CONQUEST OF DISTANCE BY WIRE TELEPHONY 395 



which was available could not be used as an adjunct to loading, and even 

 on non-loaded lines its use was greatly restricted. 



From 1916 on, the vacuum tube repeater was recognized in its own right 

 and potentialities as an independent instrumentality for improving trans- 

 mission. For nearly a decade, repeaters and loading were competitors in 

 the open-wire plant, sometimes used together as a team. Beginning in 

 1916, loading was removed from many 165 mil lines on which it was planned 

 to use repeaters, and this practice continued at an accelerating rate during 

 the early twenties to facilitate the exploitation of open-wire carrier tele- 

 phone systems. GEC-812, issued June 1918, definitely discouraged the 

 provision of loading on new 165 mil circuits. On 104 mil circuits, however, 

 the competition between loading and repeaters was much closer. Partly 

 due to production limitations on repeaters, the mileage of loaded 104 mil 

 circuits increased rapidly during the war period, and reached a peak about 

 1923. Not long afterwards, the practice of loading 104 mil circuits stopped 

 and the removal of existing loading accelerated, so as to provide maximum 

 plant flexibility for the use of repeaters and open-wire carrier telephone and 

 carrier telegraph systems. '" On all types of non-loaded Imes used in conjunc- 

 tion with repeaters, however, loading continued to have an important func- 

 tion in the transmission treatment of the unavoidable incidental cables. 



In the long distance cable field, repeaters and loading were continuously 

 developed over a period of more than two decades to work together as equal 

 partners in a team, each making its own optimum contribution on a basis 

 that provided the desired over-all transmission performance at about the 

 minimum total cost. 



Development Work 



Returning to the evolution of the continental backbone line network in 

 terms of repeatered non-loaded 165 mil lines, it was fully appreciated at the 

 beginning that because of the increase in the number of repeaters and the 

 changes in the line, improved types of repeaters and auxiliary apparatus 

 would be required. The principal need was an improvement in the gain- 

 frequency characteristic. This involved among other matters a reduction 

 of the frequency distortion characteristics of the auxiliary apparatus. It 

 was also found desirable to stabilize the repeater gain and to improve the 

 impedance of the repeater presented to the line so that it would more closely 

 match the line impedance. 



During 1917 and 1918, analyses of extended tests on repeatered lines and 

 cables laid the foundation for computation techniques that enabled the over- 

 all transmission performance of repeatered circuits to be predicted with 



1" It was not until 1934, however, that the use of open-wire loading ceased completely. 



