DKVKLOPM/'.NT OF A Il.l XDSET FOR TELFFHONK STA'FIOXS 251 



transmitter, insulate the metal parts in the electrical circuit so that 

 they cannot come into contact with the user. The spacing ring also 

 serves to lock the transmitter to the handle and align the mouthpiece 

 with the axis of the handle. 



Effect of Angular Position on Resistance 



The carbon chamber of the transmitter is often referred to as a 

 "barrier" type and differs radically from the conventional form of 

 " direct action " resistance element, which has been employed for years 



180 150 



!0 90 60 30 30 60 90 120 150 180 



ANGULAR POSITION IN DEGREES 

 FACE UP FACE DOWN 



OL 



r=f^ 





TIBO 



Fig- 5 — Effect of position on transmitter resistance. 



in deskstand transmitters. In the direct action type the movable 

 member not only transmits the acoustic forces on the diaphragm to the 

 carbon but also serves as an electrode. Both electrodes of the barrier 

 type are stationary and a thin layer of phenol varnish insulates the 

 diaphragm from the carbon. A ceramic barrier "* separates the elec- 

 trodes from one another and defines the current path through the 

 carbon. The electrode surface adjacent to the diaphragm is cylindri- 

 cal in shape, the other hemispherical. Both are gold plated. By 

 adopting this electrode arrangement good contact is maintained be- 



* "Manufacture of Thin Porcelain Parts of Close Dimensional Tolerances," L. I. 

 Shaw, A. O. Johnson and W. J. Scott, Journal of Ceramic Society, Nov. 1931, pp. 

 851—854. 



