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How to View the Spectrum: To see a part of the human generated EM spectrum click on the picture above.The Spectrum runs from 175 MHz to 3 GHz and is updated every 6 seconds. It shuts off after a few minute but can be restarted as many times as you would like.
To view the spectrum you must have Java enabled in your browser and have a Java runtime environment installed on your computer. These are available for free by clicking here.
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Each part of the EM spectrum is like a wave—with a unique wavelength—moving outward from a pebble tossed in a pond. (Wavelength is the distance between peaks.)
Light’s wavelengths go from about 4x10-7meters for violet to 7x10-7 meters for red light—about 200 times shorter than the width of a human hair. What our eyes detect is only tiny portion of the vast EM spectrum. The unseen part is like a hidden world with all sorts of invisible activity, much of which profoundly affects on our lives.
Amazingly, EM waves can transmit energy without transmitting matter. In fact, unlike the waves in a pond, which are mechanical waves and need water to exist, EM waves need no matter of any kind. They bring us energy from the Sun through the vacuum of outer space, warming our world in the process. They also bring us all kinds of information and communications.
The EM Spectrum Generated by Humans
The screen at right reveals a segment of the unseen spectrum being detected right now by an antenna atop Roper Mountain at the science center in Greenville SC. This segment shows wavelengths from 10 to 600 cm and is of particular value for carrying human communications. Each spike represents a different human communication. (To check out the visible light conditions at Roper Mountain, click here.)
The height of the spike represents the strength of the signal. High continuous spikes generally indicate TV or radio stations that are continuously broadcasting. TV and radio stations must have strong signals, hence, high spikes, so that they can travel long distances. In contrast, cell phone and WIFI signals are weak and intermittent since they are only used as needed and typically travel much shorter distances.
The EM Spectrum as a Limited Natural Resource
Unfortunately, waves carrying communications interfere with each other if their wavelengths are similar in size. Since available spectrum is a limited natural resource, the government has designated how each section can be used. It’s illegal to temporarily communicate on an unauthorized section even if it becomes available. However, as you can see, many parts of the spectrum regularly go unused, Making better use of these parts could dramatically increase the amount of communication the spectrum can handle.
In the early days of wireless communication, there was more than enough spectrum to handle all the means of using it. Now, with new devices like cell phone and WIFI, the demand for available spectrum has exploded. The Center for Research in Wireless Communication at Clemson University, primary sponsor of this display, is dedicated to helping meet this demand by maximizing the use and availability of the electromagnetic spectrum.
Human Wireless Communication
Much of the EM spectrum with wavelengths longer than visible light is used for human communications. For example, infrared is used for TV remote controls, microwaves for cell phones, radio waves for (you guessed it) radio, etc.
Waves in this section of the spectrum are not considered ionizing and at low levels of intensity they're not considered harmful. However, at high levels such as those found in microwave ovens, they can cause burns. The extremely high levels of infrared given off by nuclear bomb blasts can actually vaporize objects including people. |
