TRANSISTOR OSCILLATOR FOR MULTIFREQUENCY PULSING 1329 



If however the voltage becomes sufficient to breakdown one of the pro- 

 tector blocks that are connected between each trunk conductor and 

 ground, a voltage comparable to the breakdown potential of the pro- 

 tector blocks (400 to 600 volts) would then be impressed across the out- 

 put windings of the transformer. The usual cause of this (condition is 

 lightning. However, neither artificially simulated lightning nor transi- 

 ents of longer duration were capable of raising the voltage on the tank 

 circuit to the point where a transistor was damaged. This is due both to 



R (SERIES) + - 

 SUM (-R) -H (+R) IS NEG SUM (-R) + (+ R) IS POS 



Fig. 15 — Relationship of shunt to series resistance. 



the high energy level of the tank circuit and the isolation furnished be- 

 tween repeating coil and oscillator by the series resistors. 



summary: 



The transistor oscillator adequately fulfills the requirements for a 

 source of current for multifrequency pulsing over telephone transmission 

 circuits. Adjustments are provided so that the requirements for frequency 

 stability, harmonic level and output level can be met with transistors 

 having a wide range of characteristics. Sufficient margin is provided by 



