1.1.1 Electromagnetic Waves Can Carry Information

During the twentieth century, technological development has been dominated by the use of radio waves for transporting signals over very long distances. This development is directly correlated to the property of electromagnetic (EM) waves to be propagated with no absorption in a vacuum, and with very low absorption in the atmosphere.

An electromagnetic wave gives some information about the source from which it has been emitted, often this information is not elaborated on at all. typically: the source is ON, or the source is OFF. Astronomical observation is very enlightening as an important indication of this; it just indicates that a star exists in a given direction and has emitted light having a certain color.

Engineers have been creative and have elaborated devices able to permanently emit electromagnetic waves, with well-controlled amplitudes and/or frequencies: it is said that a carrier wave has been produced, some of its characteristics being modulated. These same engineers have imagined and achieved devices able to receive the wave and to extract from it, this is said to detect the signal of modulation.

An electromagnetic wave is thus able to carry over great distances the information that is represented by the modulating signal. If, for this modulation, one uses the signal of a microphone in front of which an orator is speaking, it is seen that the speech can be broadcast. After reception, detection, and, eventually, amplification