TELEPHONE TRANSMITTERS AND RECEIVERS 625 



transmitter. Likewise, the receiving system of the circuit may be 

 considered to consist of the cord circuit, the loop, the set and the re- 

 ceiver. For the connection of such transmitting and receiving systems 

 through a distortionless trunk, the response characteristic of the overall 

 circuit, giving the relation between the power delivered by the receiver 

 and the power available at the transmitter, shows a variation of about 

 30 db in the range from 500 to 2,000 cycles with the maximum response 

 slightly above 1,000 cycles. This characteristic applies to the type of 

 deskstand apparatus which is now the most generally used station 

 equipment in the Bell System. 



With the development of the telephone art numerous ideas have 

 naturally been investigated for improving the performance of the 

 transmitter and the receiver. Taking into account the various con- 

 siderations and possibilities, the present procedure is on the basis that 

 further improvements should come from reduction in distortion rather 

 than from increases in the maximum response. For practical instru- 

 ments the desire is primarily to reduce the distortion without sacri- 

 ficing the average efficiency over the important part of the voice range. 

 Means have been developed for reducing the distortion in these instru- 

 ments but in general such improvements have involved material re- 

 ductions in efficiency. For example, a very high degree of freedom from 

 distortion is realized in the type of carbon transmitter which has been 

 so widely used for pickup work in radio broadcasting. This trans- 

 mitter, however, requires a powerful amplifier to bring its output to 

 a value comparable with the type of transmitter used in commercial 

 telephony. It has been possible also to obtain large reductions in the 

 distortion of the receiver but here, too, large sacrifices in efficiency 

 have attended this accomplishment. Material progress has been made, 

 however, toward the ideal of a combination of low distortion without 

 sacrifice in efficiency. 



Some of these improvements have been incorporated in the trans- 

 mitter which is used in the handset type of station apparatus. The 

 frequency response characteristic of transmitting and receiving systems 

 such as described above, but using the handset instruments instead 

 of the deskstand, shows a variation of only about 20 db in the range 

 from 500 to 2,000 cycles, and with the handset instruments this same 

 variation of 20 db covers the range from 500 to 3,000 cycles. The 

 handset transmitter presents, therefore, a material advance from the 

 standpoint of reducing distortion. 



The proposal has been made at various times that the interference 

 situation might be helped by providing still more efficient transmitters. 

 The various possible means of still further increasing the transmitter 



