CERTAIN FACTORS AFFHCTIXG TFI-FCKAl'll SfF.FD 335 



place, there is a theoretical increase in the ratio of l.():I which ac- 

 companies the chalice from the l\vo-current-\alue to the three-current- 

 value C(Hle. In the second place, there is an incidental increase in tlie' 

 ratio of 1.4:1, due to the fact that the present two-currcnt-valiie codes 

 are lonjjer than would l>e necessary, if receiving were done l)y means 

 other than the ear. The total increase in going from the two-current- 

 value Continental or American Morse codes to the three-current- 

 value Continental ccxie is, therefore, in the ratio of 1.6X1.4:1 or 

 2.2:1, provided the line speed is the same. In this connection it 

 should be noted that in the case of the American Morse, the ratio 

 is prohahly somewhat less than this for the reasons pointed out above. 



LiMlT.ATiONS IN APPLYING CoDES WITH MoRK TII.W 



Two Current Values 



Certain inherent limitations which have to do with how much the 

 numl)er of current values can be ad%antageously increased are as 

 follows: 



1. l-"luctuations in transmission ct"ticienc\' of the circuit, 



2. Interference, 



3. Limitations on the power or voltage which it is permissible to 

 employ. 



In addition it may be stated that, in general, whenever more than 

 two current values are employed it is neces.sary to make the sending 

 and receiving means more complicated and expensive. There may 

 be nothing to gain, therefore, in using codes other than those made 

 up of two current values where the telegraph circuits are cheap. 



Considering now the features which limit the number of current 

 values which can be employed, it is believed that the importance of 

 the first factor will be obvious. If the line is subject to fluctuations 

 so that the stronger currents at certain times become less in magni- 

 tude than the weaker currents at other times, it will be impossible 

 to discriminate between the different current strengths making up 

 the code, particularly if the fluctuations are rapid. 



In connection with interfering currents, it is evident that these 

 may Ijc of such polarity as to add to or subtract from the signaling 

 currents and it is consequently necessary to separate the various 

 current values employed sufficiently so that one current value with 

 the interference added may be distinguished from the next larger 

 current value with the interference subtracted. 



The spacing between the current values being determined by the 

 interference and fluctuations in transmission efficiency, it will be 



