1068 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



more expensive coils. Higher Q's also produce greater variations in im- 

 pedance and phase with small changes of resonant frequency which re- 

 (luirc much closer control of inductance and capacity with temperature. 

 In the circuit described here the Q has a value of about 100 and its opera- 

 tion is quite satisfactory'. The tank circuit is coupled through the small 

 condenser Cz to the diode Dz . This diode ties the positive peaks of the 

 timing wave to ground as is reciuired for inverted pedestal timing. The 

 network N pro^'ides the timing delay needed for optimum repeater per- 

 formance. 



2.4 DC Compensation in Timing Wave 



The timing wave amplitude from the tank circuit is insufficient to allow 

 it to be applied directly to the emitter of the blocking oscillator. Conse- 

 quently in the interest of circuit simplicity the signal amplifier is used 

 for the timing wave as well. To avoid the complications introduced by 

 dc coupled circuits when close bias tolerances must be maintained, the 

 amplifier was coupled to the blocking oscillator by condenser C2 . This 

 presents a problem as to how to neutralize the charge the dc component 

 of the timing wave builds up on C2 . The means by which this is accom- 

 plished can be more easily understood by referring to Fig. 4. 



In this figure the time constant of the feedback loop RoCiRi , is made 

 large so that substantially equal charges are added to Ci by each regen- 

 erated pulse. In the timing loop this is also nearly true even though noise 



INPUT 



T 



yf 



Cp 



REGENERATIVE 

 REPEATER 



R, 



:C, 



.^ A A _. 



V V ^ 



X 

 X 



c 



T 



Roy r^i 



x'' 



OUTPUT 



Fig. 4 



QUANTIZED FEEDBACK 



Method for maintaining the dc values of timing wave. 



