Transistor Oscillator for Use in 



Multifrequency Pulsing 



Current Supply 



By F. E. BLOUNT 



(Manuscript received June 30, 1953) 



This paper covers the design and performance of an oscillator using a 

 transistor, in the multifrequency pulsing of digital information over telephone 

 transmission media. The frequencies used are in the range from 700 to 1700 

 cycles per second. 



INTRODUCTION 



A large proportion of the telephone calls made require connections to 

 be set up in more than one central office. Where common control systems 

 are used, this requires that information needed by the second central 

 office be transmitted to it from the first central office which in turn has 

 received its information from the calling subscriber. The "language" 

 used in some cases for transmitting the information is in the form of 

 short pulses of alternating current. Each pulse consists of a combination 

 of two of six available frequencies. Twelve combinations of the six fre- 

 quencies make up the total ''vocabulary". Ten are required for digits 

 and two for special signals sent at the beginning and end of pulsing. This 

 is known as multifrequency, MF, pulsing. The device which controls the 

 pulses is called an MF sender. The device which receives the MF pulses 

 and translates the information received for use by other equipment is 

 called an MF receiver. 



An operator may also use multifrequency pulsing when transmitting 

 information by means of a key set to a distant office. Control of the fre- 

 quencies used is obtained by contacts on the key depressed. Twelve keys 

 are used. 



The previous source of ac was a circuit capable of supplying both op- 

 erator positions and senders. This equipment is however quite expensive. 

 If only a few senders in an office require the MF current the cost per 



1313 



