Electromagnetic Spectrum (Linktionary term)

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Electromagnetic Spectrum

Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Energy is transmitted in three ways: electromagnetic radiation, conduction, and convection (heat transfer). Because electromagnetic waves do not necessarily need a material medium for transmission, they are used for a wide range of communication, including communication over copper and fiber-optic cable, as well as through water, air, and the vacuum of space.

Electron movement causes electromagnetic radiation. The frequency is the number of oscillations per second of the resulting wave, also called Hz (hertz). The wavelength is the distance between crests in the wave. The higher the frequency, the shorter the wavelength. As outlined in Figure E-2, the length of a wave may be larger than the earth's diameter and smaller than an electron.

ANCHOR HERE: Figure 2 (see book)

Wireless systems use specific bands in the radio, microwave, and infrared range, as shown in Figure E-2. The spectrum is allocated by governments and international organizations. In the United States, the FCC allocates the spectrum and sells it at auctions to companies that want to operate communication services in designated markets. Spectrum allocation is designed to prevent overlapping signals and interference. In fact, interference still occurs. Devices like microwave ovens, wireless LANs, and cellular phones operate in the same frequency. Some common frequency allocations are listed in the following table.

Note that this topic continues in "The Encyclopedia of Networking and Telecommunications."

Cordless telephones	46 to 49 MHz
Mobile radio (not telephone) services	30 to 300 MHz
Wireless local loop	420 to 450 MHz
Citizens band radio	462 to 467 MHz
UHF TV channels 60-69 (may be allocated to cellular)	747 to 762 MHz 777 to 792 MHz
Cellular services	824 to 849 MHz 869 to 894 MHz
Cellular services, GSM	890 to 914 MHz 935 to 959 MHz
Mobile satellite service and GPS (Global Positioning System)	1.2 to 1.3 GHz
3G bands (potential areas of use)	Other Cellular ranges 1.7 to 1.8 GHz Some MMDS 2-GHz ranges
Cellular PCS (personal communication system)	1.85 to 1.91 GHz (licensed) 1.93 to 1.99 GHZ (licensed) 1.91 to 1.93 GHz (unlicensed)
High-speed unlicensed wireless LANs (IEEE 802.11b), home networking (e.g., Home RF), Bluetooth PAN (personal area network), cordless phones, and consumer electronics	2.4-GHz band
U-NII (Unlicensed National Information Infrastructure). IEEE 802.11a wireless LANs operate in this range.	5.15 to 5.35 GHz 5.725 to 5.825 GHz
MMDS (Multichannel Multipoint Distribution Service) fixed broadband wireless for local access (48 km/30 mi)	2.5 to 2.7 GHz 3.4 to 3.7 GHz
LMDS (Local Multipoint Distribution Services) fixed broadband wireless for local access (8 km/5 mi)	10 to 43 GHz (various bands)
Optical wireless, e.g., Terabeam's freespace laser system (no licensing required)	190 THz (infrared range)