526 BELL SYSTEM TECHNICAL JOURNAL 



instructions regarding its use and maintenance, have been published. 



Certain classes of equipment cannot be readily treated on a general 

 basis and specific studies of individual cases are required to insure 

 effective application to the railroad use. Where such equipment is 

 requested by the railroad companies the telephone company under- 

 takes the necessary studies and furnishes the apparatus to the railroad 

 companies on a rental basis. 



Extensive use has been made of the various Bell System services 

 by the railroad companies. Examples of the more general applications 

 are: dispatcher and way station telephone sets, selector signaling 

 apparatus, private branch exchanges, loud speaking equipment, cable, 

 telephone repeaters and loading coils. 



The Call Announcer: A Telephone Application of Sound Picture 

 Ideas ^ O. M. Glunt. Fundamental research and development 

 work carried on with a particular objective in one field contributes in 

 many cases to the solution of problems in other fields. A typical 

 example is the application of the sound reproducing elements, devel- 

 oped for use primarily in sound picture theater reproducing systems, 

 in the solution of an intricate problem in telephone system operation. 

 This article outlines the communicating problem which was presented 

 and describes the apparatus which was developed, employing adapta- 

 tions of sound picture principles to meet the need. 



Design and Installation of Toll Cable in the Bell System} Glex 

 Ireland. This paper discusses the present status of the toll cable 

 network of the Bell System, indicates plans for its extension and 

 describes recent improvements in toll cable, including tape armored 

 cable, loading coils and telephone repeaters. Present maintenance 

 methods for toll cable circuits are also dealt with. 



A Rapid Method of Estimating the Signal-to- Noise Ratio of a High 

 Gain Receiver} F. B. Llewellyn. It is shown that a figure of 

 merit for the signal-to-noise ratio in a receiving system is obtained 

 directly by noting how much the total noise output increases when 

 the input circuit is tuned through resonance, in the absence of signal. 

 The effect of mismatching the antenna and input circuit impedances 

 is discussed, and it is concluded that although a small improvement 

 may be obtained in certain ideal cases by making the circuit impedance 

 much higher than the antenna impedance, other considerations 



4 Jour. S. M. P. E., March, \9M. 



^ Proc. Amer. Railzoav Assoc, Telegraph and Telephone Section, Sept., 1930. 



^Proc. L R. £., March, 193 L 



