File:Bell telephone magazine (1922) (14753724054).jpg

Identifier: belltelephonemag4344amerrich (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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cable transmission sys-tem radically different from those de-veloped in the past. This is a Pulse CodeModulation System which uses principlessimilar to the carrier system now usedfor trunks between offices in the samecity where circuit requirements are heavy. This system samples the voltages pres-ent on each of the many signals to betransmitted—some 8,000 times a secondin the case of voice circuits. These volt-ages are then encoded and the codesrepresenting all the samples to be trans-mitted are interlaced and sent to theirdestination. Looking at it another way,each individual signal is sent sequentiallyrather than continuously and thereforeoccupies the entire bandwidth for onlyseveral billionths of a second. PCM is a system that approaches atransmission mans dream. It has thetheoretical ability to eliminate cumula-tive distortion and the loss of transmis-sion efficiency that lowers the capacity ofpresent systems when, say, television andvoice signals are sent simultaneously. It 26
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Pre-cast manholes, a recent development, assure uniform high quality construction at lowestpossible cost. Above, a collar is placed on a pre-cast manhole on the new L-4 route in Ohio. appears likely that PCM will permit theconstruction of cable routes with greatercapacity than anything now possible. Communication systems using hollowwave guides and laser beams are alsobeing investigated. This follows the BellSystem policy that its communicationfacilities should take diverse forms. All in all, the entire span of coaxial cablehistory has been marked by continuedand successful efforts to improve and toincrease the capacity of this importantcommunication medium. These accom-plishments point to an increased role forcoaxial cable in the Bell System networkof the future. MILESTONES IN THE DEVELOPMENT OFBROADBAND CABLE SYSTEMS CableCoaxials Carrier Circuits Year Bandwidth Rept. Spacing^ Per Route 1936 2 (.270) IMc 10 Miles 224 1940 4 (.270) 3Mc 5 Miles 600 1945 6 (.270) 3Mc 5 Miles 1200 1947

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