254 



BELL SYSTEM TECHNICAL JOURNAL 



pressures and the resistance of the handset transmitter are substan- 

 tially independent of angular position, the change in noise with posi- 

 tion would be practically negligible. That this condition is realized is 

 evident from the data shown in Fig. 7. Not only is the average carbon 

 noise negligible even under severe conditions of service, but the maxi- 

 mum variation of the noise in any position of the transmitter is only 

 about one db. On the other hand, the noise developed by a typical 

 deskstand transmitter in the optimum position is approximately five 



^ 



Q 



Z -10 



I- 



D -20 



180 150 120 90 60 30 30 60 90 120 160 180 



ANGULAR POSITION IN DEGREES 



FACE UP FACE DOWN 



— |— ^ 0| 7 — I — ^ 1 ISO 



/ I '^^ I \ 



o \ y \ J 1180 



"^y 



Fig. 8 — Effect of position on transmitter output. 



db higher, and in its worst position nearly thirty db higher than the 

 noise produced by the handset transmitter. Noise of such a magni- 

 tude would constitute an appreciable transmission impairment. 



Effect of Angular Position on Output 

 One of the unique features of this new handset transmitter is the 

 fact that the carbon chamber is located in front rather than in back of 

 the diaphragm as has been customary in the past. By adopting this 

 arrangement the carbon granules are held in intimate contact with the 

 diaphragm in all of the positions in which the handset is likely to be 

 held and uniform output and faithful reproduction of the speech sounds 

 obtained. There are, however, angular positions in the region of 90 

 degrees face down where the carbon tends to fall away from the dia- 

 phragm, but as is shown by curve A, Fig. 8, the resultant loss in the 



