MAGNETIC DRUM TRANSLATOR FOR TOLL SAVITCHING OFFICES 709 



takes place in cooperation with crossbar and other relay-type switching 

 equipment typical of the present-day telephone office, thus providing an 

 environment suitable for obser\'ing the behavior of fast pulse circuits in 

 the presence of electrical disturbances. Finally, there exists a relatively 

 new piece of apparatus which now performs the translation function, 

 nair.ely the card translator. Thus, if an exact one-to-one alternative for 

 the card translator were constructed employing a magnetic drum, full 

 advantage could be taken of the testing procedures already de\'eloped 

 and a comparison could be made against a norm of performance; further- 

 more, a field trial would be possible, if desired, with a minimum of inter- 

 ference with normal operation of the telephone plant. 



It was decided, therefore, to build a full-scale magnetic drum trans- 

 lator which could substitute for a card translator in order to obtain lab- 

 oratory e.Kperience with apparatus of this type and to determine its adapt- 

 ability to telephone standards and practices. The completed equipment 

 is shown in Fig. 1. The equipment on the one frame illustrated is the 

 equivalent in function and capacity of one card translator with its asso- 

 ciated table. This magnetic drum apparatus is not aimed at replacing the 

 card translator, which is a well-engineered device known to give satis- 

 factory service in day-to-day operation. For evaluation purposes in this 

 article, however, it is assumed to be competing with the card translator. 

 The following sections describe the design features and operating de- 

 tails of the translator which was constructed. A brief description of the 

 card translator and that portion of the 4A office in which the drum trans- 

 lator must function has been included to provide the necessary back- 



, ground for the description. It will become evident that the requirement 

 of interchangeability which necessitates a one-to-one equivalence with 



I the card translator has imposed on the drum translator a number of re- 

 strictions which are not inherent in it. These tend to prevent full exploita- 



j tion of the speed and code advantages which might be realized with the 

 drum. Furthermore, the rapidity with which all of the information on the 



' drum is presented on a continuous read-out basis would permit a type of 



i centralized operation which will be touched on briefly and which would 



i seem to offer apparatus economies not attained in the test model. None 

 of these factors, however, impairs the usefulness of conclusions which 



! may be drawn from test results concerning reliability. 



SURVEY OF MAGNETIC RECORDING PRINCIPLES EMPLOYED IN THE TRANS- 

 LATOR 



All magnetic drums have certain features in common : they consist of 

 a means of moving a thin shell of magnetically-hard material rapidly 



