File:Bell telephone magazine (1922) (14733083826).jpg

Identifier: belltelephonemag16amerrich (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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Text Appearing Before Image:
ly a Very Narrow Pass Band Can beObtained, but the Addition of Inductance, in Series with the Crystal, Makes ItPossible to Widen Out the Band Over Fifteen Fold. filters with and without the added inductances are shown withtheir characteristics in Figure 6. Further studies by Mason indicated that the inductances inthe side and lattice arms could be wound on the same core andplaced in the side arms as indicated in Figure 7, which is aschematic of the actual filter used in the coaxial cable system. 1 Space does not permit a full explanation of this and other steps in the designof the network. The reader is referred to Masons original paper in the Bell SystemTechnical Journal, July, 1934. 34 THE EVOLUTION OF THE CRYSTAL WAVE FILTER A bridging resistance was also inserted between the sectionsto help in sharpening the cut-off. In addition to these modifi-cations, the circuit finally evolved contains added capacitancesin multiple with the crystal. These capacitances serve to con- In-jl-^^rp^
Text Appearing After Image:
62 63 64 65 66 67 FREQUENCY IN KILOCYCLES PER SECOND Fig. 7. Schematic Diagram of a Quartz-crystal Band-pass Filter, above, andTHE Filter Characteristics, below. trol the width of the pass band and to permit fine adjustment.In the lattice-type network as developed by Mason and em-bodied in the filter under discussion, the quartz crystals are cutin the shape of thin rectangles from 2.4 to4.2 cm. long, and with 35 BELL TELEPHONE QUARTERLY a width of about 50 per cent, and a thickness of 2 or 3 per cent,of the length. The two broad surfaces of the plate are coatedwith aluminum deposited from the vapor in a vacuum chamber.This process, now quite familiar to physicists, is the same asthat employed in making astronomical mirrors. Electricalcontact is made to the metal surfaces through the supportingpoints. Such a crystal has several modes in which it may vibratewhen excited with alternating voltage of appropriate fre-quency. There are five simple modes of vibration: two par-allel to the edg

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