436 BELL SYSTEM TECHNICAL JOURNAL 



line while speech is being transmitted in the opposite direction on the 

 other side. This device is known as an "echo suppressor." ■* 



The enormous increases in long distance telephone traffic together 

 with the necessity of providing better transmission quality in con- 

 nection with radio broadcasting ^ and trans-oceanic messages, have led 

 to continuous design changes in telephone plant with more exacting 

 requirements for manufacture. To permit adequate and prede- 

 termined spacing of loading coils and repeater stations, the cable 

 design must be such as to insure definite capacitances per mile. There 

 must be a minimum of unbalance between circuits to insure that inter- 

 ference or 'crosstalk" is held to a low value. To handle the ever in- 

 creasing load of messages promptly and to secure further overall 

 economies, cables are being designed with a greatly increased number 

 of wire pairs, but of approximately the usual outside diameters to 

 permit the use of existing cable ducts. All of these design problems 

 are reflected in the machinery and methods of manufacture. 



Manufacture of Cable ^ 



A typical long-distance telephone cable (toll cable) consists of 

 "quads" (double pairs) of paper-insulated electrolytic copper wire 

 (No. 16 to No. 22 B. & S. gauge) built up in layer construction and 

 covered with a lead-antimony alloy sheath 2f in. in diameter and | in. 

 thick. (Fig. 4.) 



The raw materials for such cable consist of high-grade lead in pig 

 form, annealed electrolytic copper wire, and large jumbo rolls of 

 manila-rope wood-pulp paper. The first operation consists of slitting 

 the large rolls of paper into disk-shaped pads (Fig 5) . A sufficient num- 

 ber of these pads are placed in an insulating machine which applies the 

 paper to the copper wire in spiral form at a head speed of from 1,470 to 

 2,400 r.p.m. (Fig. 6). The insulated wires are paired very carefully and 

 then placed in a machine which first twists the pairs and then forms 

 them into twisted quads (Fig. 7). 



The quads of wire thus built up are placed into a strander. One 

 quad serves as a center about which other quads are laid in alternate 

 layers as the material progresses through the machine (Fig. 8). Step 



*A. I. E. E. Proceedings, Vol. XLIV, "Echo Suppressors for Long Telephone 

 Circuits," by A. B. Clark and R. C. Mathes. 



^ Bell Sys. Tech. Jour., July 1930, "Long Distance Cable Circuit for Program 

 Transmission," By A. B. Clark and C. W. Green. 



^ See paper " Recent Developments in the Process of Manufacturing Lead-Covered 

 Telephone Cable," by C. D. Hart, for historical treatment and developments 

 prior to 1927 — presented at the Regional Meeting of District No. 5 of the A. L E. E., 

 Chicago, Illinois, November 28 to 30, 1927. Published in Bell Sys. Tech. Jour., 

 April, 1928. 



