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Radio is a communication system using electromagnetic waves that propagate through space.
Radio waves of different length (wavelength) are used for different purposes.
In general the electromagnetic waves are distinguished by their frequency that is inverse to the wavelength.
Shorter waves have a higher frequency and a lower wavelength, while the lower frequency waves have a higher wavelength. The frequency corresponds to a specified number of cycles per second. Actually, you know that smartphones used to use radio frequencies? Read it about the cost of smartphones with discount.
It was the name of the German radio pioneer Heinrich Hertz that served to baptize the frequency unit of measurement; Hertz (Hz).
Thus one cycle per second equals 1Hz (Hertz), 1KHz equals 1000 Hz, or 1000 cycles per second, and so on. Radio waves range from a few KHz (Kilohertz) to several gigahertz (GHz), 1,000 million cycles per second.
Visible light waves are much shorter. In space, electromagnetic radiation propagates in the form of waves at a uniform velocity of almost 300,000 km per second.
Radio waves are used not only in radio broadcast but also in wireless telegraphy, telephones, television, radar, navigation systems and space communication. In the atmosphere, the air's physical characteristics give rise to small variations in the wave motion that cause communications errors, such as radar.
In addition, storms and electrical disturbances cause abnormal phenomena in the propagation of radio waves.
The electromagnetic waves in a uniform atmosphere propagate in a straight line and as the terrestrial surface is practically spherical the communication at great distance is possible thanks to the reflection of the radio waves in the ionosphere. Radio waves with a wavelength shorter than 10m, which are called very high (VHF), ultra high (UHF) and super high (SHF) frequencies, are not reflected in the ionosphere. Thus, in practice, these very short waves are only captured by the visual distance.