Ahhh yes, the radio. Old news right? I mean, this thing has been around for over 100 years. Radio’s have been a part of our lives for as long as we can remember back. We listen to them in our cars, at our office, and in our homes. With the advanced technology available today, the radio is mostly a forgotten luxury. All these years, and we never figured out how the darn radio works! Lets take a more in depth look at the common AM Radio… Ready? Okay, lets go.

AM Radio was the dominant method of broadcasting audio throughout the 20th century, and remains active today. 680 News is still one of my favorite stations that I listen to while driving around. Traffic, weather, and news! It gets the name 680 from the fact that the station is broadcast at a frequency of 680 KiloHertz. But what is a Hertz? 1 Hertz = 1 wave per second. Sound travels through the air in waves. The higher pitched sounds (treble) have higher frequencies. The lower pitched sounds (bass) have lower frequencies. Now we know that frequency is measured in Hertz. So, getting back to my favorite news station 680 News. 680 KiloHertz = 680000 Hertz since 1 KiloHertz = 1000 Hertz. This is just the same as 1000 Milimeters being equal to 1 Meter. Enough about the math already…

AM stands for Amplitude Modulation. I bet you didn’t know that! I probably sound pretty smart, but its just a silly definition. The true test of smarts is how well you can teach a lesson to others. So lets give this a shot. Radio broadcasters such as 680 News send out an electromagnetic signal atop tall buildings via large antennas. The signal travels in all directions for hundreds of KiloMeters. The audible sound range for a human ear is between 20 Hertz - 20000 Hertz. Obviously the 680000 Hertz frequency being sent out by 680 News is too high for our ears to hear. This is strictly a transmission frequency, and is not meant to be heard by anybody directly. So, we need a radio to decipher that high frequency signal and play the sound on a speaker at a lower frequency that we can actually hear. The key here is understanding how Amplitude Modulation works. Amplitude Modulation is the process of mixing lower frequency sound waves with a higher frequency carrier wave. This final frequency is the frequency at which the broadcaster will transmit the signal (680000 Hertz for 680 News). Radios set to the correct frequency can pickup these signals and decipher them. Recall that Amplitude modulation mixes the sound signal with the carrier signal. The Radio in your car will throw away the carrier signal, and send the sound signal to a speaker. The speaker emits a sound when an electrical current passes through an electromagnet which moves the cone in the speaker creating audible sound waves! Whew! I’m glad that lesson is over.

The first AM Radio broadcasts were done in the 1920’s. We’ve been enjoying the radio for years without ever thinking about what goes on behind the scenes. I hope this entry was able to provide some insight, at a basic level, into the science behind the radio. Please comment as to the clarity & coherence of this article, and ask questions at will!

This entry was posted on Sunday, February 1st, 2009 at 1:18 pm and is filed under Advanced. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.