ABSTRACTS OF TECHNICAL ARTICLES 597 



study and development of apparatus are stated to be drawing to a close, 

 and we are said to be well advanced toward the third and last period — 

 that of general application to commercial flying. 



The discussion of radio-communication outfits is based on aircraft 

 equipment recently developed by the Bell Telephone Laboratories for 

 receiving weather reports and beacon signals and for two-way tele- 

 phonic communication between the airplane and ground stations. 



Units of different types of apparatus for use in small mail-planes and 

 in large transports are illustrated and described, together with tabular 

 data of sizes and weights of individual units of both general types of 

 outfit. 



Information regarding the requirements of shielding, bonding and 

 installation is given, and the airplane factory is stated to be the place 

 where provisions for radio installation can best be made. If suitable 

 provisions have been made therefor, the installation of two-way radio 

 equipment is said to be simple and inexpensive. 



A number of the larger air-transport organizations have made note- 

 worthy progress toward providing suitable radio systems and the De- 

 partment of Commerce is giving much assistance in the way of radio 

 aids to air navigation, but a great deal of work remains to be done by the 

 industry as a whole and numerous problems will require solution. 

 New requirements will be encountered as the number and size of air- 

 planes increase, but continuing radio studies promise that the develop- 

 ment of aircraft radio communication will keep abreast of the develop- 

 ment of airplanes. 



Transmission Characteristics of a Short- Wave Telephone Circuit.^ 

 R. K. Potter. A method of observing and recording the audio- 

 frequency transmission characteristics of a short-wave radiotelephone 

 channel is described. These characteristics undergo rapid changes. 

 They appear to be the result of wave interference between signals arriv- 

 ing at the receiver over paths of different group or electrical length 

 possibly combined with the distortion produced by a progressive change 

 in the angle of rotation of the polarization plane with frequency over 

 the signal band. The persistence of certain pattern shapes during the 

 observation periods and the changes in these shapes from hour-to-hour 

 suggest that they are the result of progressive rather than erratic dis- 

 turbances in the transmission medium. Times when the audio-fre- 

 quency characteristics were flat were very rare. However, a consider- 



^ Proc. Inst. Radio Engineers, Apr., 1930. 



