The carrier frequency f is modulated by the signal containing the information we wish to transmit in space using the propagation properties of the carrier wave. Thus we find the kilohertz (kHZ), the megahertz (MHz) and the gigahertz (GHz). In radio electricity, as the period T is much shorter than one second, frequencies are expressed as multiple of the hertz.
The associated frequency f is none other than the inverse of period T, and is expressed in hertz (Hz). This is a periodic signal of sinusoidal shape and of period T.
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The radio wave is produced by a generator delivering voltage and a current of great amplitude. Generation and propagation of radio waves 2.1 Basic configuration of a radiation sourceĤ Figure 1 shows very schematically the structure of a radiation source producing electromagnetic waves for wireless transmission. Some information regarding electromagnetic pollution are provided at the end of the article. In the conclusion, we reflect on the environmental impact of antennas and on their future deployment following the adoption of digital modulation techniques. We conclude this section with selected information on extraterrestrial radio waves. In the third section, we discuss the role of soil electrical conductivity as well as the effect of obstacles.
In the second section, we discuss wave dispersion, transmitter antennas and radiation directivity. the description of their physical properties such as frequency and wavelength as well as that of the electrical and magnetic fields. For the sake of accessibility, we will limit ourselves to providing a brief description of certain fundamental properties and an examination of relevant examples.ģ In the first section, we review the basic properties of radio waves i.e.
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Depending on the parameters of interest, an electromagnetic wave can be considered a vibration or a flux of photons traveling in free space at the speed of light.Ģ The rigorous study of the distribution of radio waves in space requires advanced mathematical formulations that are beyond the scope of this paper. Now more often referred to, in the light of recent applications, as “radio waves” or “Hertzian waves”, the fields propagated by these waves manifest themselves by inducing voltage or currents on any electrical conductor exposed to these phenomena. However, one had to wait until the very end of the 19 th century for the German physicist Heinrich Hertz to provide, in 1888, experimental proof showing that electromagnetic fields propagate through space at the speed of light in the region of 300,000 km/s. From a historical perspective, the existence of electromagnetic waves was proven around 1864 with the theoretical work of British physicist James Clerk Maxwell. 1 The electromagnetic waves discussed here apply to radio broadcasting, television and wireless transmissions used in mobile technology.
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