How Radios Work

Radios are the most common wireless item in existence and are in most homes. We use them for entertainment, communication, as an information source, or even just back ground noise. For many of us radios are almost a necessity, but how much do we know about how they function?

Antennas are one of the key pieces to a radio. Antennas come in a variety of shapes and sizes; they vary from large arrays to a small wire. Much of this variance is based on the broad use of radio waves and practicality; for instance you wouldn't use an antenna from a small radio to send a signal to a satellite.

Antennas work by creating a resonating flow of charge along its element. The resonance is caused by a magnetic field fluctuating through an inductor that is fixed to a capacitor. As a magnetic field fluctuates across a conductor it causes charges to move. This motion causes an electro magnetic wave.

The relations between the electricity and magnetism are explained by Maxwell's equations. Maxwell's equations are four equations that relate magnetic fields electric fields and charges and current.

A radio wave is an electro magnetic wave. We modulate them using three different modulations, frequency modulation, amplitude modulation, and pulse modulation, to carry information.

For frequency modulation slight variances are made in the frequency of the wave to represent different bits of information. This is widely used because it is less likely to have static.

For amplitude modulation the height or amplitude of the wave is changed to contain information. Amplitude modulation is not only used by radio stations but it is also used to send the picture part of television.

Pulse modulation is where there are breaks in the wave to indicate the desired information. This is usually used for morse code but can be used for a few other things as well.

According to maxwell's equations radio waves travel at the speed of light. The magnitude of a wave will decrease at a rate of r^2. Where r is the distance from the origin. This is because the wave is propagates in all directions so the same amount of energy spreads out over a greater area.

But how can we get signals from beyond the horizon? Today we could use satellites, but you can also bounce a radio wave off of parts of the upper atmosphere. This can be done because the sun ionizes levels of upper atmosphere.