THE COMPANDOR 331 



Results of Compandor Operation 



The effectiveness of the compandor in service depends not only on 

 its abiUty to reduce noise but also on its relation to the other character- 

 istics of the circuit. Tests in the laboratory and on the long-wave 

 transatlantic circuit have indicated that the presence of the compandor 

 does not affect the quality appreciably, provided compressor circuit 

 No. 2 is employed and provided the compression in the circuit itself 

 is not serious. Delay distortion can be tolerated up to about the same 

 amount as when no compandor is used. Frequency changing for 

 privacy purposes is not materially affected by the compandor. 



The expander increases the transmission variations in the circuit 

 exactly as it increases the voltage range of the waves applied to it. 

 It is therefore necessary to guard against excessive variations in the 

 overall circuit including the wire line extensions as well as the radio 

 links. At the New York terminal there has been installed an automatic 

 volume control operated from received speech signals which performs 

 this function. 



The received volume is limited by incoming waves which do not 

 operate the receiving side of the vodas but which return as echoes from 

 the land line to cause false operation of the transmitting side. The 

 compressor increases these weak waves so that they are better able to 

 operate the receiving side of the vodas, and the expandor effectively 

 increases the stronger waves relative to the weak. This results in more 

 received volume being delivered to the two-wire terminal than when the 

 compandor is not used. The overall improvement in volume delivered 

 to the subscriber varies with the noise, being greatest when the noise is 

 low. 



Summary 



The allowable increase of about 5 db in noise before reaching the 

 commercial limit increases the time when the circuit can be used for 

 service. The increased circuit time is greatest in the seasons of the 

 year when it is needed the most. 



For conditions of moderate disturbances now classed as commercial, 

 a reduction of the noise transmission impairment to very low values is 

 accomplished by the compandor. 



The improvement in the vodas operation results in delivering sub- 

 stantially higher volumes to the subscribers. 



The beneficial effect of the compandor might alternately be ap- 

 plied to a reduction of transmitter power. 



