1316 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



8. Provide an output impedance sufficiently low that the differences 

 in impedance of the associated oscillator will not appreciably affect either 

 output level or frequency. 



9. Meet frequency requirements when working into trunks that have 

 impedances with phase angles of +15° to —45°. 



10. Be unaffected by transient disturbances on trunk conductors 

 coupled to the oscillator. These disturbances are caused by lightinng 

 or troubles on closely associated power lines. 



DISCUSSION 



There are many ways of making a transistor oscillator. One of the 

 simplest and most stable of these uses an LC circuit for controlling the 

 frequency. Additional windings inductively coupled to the tuned circuit 

 inductance provides the necessary feedback to the transistor and the 

 connection to the load. This is the type of circuit adopted for this ap- 

 plication. A schematic of the circuit is shown in Fig. 2. The transistor 

 controls power supplied to the oscillatory circuit during only one half 

 the operating cycle. The amplitude of the ac voltage produced across 

 winding 1-2 is almost equal to the dc voltage applied to the collector. 



The transistor acts as an amplifier or it may be considered as a nega- 

 tive resistance. Control of the transistor is obtained by current flowing 

 in the emitter that is in phase with the collector voltage. To build up 

 oscillations, the power put into the circuit must be greater than that 

 expended. Stability is obtained when the power put in equals the power 

 expended. 





|-A/W 



I APPROX 3' 



jL z:^ 10,000 



JJ./LLF 



T" 



10.5 VAC 



■vw 



0.25V 

 Vb 



— .TO LOAD 



^^^ \2.2V 



RMS 



■Wv — I 



'b_ 



6.25V 



45-50 VOLT 



CENTRAL OFFICE 



BATTERY 



TO OTHER FIVE 

 OSCILLATORS 



Fig. 2 — Oscillator circuit for MF signaling showing approximate values for 

 voltages. 



