Communication: How The Radio Spectrum Works

You might understand how your radio works inside, but do you know how it works on the outside? Find out all about radio waves, call letters types of frequencies and how they work to carry and deliver sound.

When you turn on the radio to hear the latest news, weather, or sports, all you probably think about it is tuning in the dial to your favorite station. "Tuning in" means more than just turning the dial, though. When you hear the songs, voices, or other noises that come out of your radio, that means that your radio antenna has received electromagnetic radio signals from the station's antenna. These radio signals have different frequencies. And, radio stations transmit on one specific frequency. That's why your favorite radio station might be 106.1 or 1400, depending on whether it's AM (Amplitude Modulated) or FM (Frequency Modulated). The letters that come in front of the station's frequency, such as WABC, for example, are the radio station's call letters. These letters are set up by the Federal Communications Commission (FCC), and they identify the station. The FCC also gives each station it's specific frequency on which it can transmit its signals on.

If you look closely at the dial on your radio, you'll see that the Frequency Modulated (FM) numbers start at eighty-eight megahertz and end at one hundred and eight megahertz. On the other side of the dial, the Amplitude Modulated (AM) frequencies start at five hundred and thirty five megahertz and stop at seventeen hundred megahertz. The AM and the FM frequencies and their corresponding numbers are all part of what is known as the "Radio Spectrum."

The Radio Spectrum is divided up by frequencies: kilohertz, (kHz), megahertz, (MHz), and gigahertz, (GHz). This chart starts out at the lowest frequencies and graduates to the next higher up, and so on. If you could see the radio spectrum, you would see a red block for VLF (very low frequency); an orange block for LF (low frequency); a yellow block for MF (medium frequency); a light green box for HF (high frequency); a darker green box for VHF (very high frequency; a light blue box for UHF (ultra high frequency); a purple box for SHF (super high frequency); and a rose colored box for extremely high frequency (EHF). Beyond that is a pink box for infrared, and a white box for visible light.



In order to completely understand the Radio Spectrum, you'll need to know what the specific frequencies are. The VLF are ten kHz to thirty kHz; the LF are thirty kHz to three hundred kHz; the MF frequency are three hundred to kHz to three MHz; the HF are three MHz to thirty MHz.

The VHF is subdivided into three groups: thirty MHz to one hundred and forty four MHz, one hundred and forty four MHz to one hundred and seventy four MHz, and one hundred and seventy four MHz to three hundred and twenty eight point six MHz, respectively.

Next comes the UHF frequencies which are also subdivided into six different groups: three hundred and twenty eight point six MHz to four hundred and fifty MHz, four hundred and fifty MHz to four hundred and seventy MHz, four hundred and seventy MHz to eight hundred and six MHz, eight hundred and six MHz to nine hundred and sixty MHz, nine hundred and sixty MHz to two point three GHz, and two point three GHz to two point nine GHz.

The last two frequencies are the SHF, which are two point nine GHz to thirty GHz, and EHF, which are thirty GHZ, and above.

To explain the radio spectrum further, a hertz is a unit of frequency that equals one cycle per second. Its name comes from the German physicist named Heinrich Hertz. Therefore, a kilohertz (kHz), is one thousand hertz. A megahertz (MHz) is one million hertz, and a gigahertz, (GHz), is one thousand million hertz.

There are other electronic devices besides the radio that use frequencies in the radio spectrum too. Besides the amplitude modulated and the frequency modulated radio signals, they include other common devices that you use everyday. Examples include television stations, a garage door opener, cell phones, remote car starters, radio-controlled cars, and police scanners.

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