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Long-haul . Communication None of the circuits that we have so far discussed are suitable as they stand for long haul communication. To get us anywhere with long haulwe need to address ourselves to the following inescapably pertinent topics: | Networks and Telecommunications Design and Operation Second Edition. Martin P. Clark Copyright 1991 1997 John Wiley Sons Ltd ISBNs 0-471-97346-7 Hardback 0-470-84158-3 Electronic 3 Long-haul Communication None of the circuits that we have so far discussed are suitable as they stand for long haul communication. To get us anywhere with long haul we need to address ourselves to the following inescapably pertinent topics attenuation loss of signal strength over distance line loading a way of reducing attenuation on medium length links amplification how to boost signals on long haul links equalization how to correct tonal distortion multiplexing how to increase the number of circuits that may be obtained from one physical cable In this chapter we discuss predominantly how these line issues affect analogue transmission systems and how they may be countered. The effects on digital transmission are discussed in later chapters. ATTENUATION AND REPEATERS Sound waves diminish the further they travel and electrical signals become weaker as they pass along electromagnetic transmission lines. With electrical signals the attenuation as this type of loss in signal strength is called is caused by the various electrical properties of the line itself. These properties are known as the resistance the capacitance the leakance and the inductance. The attenuation becomes more severe as the line gets longer. On very long haul links the received signals become so weak as to be imperceptible and something needs to be done about it. Usually the attenuation in analogue transmission lines is countered by devices called repeaters which are located at intervals along the line their function being to restore the signal to its original wave shape and strength. 29 30 LONG-HAUL COMMUNICATION Signal attenuation occurs in simple wireline systems in radio and in optical fibre systems. The effect of attenuation on a line follows the function shown in Figure where the signal amplitude the .