Thursday, April 12, 2007

Radio

In class I mentioned a little bit about radio waves. Here I will mention a little bit more.

If you could see all the radio waves around you, you would literally be blinded: not only are there all the radio signals coming from all the different TV and radio signals, there are also radio waves transmitted by the police, the army, the civil defence, the air force, commercial flights, GPS signals and much much more.

Each of these signals are the form of a typical transverse wave. The information is encoded in two ways: AM or FM. AM stands for amplitude modulation, which basically means the different information is encoded in the varying amplitudes of the wave. FM, frequency modulation, means that the changing frequencies of the wave can be interpreted and translated into real pieces of information.

A radio set typically consists of two things: a transmitter, and a receiver. Their names should tell you what they do: a transmitter takes some information, let's say something that is being said in the form of a sound wave, and turns it into a radio wave (either FM or AM). A receiver does the exact opposite. Both of these things make use of antennae to transmit or receive the info.

A transmitter is pretty easy to imagine: basically you do what would be the equivalent of turning a switch on and off again and again to produce an electric current wave. This electrical wave is then sent to an antenna, which is essentially just a straight wire, where the current moving in this antenna will be converted into radio waves.

Of course the electric current wave will have either its amplitude or its frequency changed over the course of time, which encodes information in the wave. So, when I receive the wave, the radio can produce the sound of music or some kind of information by observing the changes in amplitude or frequencies over time.

When radio waves arrive at an antenna, it will cause an electric current to flow within the antenna. This current will then flow to the receiver. There are thousands of radio waves arriving at the antenna, but the receiver can be adjusted electronically to filter all but one frequency. How? You can read up about the concept: it's known as resonance, which is also the process by which a singer is able to break a crystal glass, although in a very different way.

The current that is filtered through is then passed through a demodulator, a series of complicated electrical components that will break up what is encoded in the wave and then sends the appropriate electrical signals to the speakers. Along the way, the signals are amplified, so that we can hear the signal clearly.

This is of course much too simplistic. For more information, you can check out howstuffworks: http://electronics.howstuffworks.com/radio.htm, which gives a good explanation of radio, and a good explanation of many other things that you can check out for yourself.

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