File:Bell telephone magazine (1922) (14569806627).jpg

Identifier: belltelephonemag12amerrich (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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a frequency of 22,000 cycles.By choosing a carrier of 40,000 cycles, therefore, and trans-mitting the lower side band, 25,000 to 40,000 cycles, outsideinterference could be minimized. Because facilities for theoperation of carrier apparatus, such as adequate power sup-plies, were available at the toll offices in Philadelphia andWashington, the carrier channels were terminated at these two 171 BELL TELEPHONE QUARTERLY points. Between the toll offices in the two cities and theAcademy of Music in Philadelphia and Constitution Hall inWashington, audio-frequency transmission was employed.These distances were short enough so that neither crosstalk nornoise arising in them was of much consequence. The actual route of the cable is shown in the accompanyingillustration. Regular telephone repeater stations are locatedat Philadelphia, Elkton, Baltimore and Washington. Becauseof the large attenuation at the high carrier frequencies, how-ever, three additional intermediate amplifier stations were
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CMU ROVTt mMDOPHU MMHMCTOn established at Holly Oak, Abingdon and Laurel. At HollyOak the amplifiers were housed in an existing telephone office,but at Abingdon and Laurel small temporary structures wereerected which were just large enough to house the equipmentand to permit an attendant to be stationed there during thedemonstration. The structure at Abingdon was of weldedsteel and is shown in Figures 1 and 2. All of the carrier amplifiers, both at the two terminals and atthe intermediate stations, were especially designed both tobe unusually free from distortion or non-linearity, and to bevery stable with respect to variations in power supply. Ex-cept at the Philadelphia terminal, equalizers, associated withall the amplifiers, were employed to compensate for the differ-ence in attenuation at the various frequencies, so that theoutput of the amplifiers would be at the same level for all fre-quencies. Although the gain introduced at each amplifierstation at the higher frequencies was a

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