TRANSISTOR OSCILLATOR FOR MULTIFREQUENCY PULSING 1315 



sender becomes very large. It was for this reason that transistor oscilla- 

 tors were developed for use as individual current supplies. 



An individual sender will handle a large number of calls during a day 

 but the aggregate time during which the multifrequency current is re- 

 quired is normally less than two hours. The ability of transistors to op- 

 erate the instant that power is applied is therefore a distinct advantage 

 in saving power. The low voltage that is required for their operation and 

 the long life expectancy are further advantages. 



The method used is illustrated in Fig. 1. To transmit a pulse the out- 

 put windings of two oscillators are connected in series through two 

 410-ohm resistors and the parallel combination of a 580-ohm resistor and 

 windings on a transformer. The other windings on the transformer are 

 connected to the trunk conductors. At the distant office the trunk is 

 terminated by a similar transformer. The output of this transformer is 

 connected to an ampUfier, filter circuits and detectors in an MF receiver. 

 Relays associated with the detectors convert the ac signal into a dc 

 signal for the register circuit. 



The 580-ohm resistor across the transformer winding serves as a ter- 

 mination for the trunk between pulses. This resistor in combination with 

 the two 410-ohm resistors in the oscillator circuits serve as the trunk 

 termination during pulsing. 



REQUIREMENTS FOR OSCILLATOR 



This oscillator was designed to be used in place of an existing piece of 

 equipment. It therefore must have the properties of the existing equip- 

 ment on which the design of equipments that are associated with it 

 have been predicated. 



The requirements are then : 



1. Operate at 700, 900, 1100, 1300, 1500 or 1700 cycles per second ± 

 1 per cent. 



2. Furnish ac signals at a level of —3 dbm ifc 1 db at the input to the 

 trunk. 



3. The level difference at all frequencies must be no greater than 1 db. 



4. Attain normal output level between the time the sender is seized 

 and the time the first pulse is sent. This time is approximately one half 

 second. 



5. Meet all requirements with dc input voltage limits of 45-50 volts. 



6. Meet all requirements with ambient temperatures of +40°F to 

 + 135°F. 



7. Have level of second harmonic a minimum of 35 db below the 

 fundamental. 



