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The practical telephone handbook and guide to the telephonic exchange (1906) (14733219826)

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The practical telephone handbook and guide to the telephonic exchange (1906) (14733219826)

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Identifier: practicaltelepho00pool (find matches)
Title: The practical telephone handbook and guide to the telephonic exchange
Year: 1906 (1900s)
Authors: Poole, Joseph
Subjects: Telephone
Publisher: New York, Macmillan Co.
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Boston Library Consortium Member Libraries



Text Appearing Before Image:
in (2), if there is but little friction between the particles of the cord; if there is much of such friction, the amplitude of the waves fall off at the fixed end, as in (3), representing attenuation, which becomes greater the longer the cord. This loss will be less the heavier the cord, the weight giving it greater momentum, LONG-DISTANCE LINES—PUPIN SYSTEM 409 but it will require more force to set it in motion. If a singleweight be attached to the centre of the light cord, the wavewill not travel along it properly, but if this weight be sub-divided, and the parts distributed at equal distances alongthe cord, as in (4), the cord will vibrate like a heavier cord,and waves will be transmitted with but little attenuation. The weights are the equivalent of inductance; the frictionof electrical resistance, and the elasticity of the cord repre-sents the electrical capacity. Practical Application.—A frequency of 750 cycles persecond is usually taken as a standard, as being about midway
Text Appearing After Image:
Fig. 403.—Effect of Loading on Vibrating Cord between the lowest and the highest important frequency ofabout 1500 per second, as shown by Cohen and Shepherd intheir paper read before the I.E.E. on 9th May 1907. It hasalso been found in practice that the attenuation determined byactual speech tests is almost identical with calculated valuesbased upon a frequency of between 750 and 850 cycles persecond. If a line is corrected for this value it will be stillmore nearly correct for less rapid waves. Having fixed upon the amount of attenuation to beallowed for the above frequency, so as to leave a sufficientstrength to ensure good speech, and the amount of inductance 4io PRACTICAL TELEPHONE HANDBOOK to be added to the line per mile, the wave length of the lineis calculated as if the inductance were uniformly distributed,and with the resistance of the coils added to that of the line.For example, take a cable 250 miles long, of 9 ohms per mileresistance, and 074 microfarad capacity per mil

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1906
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Northeastern University, Snell Library
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public domain

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the practical telephone handbook and guide to the telephonic exchange 1906
the practical telephone handbook and guide to the telephonic exchange 1906