LOADED LINES AND COMPENSATING NETWORKS 415 



their impedance characteristics, because the recei\cd energy depended 

 much more on the former than on the latter. Indeed, the object of 

 loading ■ was to improve the propagation characteristics of trans- 

 mission Hnes; the effects on the impedance characteristics were inci- 

 dental, and of quite secondary importance. 



The application of the two-way telephone repeater greatly altered 

 the relative importance of these two characteristics, decreasing the 

 need for high transmitting efficiency of a line but greatly increasing 

 the dependence of the results on the impedance of the line. As well 

 known, this is because the amplification to which a two-way repeater 

 can lie set witl-.out singing, or even without serious injury to the 

 intelligibility of the transmission, depends strictly on the degree of 

 imf)edance-balance lietween the lines or between the lines and their 

 balancing networks. In the case of the 21-type repeater the two 

 lines must closely balance each other throughout the telephonic 

 frequency range. In the case of the 22-type repeater, which for long 

 lines requiring more than one repeater is superior to the 21-type, 

 impedance-networks are required for closely balancing the impedances 

 of the two lines throughout the telephonic frequency range. Such 

 balancing networks are necessary also in connection with the so-called 

 four-wire repeater circuit.' 



In Parts I, II, and III of this paper there is presented in a simple 

 yet fairly comprehensive manner the dependence of the characteristic 

 impedance of periodically loaded lines (of the series type) on the 

 frequency and on the line constants, by means of description accom- 

 panied by equations transformed to the most suitable forms and by 

 graphs of those equations. Also, the dependence of the attenuation 

 constant on the frequency is presented to the extent necessary for 

 exhibiting the disposition of the transmitting and the attenuating 

 bands and thus enabling the characteristic impedance to be described 

 with reference to those bands, and the important correlation between 

 the characteristic imfjedance and the attenuation constant thereby 

 exhibited; for the characteristic impedance by itself is not fully 

 significant. 



Parts I\' to \'III, inclusive, relate to the simulation and the com- 

 pensiUion of the impedance of periodically loaded lines by means of 



' For the fundamental the<>r\ of loaded lines, reference may be made to the original 

 papers of Piipin and of C'amplicll (Pupin: Trans. A. I. E. E., March 22, ISW and 

 .Mav 19. 1900; Electrical IVorU, October 12, 1901 and March I, 1902. Campbell: 

 PhU. Mag.. March, 1903). 



' Regarding the broad subject of repeaters and repeater circuits, reference may be 

 made to the paper bv Gherardi and Jewett: "Telephone Repeaters," Trans. 

 .^. 1. E. E., 1919, pp. 1287-1345. 



