DEVELOPMENT OF A HANDSET FOR TELEPHONE STATIONS 253 



deskstand service it renders this type of transmitter unsuitable for the 

 more severe conditions encountered in the use of a handset. 



Effect of Angular Position on Carbon Noise 



Another transmitter characteristic which is likely to be influenced 

 by the position in which the handset is held is carbon noise. In addi- 

 tion to the adsorbed gas on the surface of the granule there is also an 

 appreciable amount of gas absorbed in the pores in its surface.^ When 

 a voltage is impressed on the transmitter the temperature ^ of the 



35 



30 



25 



20 



Z 15 



5 







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



ANGULAR POSITION IN DEGREES 



FACE UP FACE DOWN 



/ 



y' 



\ 



Ol ^ I ) ll80 



^J 



180 



a. 



Fig. 7 — Effect of position on carbon noise. 



points of contact between the granules is increased and a certain 

 amount of the gas is driven off, forcing the granules apart and giving 

 rise to non-periodic changes in resistance. These disturbances result 

 in noise in the receiver which tend to mask incoming speech. It is 

 evident that a given efflux of gas will produce a larger change in resist- 

 ance when the contact forces are low than when they are high. Hence, 

 if as a result of turning the transmitter through the various angles in 

 which it is likely to be used, the contact pressure is lowered and the 

 resistance raised, a sufficient increase in temperature may occur to 

 cause a vigorous evolution of gas and increased noise. It would, 

 therefore, seem reasonable to expect that, inasmuch as the contact 



*"The Effect of Gases on the Resistance of Granular Carbon Contacts," P. S. 

 Ohnstead, Journal of Physical Chemistry, Jan. 1929, pp. 69-80. 



^ " Cber Kontaktwiderstande besonders bei Kohlekontakten," Von Ragnar Holm, 

 Zeitschrijt fiir Technische Physik, Sept. 1922, pp. 290-294, Oct. 1922, pp. 320-326, 

 and Nov. 1922, pp. 349-357. 



