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Chapter 5:
The Spectrum and Its Uses
Satellite telecommunication - and much other terrestrial telecommunication - uses radio waves to carry the information from source to destination. It is necessary, therefore, to understand their basic properties and the limitations on how these waves are generated, transmitted, and received. Radio is just the lowest-frequency part of a phenomenon called electromagnetic waves. They are so-called because they are oscillating waves of electrical and magnetic fields traveling through space, and sometimes through other materials. One analogy is the waves produced on a string by shaking one end of it. Transmission through space is called radiation. (This should not be confused with the radiation caused by atomic and nuclear processes.) The electromagnetic spectrum is the range of these waves, and is literally infinite. But because different waves behave differently and require differing technologies for their use, only certain parts of this spectrum are useful for communication. You have been exposed to such waves all your life, for they include visible light, the x rays used by your dentist, the infrared lamps that keep your food warm in restaurants, the ultraviolet rays that give you a suntan or burn, the microwaves that cook your popcorn, and the waves that bring you radio and television. As we have seen in Chapter 2, competition for spectrum is fierce.
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