04-11-2016, 11:46 AM
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Introduction:
Radio waves are electromagnetic waves of long wavelength compared to other wavelengths. They are at the end of the electromagnetic spectrum. They travel at the speed of light in the Earth's atmosphere that is almost instantly on a human scale. It is a widely used wave as it requires simple, inexpensive devices. In what areas do we use radio waves? How to propagate radio waves?
I -1- short history of the discovery of radio waves:
FM radio is a technology diffusion "radio" sound that uses frequency modulation (FM or Frequency Modulation) radio waves. FM radio stations transmit on the frequencies of 88-108 MHz. January 5, 1940, a demonstration of the FM radio to the FCC (Federal Communications Commission of the US) was performed for the first time. On 1 March 1945, W47NV began broadcasting in Nashville (Tennessee), becoming the first FM radio station. Emissions can be "mono" or "stereo", in which case the tracks "right" and "left" are multiplexed (mixed) into a single signal that is received either by monophonic receivers as stereo equipped with a decoder separating the two original channels. The receiver can switch to stereo or mono depending on the quality of signal reception. However, some stations broadcast exclusively in mono. An additional 57 kHz signal can transmit digital information (RDS, Radio Data System): among others, the name of the station, neighboring frequencies to track the frequency changes during a trip, etc. The term "FM" is a misnomer, since the frequency modulation (FM) may be performed on any frequency therefore in any frequency band. This term originates from the fact that the only FM radio had VHF Band II (87.5 to 108 MHz), and thus this frequency range is now called, inappropriately, "FM ".
Radio waves were the first domain electromagnetic wave frequency to be used to communicate. Since then, other areas are used but are superimposed on them without replacing them.
I-2-Electromagnetic waves:
An electromagnetic wave has both an electric field and a magnetic field oscillating at the same frequency. These two fields are perpendicular with respect to each other are propagated in a medium in a direction orthogonal (figure below).