CERT.IIX r.lCTORS .iriliCTLXG TLLEGKArU Sl'EED 325 



eniplDvinK ilircct currents will next be considereil. This will he fol- 

 lowetl by .1 consiileration nf the more coniplicaied case of trans- 

 mission over lonvj submarine caiilcs. 



It will be shown that the waves prmluceil i)y sending rectangular 

 signal elements through suitable electrical networks which round 

 them off before they are impressed on the transmitting medium are 

 probably l)est in most cases. C'omparsion will be made between 

 waves shajied by sending rectangular signal elements through suitable 

 networks and waves made up of half cycles of a sine wave, bringing 

 out the inferioriiN' of the latter. 



niRi;( r-C I RRi.NT Ti:i.ii(iRAiH Transmission Ovkr a 



DiSTORTIONLKSS LlNK 



Before proceeding with tliis discussion two terms, which will be 

 used in this paper, and which are considered to be of fundamental 

 importance, will be defined — -"signal element" and "line speed." It 

 is usually possible, especially when sending is done mechanically, 

 to divide the time into short intervals of approximately equal duration, 

 such that each is characterized by a definite, not necessarily constant, 

 voltage impressed at the sending end. The part of the signal which 

 occupies one such unit of time will be called a "signal element." 

 For example, the letter a in ordinary land telegraphy will be said to 

 be made up of five signal elements, the first constituting a dot, the 

 second a space and the next three a dash. The "line speed," as 

 used in this paper, equals the number of signal elements per second 

 di\ ided by two. In ordinary land telegraphy the line speed is equal 

 to the dot frequenc\' when a scries of clots separated by unit spaces 

 is transmitted. 



The discussion will first be limited to the case of direct-current 

 telegraphy over a distortionless line. This case is the simplest, and 

 in addition the results will aid in understanding the more complex 

 cases. It may aid in obtaining an understanding of this case to 

 assume that the distortionless line is made up simply of series and 

 shunt resistances. 



A distortionless line, such as the one which has been assumed, 

 will transmit all frequencies with equal efficiency from zero upward. 

 In considering applying direct-current telegraph to this line, it will be 

 assumed that the telegraph circuit will have assigned to it only a 

 limited range of frequencies from zero upward, the remaining fre- 

 quency range being assigned to some other uses, such as ordinary 

 telephone and carrier telephone and telegraph. It will also be as- 



