Abstracts of Technical Articles by Bell System Authors 



Automatic Ticketing of Telephone Calls} 0. A. Friend. In January a 

 new arrangement of dial central office equipment was placed in service at 

 Culver City, California, designed to enable subscribers to dial for them- 

 selves their short-haul toll calls to other exchanges within the Los Angeles 

 metropolitan area. These calls were formerly placed with an operator, who 

 completed and timed the call and wrote a ticket used for billing. The new 

 equipment controls the automatic completion of the dialed call, identifies 

 the calling line, and prints a ticket showing the calling and called numbers 

 and other information needed for billing. The arrangement appUes to the 

 step-by-step switching system and employs senders capable of routing these 

 calls efficiently through a metropolitan trunking network. It affords op- 

 erating economy together with faster and more convenient service. 



Noise Figures of Radio Receivers.- H. T. Friis. A rigorous definition of 

 the noise figure of radio receivers is given in this paper. The definition is 

 not limited to high-gain receivers, but can be applied to four-terminal net- 

 works in general. An analysis is made of the relationship between the noise 

 figure of the receiver as a whole and the noise figures of its components. 

 Mismatch relations between the components of the receiver and methods of 

 measurements of noise figures are discussed briefly. 



Structural Features of Buna S — Relation to Physical Properties.^ A. R. 

 Kemp and W. G. Straitiff. The non-symmetry in the chain structure of 

 Buna S hydrocarbon is discussed in relation to the prevention of crystalliza- 

 tion and the impeding of cross linking during vulcanization. This lack of 

 chain symmetry is put forward to account for the poor quality of Buna S 

 vulcanizates in comparison with corresponding vulcanizates prepared from 

 natural rubber. Fractionation data on a regular benzene-soluble crude 

 Buna S indicates the presence of an objectionable broad range of polymer 

 sizes. It is shown that the lowest-molecular-weight polymer fractions in 

 Buna S are not chemically bound in the vulcanizate but remain soluble in 

 chloroform. By removing most of this low polymer from Buna S, the 

 chloroform extract of its vulcanizate decreases accordingly. Vulcanizates 

 were prepared from high- and low-molecular- weight fractions of Buna S. 

 The high fractions were tough, dry, and difficult to handle on the mill; the 



^Elec. Engg., Transactions Section, March, 1944. 



^Proc.I. R. E., July, 1944. 



^ Indus. & Engg. Chem., August, 1944. 



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