If we go back to the times when mail was the only method to transmit information, we will realize the importance of telecommunications: staying together in the distance is something that goes beyond the sentimental. The development of science and society depends on the dialogue of many people and the transmission of ideas.
If the information is not transmitted fluently, the development is delayed and the evolution stagnates. This is already sufficient justification for the property that in our society is given to telecommunications and the efforts that are devoted to its development. Its start we owe to a physicist named Hertz. He was the first to experiment with a new concept that led to the development of modern communication at a distance and then we discover: electromagnetic waves.
We must remember that charged particles create an electric field around them and, depending on the circumstances, a magnetic field. From now on to the union of both we will call it electromagnetic field.
The next thing we will do is to consider how qualitatively affects the movement of charges to the field. We saw that the field took in each point of the space a value that depended on the distance of the load to the point. If the load moves, the distance of the load to any point will be affected and, therefore, the value of the field will vary.
How will the field vary? The possibilities that we have are two: the change of position of the load could cause the value of the field in all the space automatically, or the change could take a certain time to take effect. Experimentally it is verified that the correct option is the second one. The change is transmitted at a given speed that turns out to be that of light (300.00 km / s). Thus, a point located 300,000 km from the load will take 1 s to perceive the movement of the load; another located at 600,000 km will take 2 s, and so it can be easily calculated for any distance. This is an observable effect for long distances since, for 300 km, the delay will be just one thousandth of a second, and we can practically disregard it. It can be verified that the variation in the electromagnetic field is transmitted just like a wave that moves at the speed of light. We will call, then, electromagnetic waves to the transmission of the variation of the field, and we will say that the movement of the charges causes electromagnetic waves that move at the speed of light.
The fact that the speed of these waves is that of light is not a coincidence; in fact, light is nothing more than an electromagnetic wave. The microwaves, the X-rays, the ultraviolet, they are all electromagnetic waves. The only difference between them is the wavelength, already explained in the topic dedicated to waves, which gives them different properties according to their value. To study the way these waves are used in telecommunications, we focus on the use that is given to them in the two most widespread media: radio and television.
If we grab a stretched paper and talk in front of it we can see that it vibrates. The microphone uses this same principle: when we speak in front of one, we vibrate a membrane that transforms its vibrations into an electric current. The current thus generated, in some way, encoded the information of our voice along with what we said. This current causes in the antenna of the transmitter a movement of charges that produces electromagnetic waves, as we discussed previously.