DEVELOPMENT OF A HANDSET FOR TELEPHONE STATIONS 259 



ject each granule to substantially the same heat treatment and produce 

 carbon of unusually uniform electrical properties. Uniformity is fur- 

 ther insured by the use of a magnetic separator to remove granules 

 having an undesirably high iron content, and the removal in an air 

 stream of flat, wedge-shaped particles which tend to cause carbon 

 leakage in the transmitter by working their way between the layers of 

 paper which form the closure between the carbon chamber and dia- 

 phragm. 



Measures of this kind have been of particular value, not only in bet- 

 tering the transmission characteristics of the individual transmitter, 

 but in securing a uniform commercial product. Without these im- 

 provements, indeed, it is doubtful if the production of the transmitter 

 could be maintained at the high rate now required without a sacrifice 

 in the average quality of the product. 



Receiver 



The parts of the handset receiver are assembled in a die cast alum- 

 inum housing, and form a unit which mounts in a threaded bushing in 

 the handle in much the same manner as the transmitter unit. One 

 connection to the winding is made through the threaded portion of the 

 case, the other through a contact spring in the base. The cap and 

 spacing ring are made of phenol plastic and thoroughly insulate the 

 metal parts so that the user cannot come in contact with any portion 

 of the receiver which forms a part of the electrical circuit. The spac- 

 ing ring also serves as a lock ring for holding the receiver on the handle. 

 A grid in the cap prevents damage to the diaphragm from the project- 

 ing portions of the mounting. The layout of the holes in the grid is 

 such that a dent in the diaphragm caused by inserting a pencil or 

 other sharp object through the grid, will not occur at a point over the 

 pole faces and interfere with the operation of the receiver. 



While in general the design of this receiver follows conventional lines, 

 the choice of materials and the design of the magnetic circuit have re- 

 sulted in an increase in efhciency of several db as compared with the 

 deskstand receiver. It has not been considered desirable, however, 

 to make use directly of this increase in efficiency for several reasons. 



Although greater receiving efficiency raises the intensity of the in- 

 coming speech, it also increases the intensity of any noise present on 

 the line or picked up as sidetone. Since, therefore, the ratio between 

 the received speech and the noise is not improved, the general reception 

 would be little benefited by an increase in receiving efficiency alone. 

 Furthermore, the increased sidetone causes an effective loss in trans- 

 mitting level by causing the speaker to lower the intensity of his speech. 



