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Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Naturally-occurring radio waves are produced by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves may cover a part of the Earth very consistently, shorter waves can reflect off the ionosphere and travel around the world, and much shorter wavelengths bend or reflect very little and travel on a line of sight.

Diagram of the electric (E) and magnetic (H) fields of Radio Waves emanating from a grounded radio transmitting antenna (small dark vertical line in the center). The E and H fields are perpendicular as implied by the phase diagram in the lower right.

Contents

Discovery and utilization

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves.

Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. He then proposed equations, that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887, Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical the use of radio waves to transfer information through space.

Propagation

The study of electromagnetic phenomena such as reflection, refraction, polarization, diffraction and absorption is of critical importance in the study of how radio waves move in free space and over the surface of the Earth. Different frequencies experience different combinations of these phenomena in the Earth's atmosphere, making certain radio bands more useful for specific purposes than others.

Radio communication

In order to receive radio signals, for instance from AM/FM radio stations, a radio antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune in to a particular frequency (or frequency range).[1] This is typically done via a resonator (in its simplest form, a circuit with a capacitor and an inductor). The resonator is configured to resonate at a particular frequency (or frequency band), thus amplifying sine waves at that radio frequency, while ignoring other sine waves. Usually, either the inductor or the capacitor of the resonator is adjustable, allowing the user to change the frequency at which it resonates.[2]

Special properties of RF electrical signals

Electrical currents that oscillate at RF have special properties not shared by direct current signals. One such property is the ease with which they can ionize air to create a conductive path through air. This property is exploited by 'high frequency' units used in electric arc welding, although strictly speaking these machines do not typically employ frequencies within the HF band. Another special property is an electromagnetic force that drives the RF current to the surface of conductors, known as the skin effect. Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor. The degree of effect of these properties depends on the frequency of the signals.

In medicine

Radio frequency (RF) energy has been used in medical treatments for over 75 years[3] generally for minimally invasive surgeries and coagulation, including the treatment of sleep apnea.[4]

See also

References

  1. ^ Brain, Marshall (2000-12-07). "How Radio Works". HowStuffWorks.com. http://electronics.howstuffworks.com/radio8.htm. Retrieved 2009-09-11. 
  2. ^ Brain, Marshall (2000-12-08). "How Oscillators Work". HowStuffWorks.com. http://electronics.howstuffworks.com/oscillator3.htm. Retrieved 2009-09-11. 
  3. ^ Ruey J. Sung and Michael R. Lauer (2000). Fundamental approaches to the management of cardiac arrhythmias. Springer. p. 153. ISBN 9780792365594. http://books.google.com/books?id=S1fWhl2c5zIC&pg=PA153&dq=rf+coagulation+75-years&lr=&as_brr=3&ei=IIhuSpfBJ6aqlQT-n7nmDg. 
  4. ^ Melvin A. Shiffman, Sid J. Mirrafati, Samuel M. Lam and Chelso G. Cueteaux (2007). Simplified Facial Rejuvenation. Springer. p. 157. ISBN 9783540710967. http://books.google.com/books?id=w1fQK21WK28C&pg=RA1-PA157&dq=rf+coagulation+sleep-apnea&lr=&as_brr=3&ei=ZYduSumzKJCckgT_-bHdDg. 
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Radio Wave may refer to:


Simple English

Radio waves make up part of the electromagnetic spectrum. These waves are packets of energy with differing wavelengths, similar to visible light waves, X-rays or Gamma rays, except longer.

A Radio wave, like other electromagnetic waves, is similar to an ocean wave or any other type of wave. Both types of wave have a hill and valley shape, repeating over and over. A wavelength is measured as the distance from the top of one crest to the top of its neighboring crest. While the wavelength of visible light is very very small, less than one micrometer and much less than the thickness of a human hair, radio waves can have a wavelength from a couple centimeters to several meters. Antennas designed to detect radio waves are usually similar in size to the wavelength they wish to detect. This is why many radio antennas (like those on cars) must be very long. If the antennas are not close to the size of the wavelength they do not usually do a good job of detecting the waves.

Manmade radio waves have been used for a long time to send information, receive information, and to 'see' objects. Radar uses radio waves to 'see' distant objects by bouncing waves off an object and seeing how long it takes for the waves to return. Radar can even be used to find oil or see what chemicals are in soil. Radios also use these waves to send and receive information. Natural radio waves were first discovered in the 1930's by a man named Jansky, working for Bell Laboratories. Before his discovery, everyone thought only people could generate radio waves. Bell was detecting static on his radio channels, and had Jansky try to figure out where this static, or interference was coming from. Surprisingly, the interference was coming from space! This discovery eventually led astronomers to look at radio waves along with optical waves to find things in the sky. These radio astronomers use giant Radio telescopes, shaped like satellite dishes, to gather and analyze the waves.

Radio waves are used for many things today. They broadcast TV, communicate with satellites, let cell phones communicate with each other, make radar systems, and allow computers to share information without wires.


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