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Radio Waves and Radio Spectrum

The Electromagnetic Spectrum_012122A
[The Electromagnetic Spectrum]


- Overview

Radio waves are but one of many waves in the electromagnetic spectrum, which includes other family members like x-rays, gamma rays, infrared rays, and more. These waves can all defy even the toughest physical barriers, transmitting data, video, audio and more through the vacuum of space at the speed of light.

Radio waves are low and medium frequencies and can penetrate walls. Therefore, AM radio can also pick up signals inside buildings. Radio waves are easy to generate and can travel great distances. For these reasons, they are widely used for indoor and outdoor communication.

The diagram above is a great visual for how the electromagnetic spectrum is organized, starting with low frequency and low wavelength on the left. . On this electromagnetic spectrum, you can measure and classify radio waves that are used in Wi-fi, Bluetooth, and other applications in one of two ways:

  • By Frequency. This is the count of how many electromagnetic waves pass through a given point every second, and is measured in Hertz.
  • By Wavelength. This is the distance that you can measure between two of the highest points in a radio wave, which can range anywhere from 100 meters to 1 centimeter depending on the radio wave you’re observing.

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. For example, a radio tuner receives radio waves and converts them to mechanical vibrations in the speaker to create sound waves that can be heard.


- The Radio-Frequency Spectrum

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, 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. 

Within the radio wave family, there are distinct bands separated by both frequency and wavelength which provides some specific channels that devices can be used on.

Both Wi-Fi and Bluetooth share their space in the Ultra high frequency (UHF) band between 300 MHz and 3GHz, along with other gadgets like baby monitors, cell phones, and more. You’ll also find Wi-Fi advancing into the Super high frequency (SHF) band between 3GHz and 30GHz in its most recent evolution. 

It’s because of these separate bands that you can listen to things like your morning AM radio talk show while at the same time browsing the web on your smartphone. Connecting through WiFi on your phone uses the UHF band, whereas AM radio uses the lower frequency bands between 535 kilohertz and 1.7 megahertz.


- Wave Characteristics: Frequency, Wavelength, Amplitude and Wave Speed

Waves cause a disturbance of the medium through which they travel, which allows them to carry energy. The quantity of energy carried relates to the amplitude of the wave. 

The amplitude of a wave is the distance from the centre line (or the still position) to the top of a crest or to the bottom of a trough (i.e., the distance between the top and the bottom of a wave). Amplitude is measured in metres. The greater the amplitude of a wave then the more energy it is carrying. The frequency of a wave is the number of waves passing a point in a certain time. We normally use a time of one second, so this gives frequency the unit hertz, since one hertz is equal to one wave per second. 

Wave speed is measured in metres per second. All the electromagnetic waves travel at 300,000,000 metres per second. Sound travels at about 340 metres per second.


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- Radio Waves and Fields

Understanding any type of radio is impossible without also having a general understanding of the purpose of radio: to send and receive information by using radio waves. Radio waves are just another form of light that travels at the same speed; 186,000 miles per second. Radio waves can get to the Moon and back in 2 ½ seconds or circle the Earth in 1/7 second. 

The energy in a radio wave is partly electric and partly magnetic, appearing as an electric field and a magnetic field wherever the wave travels. (A field is just energy stored in space in one form or another, like a gravitational field that you experience as weight.). These fields make charged particles - such as the electrons in a wire - move in sync with the radio wave. 

These moving electrons are a current, just like in an AC power cord except that they form a radio current that your radio receiver turns into, say, audible speech. This process works in reverse to create radio waves. Transmitters cause electrons to move so that they, in turn, create the radio waves. 

Antennas are just structures in which the electrons move to create and launch radio waves into space. The electrons in an antenna also move in response to radio waves from other antennas. In this way, energy is transferred from moving electrons at one station to radio waves and back to moving electrons at the other station.


- Applications of Radio Waves

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. 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. 

Some of the areas of applications of radio waves are: 

  • Broadcasting and multicasting
  • Fixed and mobile radio communications
  • AM and FM radio
  • Television
  • Marine communication
  • Wireless computer networks
  • Cordless phones


- Animation of A Half-Wave Radio Dipole

Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.


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