The Bell System technical journal (1922) (14756107485)

Identifier: nasasystemtechni172amerrich (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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alance, greatly reduces the amount of the oddharmonics present in its output. Odd harmonics are obtained at onepoint and even at the other. This separation into odd and even har-monics by the balance of the copper-oxide bridge provides effectiveloss of about 30 to 40 db and reduces the requirements on the carriersupply filters which follow. The two branches pass through hybrid coils to the banks of channelcarrier supply filters. These separate the frequencies and feed themto twelve carrier supply bus bars, one for each channel frequency.From these the individual modems are fed through protective resis-tances so that an accidental short circuit on one of the modems willnot cut off the carrier supply to the others. The hybrid coils permit the two generators to be connected so thateither can feed into the same bank of channel carrier supply filterswithout being reacted upon by the other. No switching is requiredwhen changing from regular to emergency supply. BELL SYSTEM TECHNICAL JOURNAL

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;L CABLE CARRIER TELEPHONE TERMINALS 115 H The 120-kc. carrier which feeds the group modulators of ten systems^r a total of one hundred and twenty talking channels must be very-dependable. Therefore separate filters are used for the regular andemergency supply and separate amplifiers for the large power requiredby group modulators. Regular and emergency distributing buses areprovided. Each group modulator and each group demodulator iswired through protective resistances to the regular bus and throughanother set of protective resistances to the emergency bus. With thisarrangement an accidental short circuit even across one of the bussesor across one of the output coils of one of the 120-kc. amplifiers will notstop the whole supply of 120 kilocycles. The 4-kc. oscillator of the emergency generator is in constantoperation so that when it is needed no time is required to start it,but the grid bias on the second tube is held above its cutoff value bythe automatic transfer circuit. This pre

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1922

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