Data reception

Chapter Data reception

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • 27CHAPTERData receptionONCE A SIGNAL HAS LEFT A TRANSMITTER, THE IMPULSES TRAVEL, ORpropagate, in a cable, optical fiber, or space. In cables, the signals are ac (usually) or dc (sometimes). In fiberoptic systems, thesignals are infrared or visible light. The signals are confined in cables and fibers; theonly important variable is the attenuation per kilometer. This depends on the ac fre-quency, the thickness of wire, or the clarity of optical fiber material.In communication via electromagnetic waves, the propagation is affected by sev-eral factors.Radio wave propagationHere is a summary of the main things that affect EM wave communications.PolarizationThe orientation of the E flux is the polarization of an EM wave. If the E flux lines areparallel to the earth’s surface, you have horizontal polarization. If the E flux lines areperpendicular to the surface, you have vertical polarization. Polarization can beslanted at any angle between horizontal and vertical.The orientation of the E flux lines sometimes rotates as the wave travels throughspace. This is circular polarization if the E-field intensity remains constant. If theE-field intensity is more intense in some planes than in others, the polarization is saidto be elliptical. Rotating polarization can be either clockwise or counterclockwise,viewed as the wavefronts approach you. This is the sense of polarization.The line-of-sight waveElectromagnetic waves follow straight lines unless something makes them bend.Line-of-sight propagation can take place even when the receiving antenna can’t be seen499Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.