. The Bell System technical journal . which will be described. Origin of Problem For many years the requirements of telephone insulators were rela-tively easy to meet because the frequency of the currents transmitteddid not exceed about 3 kc. and because the leakage of insulators isgenerally low at such frequencies. Therefore, the familiar glass insulators such as are shown in and 2 sufficed, the former design (D. P. type) being employed on thelonger circuits and the latter (toll type) on the shorter ones. Indeedthey still suffice very generally, especially where only currents of voicef
. The Bell System technical journal . which will be described. Origin of Problem For many years the requirements of telephone insulators were rela-tively easy to meet because the frequency of the currents transmitteddid not exceed about 3 kc. and because the leakage of insulators isgenerally low at such frequencies. Therefore, the familiar glass insulators such as are shown in and 2 sufficed, the former design (D. P. type) being employed on thelonger circuits and the latter (toll type) on the shorter ones. Indeedthey still suffice very generally, especially where only currents of voicefrequencies or less are transmitted. The advent of carrier systems employing higher frequencies rangingfrom about 3 to 30 kc. changed the insulator requirements substan-tially. At first these systems were few in number and relatively shortin length and the insulator problem accordingly less important. * Presented at the Summer Convention of the A. I. E. E., Toronto, Out., Canada,June 23-27, 1930. 697 698 BELL SYSTEM TECHNICAL JOURNAL. Fig. 1—Standard D. P. insulator and standard wood pin.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
