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What Is a Radio Wave Anyway? > Signal Speed - Pg. 151

Chapter | 7 Radio/Wireless 151 open space introduces another kind of invisible field that can also influence external objects. Now if you combine these two types of fields into a self-supporting entity, you would have an electromagnetic field or radio wave . We create a radio sig- nal with the circuits in a transmitter, but it is the magic of a device called an antenna that produces the combined electric and magnetic field that we refer to as a radio wave. In the 19th century, a British scientist named James Clerk Maxwell figured out that if you generate a changing electric field, it would, in turn, generate a magnetic field. If the magnetic field is changing and moving forward, it will generate an electric field. The two fields support or regenerate one another as they change and move outward from the antenna that produces them. Maxwell expressed his theories in his famous mathematical equations that form the foundation of radio and light transmission. Trying to draw a picture of a radio wave is somewhat like trying to draw a picture of the wind. Nevertheless, Figure 7.3A is an attempt. Try to think in three dimensions. Current flow in the antenna wire creates the magnetic field lines. The voltage across the two segments of the antenna produces the electric field lines. The picture is somewhat simplified if we just show the field lines as in Figure 7.3B. The electric and magnetic field lines are always at right angles