Radio waves
From Wikipedia, the free encyclopedia
Radio waves are a kind of electromagnetic wave in the radio frequency portion of the electromagnetic spectrum. Their most common use is to transport information across distances without wires. Radio waves are distinguished from other kinds of electromagnetic waves by their wavelength. The wavelength for radio waves is considered to be between around 50,000 km and a few mm. A related factor that distinguishes radio waves from other kinds of electromagnetic waves is that their wavelength is amenable to being generated and detected by electronic means. Antenna dimensions generally need to be comparable to the wavelength of the wave to work efficiently. Longer waves are not very practical because of the enormous antennas needed to produce them, although they are sometimes randomly produced by lightning. Since shorter electromagnetic waves are typically produced by molecular, atomic or subatomic phenomonia, they are not usually considered radio waves. Radio waves are also produced by cosmic phenomonia in deep space. Radio waves are typically produced by causing radio frequency alternating electric current to flow in antenna wires. Radio waves are received by placing an antenna wire in the electromagnetic field of the waves and electronically detecting the signal that the field induces in the antenna wire. Information is transported via these radio waves, by converting the content or data to be sent, into electrical signals and using them to modulate the transmitted waves. The receiver receiving the radio waves then demodulates the signal from the antenna and converts it back to recover the original information. In this way radio waves are used to transfer a wide variety of information classes including voice, music, sound, television pictures, technical data and digital network information.
