File:Bell telephone magazine (1922) (14569933590).jpg

Identifier: belltelephonemag19amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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reeconstants of the line structure, thatis upon its resistance, capacitance andinductance per mile. Capacitance is always present ina telephone line, but inductance maybe negligible, as it is in cable, wherethe wires of a pair are close together.Since inductance and capacitancecounteract each other to some extent,the absence of inductance in a cablecircuit means that its capacitance iscompletely unmitigated. In open wirecircuits, where the separation betweenthe wires is usually twelve inches, thecondition is much more favorable totransmission. The attenuation is cor-respondingly less, for the same sizeof conductor, but not as small as itwould be if the inductance were largeenough to offset the effect of capaci-tance. That fact had long been recog-nized, but it didnt help the telephoneengineer much, because he had noconvenient way of increasing the in-ductance of a given telephone line.What he would have liked would havebeen insulated wires in a medium f 940 The Line and the Laboratory
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AIR GAP LOADING COILS Developed for the first transcontinental line. The large coil is for loading the phantom circuit, the small coils for loading the side circuits more magnetic than free air, for thenthe inductance would have been mark-edly greater. That was difficult ofaccomplishment, although years laterit became practicable with the devel-opment of permalloy, when in a sub-marine cable the inductance of thecircuit was increased by wrapping theconductor with a thin tape of thatmagnetic alloy. An obvious way of increasing theinductance of a telephone line, withthe hope of gaining reduced attenua-tion, was to connect coils of wire—wire has more inductance coiled thanstraight—into the line every so often.If the coils had cores of iron, theirinductance would be still higher.That was tried at times, but failedlamentably. The reason we nowknow to have been lack of knowledgeas to the correct spatial separationof the coils along the line. Some idea of all this had been ad-umbrated in

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