4.1. ORIGIN OF RADIOWAVES

You know that, whenever there is a voltage between two points, an electric field is arising between these two points. You also learnt in Basic Electrical Science that whenever a capacitor is charged, one plate will be positiv and the other negativ. The consequence of these two facts is, that an electrical field, having a direction towards the positivly-charged plate, is build up between the capacitor plates as shown in figure 18 below.

fig. 18

In the same way, the voltage difference between the two wires of an aerial also generates an electric field, which has a pattern and direction that you can see in fig. 19.

fig. 19

Besides this electric field, there is also a magnetic field, which is generated by the aerial current. The plane of this magnetic field is at right angels to the direction of the current flow; and therefore is at right angles to the aerial (see below), the electrical and the magnetic fields are therefor at right angles to each other.

fig. 20

These electrical and magnetic fields alternate about the aerial-building up, reaching a peak, collapsing and building up again in the opposite direction at the same frequency as the aerial current.

In the process of building up and collapsing, a portion of these fields escape from the aerial, and become the electromagnetic waves which radiate through space, conveying the transmitted intelligence to distant receivers.