Super High Frequency (SHF) 3 to 30 GHz 1 to 1cm
Extremely High Frequency (EHF) 30 to 300GHz 1mm to 1cm

Low to mid frequencies

ELF radio waves, the lowest of all radio frequencies, have a long range and are useful for penetrating water and rock to communicate with submarines and inside mines and caves. According to the Stanford VLF Group, the strongest natural source of ELF/VLF waves is lightning. Waves produced by lightning can bounce between Earth and the ionosphere (the atmospheric layer with a high concentration of free ions and electrons), according to Phys.org. These disturbances caused by lightning can distort important radio signals transmitted to satellites.

The 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 and 1.7 megahertz, according to How Stuff Works. AM radio has a long range, especially at night when the ionosphere better refracts waves back to earth, but it is subject to interference which affects 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.

Higher frequencies

The HF, VHF, and UHF bands include FM radio, television sound, public service radio, cell phones, and GPS (global positioning system). These bands generally use “frequency modulation” (FM) to encode or imprint an audio or data signal onto the carrier wave. In frequency modulation, the amplitude (maximum extent) of the signal remains constant while the frequency varies higher or lower at a rate and amplitude corresponding to the audio or data signal.

FM gives better signal quality than AM because environmental factors do not affect frequency the same way they affect amplitude, and the receiver ignores variations in amplitude as long as the signal stays above it. of a minimum threshold. FM radio frequencies are between 88 megahertz and 108 megahertz, according to How Stuff Works.

short wave radio

Shortwave radio uses frequencies in the HF band, from about 1.7 megahertz to 30 megahertz, according to the National Association of Shortwave Broadcasters (NASB). Within this range, the shortwave spectrum is divided into several segments, some of which are dedicated to regular broadcast stations, such as Voice of America, British Broadcasting Corp. and Voice of Russia. Around the world, there are hundreds of shortwave stations, according to the NASB. Shortwave stations can be heard thousands of miles away because the signals bounce off the ionosphere and bounce hundreds or thousands of miles from their point of origin.

Highest frequencies

SHF and EHF represent the highest frequencies in the radio band and are sometimes considered part of the microwave band. Molecules in the air tend to absorb these frequencies, which limits their range and applications. However, their short wavelengths allow signals to be directed in narrow beams by satellite dishes (satellite dishes). This enables short-range, high-bandwidth communications between fixed locations.

SHF, which is less affected by air than EHF, is used for short-range applications such as Wi-Fi, Bluetooth, and wireless USB (universal serial bus). SHF can only work on line-of-sight paths because the waves tend to bounce off objects like cars, boats and planes, according to the RF page. And because waves bounce off objects, SHF can also be used for radar.

Astronomical sources

Outer space is full of sources of radio waves: planets, stars, clouds of gas and dust, galaxies, pulsars, and even black holes. By studying them, astronomers can learn more about the movement and chemical composition of these cosmic sources as well as the processes that cause these emissions.

A radio telescope “sees” the sky very differently from what it appears in visible light. Instead of seeing point 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 nucleus powered by a supermassive black hole. Quasars radiate energy widely across the EM spectrum, but the name comes from the fact that the first quasars to be identified primarily emit radio energy. Quasars are very energetic; some emit 1,000 times more energy than the entire Milky Way.

According to the University of Vienna, radio astronomers often combine several smaller telescopes, or receiving dishes, into an array to create a clearer or higher-resolution radio image. For example, the Very Large Array (VLA) radio telescope in New Mexico consists of 27 antennas arranged in a huge “Y” pattern 36 kilometers in diameter.

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This article was updated on February 27, 2019 by Live Science contributor Traci Pedersen.


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