400 BELL SYSTEM TECHNICAL JOURNAL 



plane-to-ground communication. An experimental investigation of 

 these conditions over the available frequency range has been carried out 

 and the results are described. 



A complete aircraft radio telephone system designed for the use of 

 air transport lines and an airplane radio receiver designed for reception 

 of government radio aids to air navigation are also described. 



A Study of Noise in Vacuum Tubes and Attached Circuits. '^ F. B. 

 Llewellyn. The noises originating in vacuum tubes and the attached 

 circuits are investigated theoretically and experimentally under three 

 headings: (1) shot effect with space charge, (2) thermal agitation of 

 electricity in conductors, (3) noise from ions and secondary electrons 

 produced within the tube. 



A theoretical explanation of the shot effect in the presence of space 

 charge is given which agrees with experiment insofar as a direct deter- 

 mination is possible. It is shown that the tubes used should be capable 

 of operating at full temperature saturation of the filament in order 

 to reduce the shot effect. 



In the computation of the thermal noise originating on the plate 

 side of a vacuum tube, the internal plate resistance of the tube is to 

 be regarded as having the same temperature as the filament. 



Noise produced by ions within the tube increases as the grid is 

 made more negative. 



With tubes properly designed to operate at temperature saturation 

 it is possible to reduce the noise on the plate side to such an extent 

 that the high impedance circuits employed on the grid side of the 

 first tube of a high gain receiving system contribute practically all of 

 the noise by virtue of the thermal agitation phenomenon. 



On the Nature of ''Active'' Carbon? H. H. Lowry. Practically 

 all investigators have used for their measure of "activity" the adsorp- 

 tive capacity of the carbon (charcoal) under certain arbitrary condi- 

 tions. In several previous papers data have been given which indicate 

 that the adsorptive capacity of carbon is increased by any process 

 which increases either the total surface per unit weight or the degree 

 of unsaturation of the surface atoms, or both. No exceptions to this 

 generalization have been encountered. Since the adsorptive capacity 

 is dependent on two factors which may be independently varied, it 

 seems hardly logical to continue its use as a measure of the activity of 

 carbon. Since it is generally recognized that the forces effective in 

 adsorption processes are a result of the unsaturation of the surface 



* Proc. The Inst. Radio Engiiieers, Feb. 1930. 

 ''Jour, of Fhys. Cliem., Jan. 1930. 



