Radio waves are a type of electromagnetic radiation. They are best known for their use in communication technologies such as television, 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 usually divided into seven regions in order of decreasing wavelength and increasing energy and frequency.
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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. They range from around 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, to around 300 billion hertz, or 300 gigahertz.
Radio spectrum is a limited resource and is often compared to farmland. Just as farmers need to organize their land to get the best harvest in terms of quantity and variety, radio spectrum should be divided among users in the most efficient.
In Brazil, the Ministry of Science, Technology, Innovations and Communications manages frequency allocations across the radio spectrum.
Discovery
Scottish physicist James Clerk Maxwell developed a unified theory of electromagnetism in the 1870s. He predicted the existence of radio waves.
In 1886, Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and reception of radio waves. Hertz used simple household tools, including an induction coil and a Leyden jar (a type of capacitor consisting of a glass jar with layers of leaves inside and outside) to create waves electromagnetic.
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.
radio wave bands
The radio spectrum is generally divided into nine bands:
| Band | frequency range | wavelength range |
| Extremely Low Frequency (ELF) | <3 kHz | > 100 km |
| Very Low Frequency (VLF) | 3 to 30 kHz | 10 to 100 km |
| Low Frequency (LF) | 30 to 300 kHz | 1 m to 10 km |
| Average Frequency (MF) | 300 kHz to 3 MHz | 100 m to 1 km |
| High frequency (HF) | 3 to 30 MHz | 10 to 100 meters |
| Very high frequency (VHF) | 30 to 300 MHz | 1 to 10 m |
| Ultra High Frequency (UHF) | 300MHz to 3GHz | 10cm to 1m |
| Super High Frequency (SHF) | 3 to 30 GHz | 1 to 1 cm |
| Extremely High Frequency (EHF) | 30 to 300 GHz | 1 mm to 1 cm |
Low to medium frequencies
ELF radio waves are the lowest of all radio frequencies. They have a long range and are useful for communicating with submarines and inside mines and caves.
The most powerful natural source of ELF/VLF waves is lightning, according to the Stanford VLF Group. Waves produced by lightning can bounce back and forth between the Earth and the ionosphere.
The LF and MF radio bands include marine and aviation radio, as well as AM (amplitude modulation) commercial radio. AM radio bands are between 535 kilohertz and 1.7 megahertz.
AM radio has a long range, particularly at night when the ionosphere is best at retrieving waves back to Earth. However, it is subject to interference that affects the sound quality.
When a signal is partially blocked – for example, by a building with metal walls, such as a skyscraper – the sound volume is reduced.
higher frequencies
The HF, VHF and UHF bands include FM radio, television broadcasting, public service radio, cell phones and GPS (global positioning system). These bands typically use “frequency modulation” (FM) to encode or imprint an audio or data signal onto the carrier wave.
In frequency modulation, the amplitude (maximum range) of the signal remains constant while the frequency is varied, greater or less, at a rate and magnitude corresponding to the audio signal or data.
FM results in better signal quality than AM because environmental factors do not affect the frequency the way they do. they affect amplitude, and the receiver ignores variations in amplitude as long as the signal stays above a threshold Minimum. FM radio frequencies are between 88 megahertz and 108 megahertz.
short wave radio
Shortwave radio uses frequencies in the HF range, 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.
Around the world, there are hundreds of shortwave stations, according to the NASB. Shortwave stations can be heard for thousands of kilometers because signals bounce from the ionosphere and bounce back hundreds or thousands of kilometers from their point of origin.
higher frequencies
SHF and EHF represent the highest frequencies in the radio band. They 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 into narrow beams by satellite dishes. This allows for short-range, high-bandwidth communications to take place 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).
It can only work on line-of-sight paths, as waves tend to bounce off objects such as cars, boats, and aircraft. Since waves bounce off objects, SHF can also be used for radar.
astronomical sources
Space is teeming with sources of radio waves: planets, stars, clouds of gas and dust, galaxies, pulsars, and even black holes. By studying them, astronomers can learn 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 than it appears in visible light. Instead of seeing pointy 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 sources. A quasar is an incredibly bright galactic nucleus powered by a supermassive black hole.
Quasars radiate energy 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 more energy than the entire Milky Way.
Radio astronomers often combine several smaller telescopes into an array to make 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.