ADVANCES IN CARRIER TELEGRAPH TRANSMISSION 173 



is automatically adjusted to be proportional to that of the incoming 

 signals. 



At any instant the actual voltage between filament and grid is 

 therefore equal to the algebraic sum of (1) the fixed bias voltage Eo; 



130 VOLTS 

 +1 -; POLAR 



I I RELAY 



VOLTS — VOLTS 



GRID- BIAS 

 CIRCUIT 



) COMPENSATOR 

 r" RELAY 

 — (POLAR) 



-=-Ec 



RECEIVING 

 LOOP 



k WAVE-SHAPING 

 CIRCUIT 



COMPENSATOR- 

 > RELAY BIASING 

 CIRCUIT 



COMPENSATOR-RELAY 

 CIRCUIT 



Fig. 6 — Schematic diagram of level compensator. 



(2) the voltage due to the charge on the condenser C; (3) the signal 

 voltage across the secondary of the interstage transformer T; and (4) 

 the drop in voltage across the transformer. By making the detector 

 sensitivity sufficiently great, the signal voltage is caused to overcome 

 the opposing negative bias during a portion of each positive half of the 

 carrier cycles composing a marking pulse, so that a net positive voltage 

 is periodically impressed on the grid causing a flow of current between 

 it and the filament and consequently through the resistance Re and 

 the condenser C in parallel. 



The resulting voltage across condenser C is in the same direction as 

 that of the fixed grid battery Eo and adds thereto. The condenser 

 voltage is determined by the amplitude of the received carrier current, 

 increasing with increased input level and decreasing with decreased 

 input level. By a proper selection of the constants of the circuit, the 

 desired compensation action may be obtained. This action will be 

 such that the change in voltage across the condenser will always, 

 within the effective range of compensation, produce the proper nega- 

 tive grid voltage for unbiased reception of telegraph signals by the 



