Abstracts of Bell System Technical Papers Not 

 Appearing in this Journal 



Commercial Loading of Telephone Cables. \V. Fondii.ler.' The 

 application of loading coils to exchange area cable and to toll cable 

 is discussed and data given on the loading coils and the transmission 

 characteristics of loaded cable circuits. 



An important section of the paper deals with the reciuireincnts for 

 loading phantom circuits. In particular, the crosstalk and noise 

 requirements for phantom loading are analyzed. 



The paper concludes with a comparative study of three s\stems 

 of phantom loading which are in commercial use, viz., the Campbell- 

 Shaw, the Kbling and the Olsen-Pleijel system. It is concluded that 

 the Campbell-.Shaw phantom loading system, which has been adopted 

 as standard by the Bell .System, as well as by many European Ad- 

 ministrations (notably the British Post Office), has marked advantages 

 over the other two systems which ha\e been used to a minor extent 

 in continental Europe. 



The Schotlky Effect in Low Frequency Circuits- by J. B. Johnson. 

 This effect, discovered b>- Schottky, which depends on the probability 

 of fluctuations of electron emission from a filament, has been measured 

 over a considerable range of conditions in resonant circuits of which 

 the natural frccjuency was varied from 8 to nearly (5000 p.p.s. The 

 efTect is much larger in the lower range of frequencies than the theory 

 predicts. With a tungsten filament, the ratio of observed to theoreti- 

 cal effect e'/e is about .7 for frequencies above 200, but increases 

 rapidly to 50 at 10 cycles per sec. With an o.xide coated filament, the 

 ratio increases from 1 at 5000 cycles to 100 at 100 cycles. This is 

 interpreted to mean that the emission of electrons is not strictly chaotic 

 i)ut is influenced by irregular temporal changes in the cathode emis- 

 sivity. In a high frequency circuit these changes become impercept- 

 ible and the emission is effecti\ely random. When current is limited 

 by space charge the .Schottky elTect decreases because of the interaction 

 of the electrons, and other disturbances may act upon the space charge 

 so as to completely mask the remanent Schottky eff'ect. The mag- 

 nitude of the disturbances in amplifying vacuum tubes can therefore 

 not be predicted from measurements on the true Schottky effect. 



A Note on Schottky s Method oj Determining the Distribution of 

 Velocities Among Thermionic Electrons,' C. Davisson. Limiting con- 



' tktirical Cuinniunication, July, 1925. 



• Physical Review, Vol. 26, No. 1, page 71, July, 1925. 



• Physical Review, Vol. 25, No. 6, page 808, June, 1925. 



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