File:Electrical instruments and telephones of the U.S. Signal corps (1911) (14569889549).jpg

Identifier: electricalinstru00unitrich (find matches)
Title: Electrical instruments and telephones of the U.S. Signal corps
Year: 1911 (1910s)
Authors: United States. Army. Signal Corps
Subjects: Military telegraph -- United States Military telephone -- United States
Publisher: Washington, Govt. print. off.
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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ake andIjreak of the current will cause a series of snappings of the diaphragm,which would completely obscure any talk; if, however, this snappingof the diaphragm is eliminated, talk coming over the line can be heardin the receiver. To do this the rise and fall of the current, due to the 136 ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. opening and closinir of the Morse circuit, must be regulated Avithrespect to the receiver so that no au(Iil)lc indication of it can beheard. This is done by inserting a coil of high self-induction be-tween the telegraph instrument and the telephone. This coil soregulates the ^lorse current with respect to the receiver that wlien thetelephone is joined through a condenser to the line no sound of thetelegrajih instruments can be heard, but telephonic speech coming overthe line will be audible. The condenser, in addition to helping regu-late the ^Nlorse current, prevents the telegraph line from beinggrounded through the telephone. The hardwood box contains a
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Fig. 8!i.—Circuit, common liattery des;k telephone, North type. hand set combinina- the receiver and transmitter, the circuit of thelatter l)eing controlled by a spring switch in the handle. The boxalso contains the calling device, the choke coil, condenser, and thecells of dry battery. The choke coil, whose core consists of a numberof soft-iron Avires projecting a couple of inches beyond the ends, iswound to -1 ohms, so that when the serrated metal ))late is scratchedby the spring controlled by the button on the left the discharge cur-rent Avill be of such volume as to produce a loud note in the receiverat the distant station. AVhen the two stations that ai-e communi-cating with each other aiv l)etween two telegra))h stations one bindingpost on the to^) of each box is connected to the telegraph line and the ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. 137 other grounded. When a telegraph station intervenes between the twotelephone stations the telegraph set must be bridged by a conde

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