Radio waves are a kind of electromagnetic wave, as are microwaves, infrared, X-rays, and gamma-rays. The known use of radio waves is for communication; TV, cellphones, and radios all receive radio waves and turn them into mechanical vibrations within the speaker to create sound waves that can be heard.
Electromagnetic radiation is emitted in waves or particles at different wavelengths, and frequencies. This broad range of wavelengths is called the electromagnetic (EM) spectrum. The spectrum is separated into seven segments in order of shrinking wavelength, and rising energy, and frequency. The common categorization is radio waves, microwaves, infrared, visible light, ultraviolet (UV), X-rays, and gamma-rays.
Radio waves have the most prolonged wavelengths in the spectrum, starting from about 1 millimeter (0.04 inches) to beyond 100 kilometers (62 miles). They also have the lowest frequencies, from about 3,000 cycles for each second or 3 kilohertz (kHz) up to around 300 billion hertz, or 300 gigahertz (GHz).
Scottish physicist James Clerk Maxwell, who came up with the unified theory of electromagnetism in the 1870s, anticipated the presence of radio waves. A couple of years after that, Heinrich Hertz, a German physicist, tested Maxwell’s speculations for the creation, and reception of radio waves. The unit of frequency of an electromagnetic wave — one cycle for every second — is known as Hertz, in his honor.
Bands of radio waves
The National Telecommunications and Information Administration usually separates the radio spectrum 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|
|Medium Frequency (MF)||300 kHz to 3 MHz||100 m to 1 km|
|High Frequency (HF)||3 to 30 MHz||10 to 100 m|
|Very High Frequency (VHF)||30 to 300 MHz||1 to 10 m|
|Ultra High Frequency (UHF)||300 MHz to 3 GHz||10 cm to 1 m|
|Super High Frequency (SHF)||3 to 30 GHz||1 to 1 cm|
|Extremely High Frequency (EHF)||30 to 300 GHz|
Stanford VLF Group stated that the strongest natural source of ELF/VLF waves on our planet is the lightning. Waves created by lightning strikes can ricochet up and down between the Earth and the ionosphere, so they can travel around the planet. Radio waves are also created by artificial sources, such as electrical generators, power lines, appliances and radio transmitters. ELF radio is practical because of its huge range, and its ability to go through water and rock for communication with submarines, or inside mines. Never the less, the carrier frequency is usually lower than the frequency range of audible sound, which for us humans is from 20 to 20,000 Hz. In this case, ELF radio cannot be modulated quickly enough to create sound, that is why it is used only for digital data at a very slow pace.
LF and MF
LF and MF radio bands cover marine and aviation radio, also commercial AM radio. Most radio in these bands utilizes amplitude modulation (AM) to set an audible signal onto the radio carrier wave. The power, or amplitude of the signal, is mixed, or modulated, at a rate that matches the frequencies of an audible signal like voice or music. AM radio has a broad range, especially at night, but it is prone to interference that affects the quality of the sound. When a signal is somewhat blocked, the volume of the whole thing is decreasing accordingly.
HF, VHF and UHF bands
HF, VHF and UHF bands contain FM radio, broadcast television sound, public service radio, cellphones, and GPS. These bands usually work with frequency modulation to impress an audio or data signal onto the carrier wave. In this case, the amplitude of the signal remains consistent while the frequency is varied slightly higher or lower at a rate and magnitude matching the audio or data signal. With this, we end up with a better signal quality than AM because environmental factors do not change the frequency the way they affect amplitude, and the receiver ignores fluctuations in amplitude as long as the signal is above a minimum threshold.
According to the National Association of Shortwave Broadcasters (NASB), in the HF band frequencies, from around 1.7 MHz to 30 MHz you can find the shortwave radio. All over the globe, there are hundreds of shortwave stations, reported the NASB.
When the two-channel stereo music got popular, the demand for stereo radio broadcasting arose. Although, one-channel (monaural, or mono) radios were already in use by many and were likely to remain so for the expected future. The problem, was to make a system that could play stereo music and still be compatible with the current mono receivers at the time.
The approach approved for FM stereo broadcasting was really cleaver. The broadcaster connects the left and right channels as L + R and L − R and broadcasts them on separate frequencies, A and B. The mono receiver can lock onto A and get hear both frequencies. A stereo receiver, on the other hand, locks onto both frequencies and mixes A and B as A + B and A – B.
SHF and EHF are the highest frequencies in the radio band and are, from time to time, treated like a part of the microwave band. Molecules in the atmosphere tend to take in these frequencies, which restricts their range and use. Nevertheless, their short wavelengths let signals to be focused in narrow beams by parabolic dish antennas, so they can be efficient for short-range high-bandwidth communications between stationary locations. The less affected by air SHF is currently in use for short-range applications like Wi-Fi, Bluetooth and wireless USB. Furthermore, SHF waves have a tendency to bounce off of objects like vehicles, boats and aircraft, so those frequencies are often used for radar.
Outer space is actually filled with radio sources. Among some of those are planets, stars, gas and dust clouds, galaxies, pulsars, and even black holes. These radio waves give researchers insight about the motion and chemical structure of these sources as well as what is the cause of these emissions.
NASA reported that, radio astronomers often combine data from a few smaller telescopes, or receiving dishes, arranged into a specific way to make a clearer, higher-resolution, radio image. For instance, the Very Large Array (VLA) radio telescope in New Mexico is made out of 27 antennas organized in a large “Y” pattern up to 22 miles (36 km) across.
According to NASA, a radio telescope observes the sky very differently than it appears in visible light. Instead of capturing point-like stars, that kind of telescope looks at distant pulsars, supernova remnants and star-forming regions of space.
Quasars ( which is short for quasi-stellar radio sources ) are also detectable by a radio telescope. A quasar is a really bright galactic core fueled by a supermassive black hole. They emit energy broadly across the EM spectrum, but are named quasars, because the first of them were identified to eject mostly radio energy. They are very energetic, some give off 1,000 times as much energy as the whole Milky Way galaxy.