160 BELL SYSTEM TECHNICAL JOURNAL 



radio station. In such cases the transmitter and its associated ampli- 

 fier are operated and controlled in the same way as described above 

 for toll lines. In some cases the radio station is in the same city as 

 the place where the speech or music is given and in other cases the 

 two have been in different cities. In the first case the output of the 

 transmitter amplifier is carried to the radio station over non-loaded 

 cable circuits which are equalized by means of distortion correction 

 networks to have uniform efficiency over a wide frequency range, in 

 some cases up to 5000 cycles. Where the two points are in different 

 cities, the non-loaded cable circuit goes to the toll office and there is 

 connected to the toll lines which are operated in the same manner as 

 described above for loud speaker use. 



For some of the higher grade music, such as that given by symphony 

 orchestras, the less efficient, but slightly higher quality condenser 

 type transmitter has been used instead of the double button carbon 

 type. This requires the use of an additional two stage amplifier in 

 front of the regular three stage transmitter amplifier. 



The output of the transmitter amplifiers is controlled with the aid 

 of a volume indicator bridged across the output terminals of the ampli- 

 fier. For best results, particularly in reproducing music, it is neces- 

 sary to adjust the gain of these amplifiers to compensate partially for 

 the large range in the volume of the music. If the amplifiers are set 

 high enough in gain to send through the low passages of the music 

 with sufficient volume so that it will override the static and the inter- 

 ference from other sending stations, the loud parts of the music will 

 seriously overload the radio transmitter system, unless it is of very 

 large capacity, and will in general overload the receiving sets. Further- 

 more putting out these loud parts at the same relative level with 

 respect to the low passages as they are given by the orchestra, makes 

 the interference between radio stations more serious. In some or- 

 chestral concerts the power amplification of the transmitter amplifier 

 has been adjusted over a range of more than a hundred to one, these 

 changes being made, however, so that they were not noticed by those 

 listening to the concert by radio. 



Proper volume control is very important in picking up such music 

 for radio broadcasting. The lack of such control is responsible for 

 many of the poor results that are being obtained. In this connection, 

 the location of the transmitter with respect to the various instruments 

 in the orchestra or smaller combination of instruments, so as to main- 

 tain in the reproduced music the proper balance between the several 

 parts is, of course, of great importance. 



An interesting illustration of the combination of the public address 



