Mi) fiiiij. svsrr.M ir.ciixic.ii. jor rx.il 



Means of In-(kr.\sin(; Spekd 



With the speed of operation thus limited there were two ways in 

 which the hniiling speed could he increased; the interference could 

 be reduced, or the strength of signals made greater. No great reduc- 

 tion in interference due to lack of perfect duplex balance could be 

 expected, as balancing networks had already been greatly refined. 

 Extraneous interference in certain cases could be reduced by the use 

 of long, properly terminated sea-earths. The signal strength could 

 be increased either by increasing the sending voltage or by decreasing 

 the attenuation of the cable. However, with duplex operation nothing 

 at all is gained by increasing the voltage in cases where lack of perfect 

 duplex balance limits the speed, and wiili sini|)lex operation any gain 

 from raising the \'oltagc is obtained at tlu- cost of increased risk to 

 the cable, the sending voltage being usually limited to about 50 

 volts by considerations of safety. The attenuation of the cable could 

 be reduced and the strength of the signal increased by use of a larger 

 copper conductor or by using thicker or better insulating material. 

 None of these possilile improvements, h()we\"er, seemed to offer pros- 

 pect of very radical advance in the art. 



In telephony, both on land and submarine lines, an advantage 

 had been obtained b>' adding inductance ' in either of two ways, by 

 coils inserted in series with the line or by wrapjiing the conductor with 

 a layer of iron. The insertion of coils in a long deep-sea cable was 

 practicalh' i)rohibited by difficulties of installation and maintenance. 

 Accordingly, only the second method of adding inductance, com- 

 monly known as Krarii]) or continuous loading, could be considered 



'The idea of improving the transmission of signals over a line by adding dis- 

 tril)Uted indiictanie to it originated with Oliver lleaviside in 1887 (Klectrician, Vol 

 XIX, p. 79, and I-:iectromagneti<- Theory, \ol. I, p. 441, 18W), who was the first 

 to eall attention to the part pla\ed !)>■ inductance in the transmission of current 

 impulses over the cable. He suggeste<l as a means for obtaining increase<l induct- 

 ance the use of iron as a part of the conductor or of iron dust embedded in the gutta 

 percha insulation. He also proposed inserting inductance coils at intervals in a 

 long line. Other types of coil loading were propo.sed by -S. V. Thompson (British 

 I'atent 22,304—1891, and U. .S. Patents 571,706 and 57'l,7()7— 18%), and by C. J. 

 Keed (U. .S. Patents .Sll),612 and .SlO.f.l,? — ISO.?). M. 1. I'upin (A. I. IC. E. trans.. 

 Vol. XVI, p. W, 18'W, and Vol. XVII, p. 445, 1900) was the first to formulate the 

 criterion on the basis of which coil loaded telephone cables could be designed. Con- 

 tinuous loading by means of a longitudinally discontinuous layer of iron covering 

 the conductor was proposed by J. S. .Stone in 1S97 (I'. S. Patent 578,275). Breisig 

 (E. T. '/,., Nov. 30, 1899) suggested the use of an o|)en helix of iron wire wound 

 around the conductor and Krarup (E. T. '/.., April 17, 1902) proposed using a closed 

 spiral so that the adjacent turns were in contact. J. H. Cuntz (U. -S. Patent 977,713 

 fded March 29, 1901) projMJsed another form of continuous loading. Recent general 

 discussions of loacled telegraph cable problems have been given by Malcolm (Theory 

 of Submarine Telegraph and I'elcphone Cable, London, 1917) and by K. W. Wagner 

 (Elrktr. .\achtr. Tech., Oct., 1924). 



