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Assignment 1-Cont. - 14103_12

Fire Controlman Volume 06-Digital Communications
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CHAPTER  1 FUNDAMENTALS OF DATA COMMUNICATIONS INTRODUCTION Although  you,  as  a  Fire  Controlman,  may  not  be  directly  involved  in  data communications,  you  definitely  need  to  be  aware  of  how  data  communications affects your ship’s mission. This  training  manual  introduces  and  explains  the basics  of  data  communications.  Computer  data  frequently  must  be  transmitted  from one point to another. The distance involved maybe a few feet, or it may be hundreds of  miles.  Data  transited  over  long  distances  often  must  be  converted  to  a  form compatible  with  either  landline  or  radio  wave  transmission  and  reception.  This chapter  explains  how  such  conversion  occurs  and  techniques  used  in  the  conversion and transmission procedures. After completing this chapter, you should be able to: State the types of communications systems. Describe the decibel system of power measurement. Explain  asynchronous  and  synchronous  communications  as  used  in  data communications systems. Describe  the  methods  of  data  modulation  and  demodulation  used  in various types of data networks. Describe   the   operation   of   modems   used   in   data   communications networks. Describe  the  methods  of  multiplexing  data  in  communications  networks. COMMUNICATIONS  SYSTEMS The devices used to transfer digital data makeup what  is  known  as  a  communications  system.  In  its most basic form, a communications system consists of the three components shown in figure 1-1. They are Figure  1-1.—Communications  system. the transmitter, the receiver, and a communications channel that connects the two units. The transmitting equipment converts the data of the sending system into a form that can be sent over the   communications   channel,   accepted   by   the receiving equipment, and converted back into usable data  by  the  receiving  system. Data  sent  over  a communications system is in one of the following two forms:  analog  or  digital. An  analog  signal  used  in  data  communications varies  continuously  between  a  minimum  and  a maximum value. As the signal varies, it assumes an infinite number of specific values between the two 1-1






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