File:The Bell System technical journal (1922) (14756491305).jpg

Identifier: bellsystemtechni12amerrich (find matches)
Title: The Bell System technical journal
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company
Subjects: Telecommunication Electric engineering Communication Electronics Science Technology
Publisher: (Short Hills, N.J., etc., American Telephone and Telegraph Co.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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in two and used, one half for transmission in one direction,the other half for transmission in the other. Fig. 2 compares the OPENWIRE TYPED TYPEC-N TYPEC-S TYPEC-T MORRISTOWNCABLE DOTTED ARROWS SHOW LOCATIONOF CARRIER FOR EACH BAND ; EAST TO WEST ; WEST TO EAST TNORTH TO SOUTH j SOUTH TO NORTH 3 2 I ♦ ♦ 15 20 25 FREQUENCY IN KILOCYCLES Fig. 2—Frequency allocations of carrier telephone systems. frequency allocation of the Morristown cable carrier system withexisting open-wire systems in this country. Except for this matter ofdifference in frequency allocation, the fundamental carrier methodsused in this cable system did not differ in principle from those alreadyused on open wires. As will be noted in Fig. 2 all of these carriertelephone systems use the single sideband method of transmission withthe carrier suppressed. Fig. 3 is a schematic diagram of the terminal apparatus used inderiving one of the telephone circuits. Its general resemblance to 254 BELL SYSTEM TECHNICAL JOURNAL

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Fig.3 — Terminal of one telephone circuit.

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nsw—5 CARRIER IN CABLE 255 the terminal apparatus used in present open-wire systems is evidentso no further discussion of this seems required. Fig. 4 shows fiverelay rack bays carrying terminal equipment (exclusive of lineamplifiers) for one system terminal yielding nine telephone circuits.Important problems in cable carrier transmission are: 1. Keeping circuits electrically separated from each other, i.e., pre- venting troublesome crosstalk. 2. Maintaining stability of transmission. Crosstalk With respect to crosstalk, the first and most important requirementis to secure a very high degree of electrical separation between pathstransmitting in opposite directions. Careful crosstalk tests demon-strated that by placing east-going circuits in one cable and west-goingcircuits in another, the necessary degree of separation could be ob-tained even though the two cables were carried in adjacent ducts.Tests on short cable lengths indicate that adequate separation canprobably be secured by m

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