Wireless and personal communications systems

Chapter Wireless and personal communications systems

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • 32CHAPTERWireless and personalcommunications systemsTHE TERM WIRELESS WAS COINED IN THE LATE NINETEENTH CENTURY WHENinventors toyed with the idea of sending and receiving telegraph messages using elec-tromagnetic fields rather than electric currents. In the early twentieth century, thetechnology became known as radio; video and data broadcasting and communicationswere added in the middle of the century and the general term electromagnetic com-munications emerged. The word wireless was relegated to history.In the late 1980s, the term found new life. Today it refers to communications, net-working, control devices, and security systems in which signals travel without directelectrical connections.Cellular communicationsRadio transceivers can be used as telephones in a specialized communications sys-tem called cellular. Originally, the cellular communications network was patchy andunreliable, and was used mainly by traveling business people. Nowadays, cellulartelephone units are so common that many people regard them as necessities.How cellular systems workA cellular telephone set, or cell phone, looks and functions like a cross between acordless telephone receiver and a walkie-talkie. The unit contains a radio transmit-ter and receiver combination called a transceiver. Transmission and reception takeplace on different frequencies, so you can talk and listen at the same time. This ca-pability, which allows you to hear the other person interrupt you if he or she chooses,is known as full duplex.606Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.