The practical telephone handbook and guide to the telephonic exchange (1906) (14569736577)

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:

ring operations are the same as in the last case. Both-Way Junctions.—Where only one junction line is pro-vided between two exchanges, or where it is considered ofadvantage to be able to work the junction lines provided,in both directions, it is necessary to have automatic signallingand clearing arrangements at each end, so as to work the linesto the utmost efficiency. 252 PRACTICAL TELEPHONE HANDBOOK Equifotential System.—This is probably the simplest of thevarious arrangements for working both-way junctions, andis shown in Fig. 264. It will be seen that 7-point break-jacks are used at each end of the line, and that in the normalcondition two equal batteries are connected to the line throughtwo double-wound 100-ohm indicators, so as to be in oppositionand neutralise each other, so that no current passes. Whena plug is inserted at, say, the A exchange end, the batteryat that end is cut off, and the battery at the B end becomesoperative. Current passes through the two halves of the

Text Appearing After Image:

Fig. 263.—Ringing Junction between Magneto Excl langes indicator, through both lines, the two halves of the double-wound retardation coil at the A exchange, the grid in-dicator, and. to earth through the extra spring and contactof the jack. The operator at the B exchange beingcalled by the falling of the 100-ohm indicator, plugs in, thuscutting off the battery, receives the instruction, and connectsthe wanted subscriber. Clearing.—The ordinary clearing signals are provided inthe operators cord circuits at the two exchanges. Anoperator, on taking out the plug at one end, causes the actuationof the grid indicator at the other <jnd by the current from the JUNCTION-LINE WORKING 253 battery at the far end, which remains connected until the lineis cleared. The calling indicators should be of some self-restoring pattern, as they are actuated when a plug is with-drawn at the same end, and would, therefore, give troubleby needing restoration when the line was cleared. The arrangement sh

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1906

Northeastern University, Snell Library

http://commons.wikimedia.org/

public domain