﻿IS?-!*.] L. Schwendler — On the general Theory of Duplex Telegraphy. 17 



A' 

 can be transformed* into E'-—, wliich is egual top', or we have generally 



S = p 



i. e. the difference of forces ly which duplex and single signals in the same 

 station are produced is equal in magnitude and sign to the force hy which 

 balance in that station is disturbed. 



Consequently tlie rigid fulfilment of the first condition (D = 0) 

 will entail the rigid fulfilment of the second condition (S = 0) and this 

 it will be clear is only due to the fact that the complex resistance p is in- 

 dependent of b, and that the key during signalling does not alter p ; whence 

 it follows that the perfection of the key in this respect is of the greatest 

 importance. There are, however, no practical difficulties connected with the 

 construction of a key which fulfils condition (VII) perfectly. 



By the aid of the relations given in equations (VI) and (VII) we have 

 therefore gained the great practical advantage, that Duplex Telegraphy 

 will be entirely on a par with single Telegraphy, if the means of attaining 

 rigid balance are sufficiently accurate, convenient and rapid. 



But, even supposing that we are unable to keep that balance rigidly 

 for any length of time (on account of L varying), we can nevertheless bring 

 the regularity of duplex working as near as possible to that of single work- 

 ing by making D and S as small as possible for any given variation of L, 

 Rapid approximation oftJie two functions D and S towards zero. 



For station I we had 



s'=p-«^f-i;^ (IV-) 



which we may also write 



m' \l/' 



* We have 



k 



N = 



n 



mk — An 



b 



E b A 



mk — A n 



E b A 



bN 



E A 



= — = p 



