Improvements in Communication Transformers * 



By A. G. GANZ and A. G. LAIRD 



The rapidly advancing art of electrical communication and the increas- 

 ingly wide variety of its applications have required marked improvements 

 in the transformers used in communication circuits. These improvements, 

 achieved partly through advances in design and partly through improve- 

 ments in the constituent materials, are discussed in this paper. 



THE rapid development of the art of electrical communication in 

 the last decade has necessitated marked improvements in the 

 transformers used in it. New applications for these transformers and 

 the extension of old ones have imposed new and far severer perform- 

 ance requirements. The primary applications of communication 

 transformers are in the telephone plant, in the various voice and 

 carrier transmission circuits, and in a multitude of incidental services. 

 They have also wide uses in radio broadcasting transmitters and re- 

 ceivers, in the amplifiers of sound motion picture equipment, in the 

 radio equipment for aircraft, and in a variety of other circuits. 



Although communication and power transformers have a common 

 origin, the communication transformer now has evolved as a precision 

 device which has only a general resemblance to the usual power trans- 

 former. Some voice-frequency transformers, such as those used in 

 aircraft, weigh but 2 or 3 ounces, yet transmit speech substantially 

 undistorted. Some used in program circuits transmit with negligibly 

 small phase or amplitude distortion all frequencies from 20 to 16,000 

 cycles per second. Transformers also have been developed for trans- 

 mitting narrow bands of frequencies and having associated with the 

 normal transformer performance valuable frequency discriminating 

 properties. A discussion of improvements in these narrow band trans- 

 formers is outside the scope of this paper, which will be confined to 

 those transmitting wide-frequency bands, that is, those for which the 

 ratio of upper to lower limiting frequencies is at least 10 to 1. 



The design of the modern communication transformer is based upon 

 extensions of the familiar theory of transformers covered in numerous 

 texts. However, this type of transformer is a more complex device, 

 with its multiplicity of requirements and its transmission over a wide- 

 frequency range. Its proper representation accordingly requires a 



* Published in the December 1935 issue of Electrical Engineering, and scheduled 

 for presentation at the Winter Convention of the A. I.E. E., New York City, Janu- 

 ary 28-31, 1936. 



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