Radio Waves

Radio Waves are a range of frequencies within the spectrum of light — a type of electromagnetic radiation (EMR) — found throughout the world. They are generated whenever a charged particles are accelerated, thus there is radio noise that results from lightning strikes, and radio frequencies emitted by stars, galaxies, and other cosmic objects.

Radio waves are the frequencies of light that have the longest wavelengths of all EMR, corresponding to the lowest energy frequencies of the entire electromagnetic spectrum. They are generally classified as any wavelengths with a frequency below 300 GHz (gigahertz), which corresponds to a wavelength greater than 1 mm (${3}{64}$ inch).

Radio waves are central to modern technology. They are generated whenever a charged particle is accelerated, which we accomplish in modern technology with a device called a transmitter which routes the electrical signal through an antenna, which then radiates (“broadcasts”) that information into the air where it can be picked up by other antennas connected to radio receivers.

Radio waves are used both fixed and mobile radio communication, broadcasting, radar, radio navigation, wireless networks (wifi), communications satellites, and many more functions.

Properties

Like all forms of light, radio waves travel at the speed of light, $\mathbf{c}$, when moving in a vacuum.

The range of radio waves being < 300 GHz is a relatively large division, and not all radio waves within that range have the same properties. Different frequencies / wavelengths can have different propagation characteristics.

Ground Waves are very long radio waves (with a low frequencies, and long wavelength) and diffract very well around obstacles. Skywaves are shorter waves (smaller wavelength and higher frequency) and do not diffract nearly as well as ground waves, thus have a tendency to bounce off obstacles rather than bend around them like flowing water like ground waves.

One of the benefits of this is that they bounce off the ionosphere of the Earth’s atmosphere, thus can be used to bounce radio signals off the ionosphere to receivers over the horizon. Even shorter wavelengths than skywaves diffract and bend even less, and do not bounce off the ionosphere, tending to travel on a line of sight [1] and are thus used to send signals within the visible horizon.

Aside from their extensive use in modern technology and communications on Earth, they are extremely useful in Astronomy because they are a type of light that passes through material of the galaxy and universe largely unhindered. For example, while Visible Light might be blocked by a Nebulae, radio waves can pass through without being disrupted too greatly, giving us information on what is on the other side which otherwise would not be visible.

Discovery of Radio Waves

Radio waves are an electromagnetic phenomenon — they have properties of electric and magnetic fields and waves, like all light — and were first predicted in the James Clerk Maxwell’s theory of electromagnetism in 1867.

Maxwell predicted that entwined electric field and magnetic field could propagate through space as an electromagnetic wave, and further postulated that light itself was just such an electromagnetic wave. This was the first time that we understood exactly what light is. These predictions were the result of his mathematical theory that we call Maxwell’s equations.

Heinrich Hertz, a German physicist, was able to experimentally prove the existence of these electromagnetic waves in 1887, about twenty years after they were proposed by Maxwell. In his laboratory he generated radio waves (with very long wavelengths compared to visible light) which nonetheless had the same properties: standing waves, refraction, diffraction, and polarization.

Generation, Reception, and Application

[Full Article: Generation and Reception of Radio Waves]

Radio waves can be generated in both artificial and natural situations, whenever a charged particle undergoes an acceleration of some kind. Whenever a charged particle accelerates (increases velocity in a positive acceleration or decreases velocity in an arbitrarily negative acceleration) a radio wave of a specific frequency is emitted.

Notes

Resources

1. “Radio Waves”. Wikipedia. <https://en.wikipedia.org/wiki/Radio_wave>. Accessed 04 Nov 2024.

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