The operation of the radio is based on the transmission and reception of electromagnetic waves. Its history goes back to the late nineteenth century, when Heinrich Hertz invented the oscillator, a device that produced and received waves of this type. Later, this device was perfected by the Italian Augusto Righi. Branly French continued this research and in 1890 created the coherer, which allowed to transform these electromagnetic waves into electrical impulses. Finally, in 1895, the Italian Guglielmo Marconi succeeded in transmitting signals from a distance.
A radio system consists of several stages: the transmission, in which the transmitter generates current and charge transferred to the antenna to radiate, the modulation of these vibrations before reaching the antenna, the antenna radiation and reception of vibrations by a receiver. Hertz pioneer name served to designate the magnitude of cycles per second, with which electromagnetic waves are measured. A kilohertz (kHz) equals 1,000 cycles per second, and one megahertz (MHz) to 1 million cycles per second.
VHF is a very high frequency band between 30 and 300 MHz, and is used for television broadcasts, amateur radio and FM broadcasts.
The carrier wave is modulated by varying the frequency, which shall be known as FM (frequency modulation). Shows signs of interference and noise free, and takes place in high frequency bands of 88-108 MHz
The carrier wave can be modulated by changing the amplitude of the wave, and which is known as AM (amplitude modulation). It is used in radio broadcasting and telephony carrier wave, among other services.