ADVANCES IN CARRIER TELEGRAPH TRANSMISSION 201 



respectively, and that the interstage transformer is perfect. The tube 

 resistance which is effective during the conducting period may be 

 included in R and considered constant, as it is relatively small compared 

 to the other resistances involved. 



In describing the principle of action of the level compensator, it has 

 been pointed out that for proper compensation the point of relay 

 operation AA (Fig. 7) should bisect the crest value of the signal pulse 

 in each case. In this figure, the three envelopes shown correspond to 

 very short signal pulses; if the signals were sufficiently long so that a 

 steady marking condition were reached, as is usually the case, the crest 

 of the signal would coincide with the peaks of the steady carrier wave, 

 and AA would bisect its positive loops. 



For long signals the condition for proper compensation is therefore 

 that the relay will just operate at one-half the steady-state carrier 

 voltage. This is true for all carrier voltages E which equal or exceed 

 the value required to make the grid positive. In the particular cdse 

 where E just fails to cause the condenser to charge, E = — Eo and the 

 relay operates when a value — Eo/2 is reached. For any other greater 

 value of E it is necessary in addition to overcome the voltage due to 

 the charge on the condenser before the relay will operate. The cri- 

 terion for perfect compensation where signals are of sufficient duration 

 so that the steady state is reached is therefore: 



f + f-.. = o, (1) 



where E is the maximum value of the instantaneous steady state 

 carrier voltage, and E, Eq are arbitrarily taken with such polarities 

 as to urge the mesh current ia in the direction indicated in Fig. 25B, 

 while Be is negative because it opposes the current ia which gives 

 rise to it. 



Substituting Cc — Q/C in (1) we have 



where Q is the average charge existing on the condenser during a long 

 mark for any particular value of E. The problem of compensation 

 then resolves itself in adjusting the constants C, R, Re, and Eq so that 

 relation (la) will hold; in other words an expression for Q must be 

 found in terms of these parameters. The problem is not susceptible 

 of explicit solution, but expressions will be derived which are believed 

 to clarify the operation of the compensator and permit computation. 



