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BELL SYSTEM TECHNICAL JOURNAL 



equipped with radio field-measuring apparatus of the Laboratories' 

 design. With this plane exact measurements can be made at various 

 altitudes under different weather conditions of the efficiency of radio 

 transmission from the Whippany transmitter. In addition the plane 

 carries radio transmitting and receiving sets of experimental design. 



Fig. 2. The Cabin Monoplane for Experiment in 

 Airways Communication. 



It is, in fact, a flying radio laboratory in which the engineers may 

 experiment under actual flying conditions. 



Whether a radio beacon service and a radio telephone service at 

 ail the various airports over the country can be made practicable is 

 largely a question of available ether channels. By international 

 agreement, the frequency band 285-315 kcs. (1050-950 meters) is 

 reserved for radio beacons, both marine and air service. F'or "air 

 mobile service exclusively" there is reserved the band 315-350 kcs. 

 (950-850 meters) in which the 900 meter wave {333 kcs.) is reserved 

 as an air service calling wave and is not to be assigned. 



Radio telephony requires a band of frequencies sufficiently wide to 

 include the "side bands" of speech frequency. For distinct trans- 

 mission of speech, neglecting certain requirements of musical quality, 

 this might require a minimum of 6,000 cycles. In this band reserved 

 for "air mobile service exclusively" there is room, therefore, for but 



