Electrical current

OK. So we have a signal that is sent to a radiosmitter's antenna. How does that signal get from the antenna to the air?

Let's first take a look at the signal. The signal is an electic current, and every electric current is actually electrons moving in a wire.

Wire is made of metal, usually copper. All of the atoms that make up the wire have something in common -- each has one or two electrons in its outer-most shell.

These electrons do not have a strong bond with the rest of the atom. In fact, it takes just a slight amount of energy to push the electron away from its atom.

But if you have enough energy, the outer electrons from all of the atoms will move at once. They will each travel from one atom to the next atom, and so on.

Electromagnetic field

Back to our radio signal. The electrons in our wire are moving, but not in one direction. These electrons are moving back and forth.

Actually, the wave displayed in the activity is a representation of the back and forth movement of electrons. If the wave has a frequency of 200,000 Hz (cycles per second), the electrons in the wire are moving back and forth 200,000 times a second.

When electrons move in a wire, an electromagnetic field is created around that wire. There's no magic behind this; it's just the way things work.

At the antenna

Just as the electrons move in the wire, they move in the transmitter's antenna. And just as an electromagnetic field is created around the wire, a field is created around the antenna.

But there is a difference between the wire and the antenna. The wire is shielded (surrounded by another wire) to keep the electromagnetic field in. The antenna, on the other hand, is designed to radiate the electromagnetic field.

The electromagnetic field travels from the antenna in all directions and at the speed of light. It travels until it hits your radio's antenna as well as hundreds of other receiving antennas.

And what happens at the receiving antenna? Just as a current in a wire produces an electromagnetic field, an electromagnetic field produces current in a wire (or antenna). This current is then amplified and processed by the radio.