320 



BELL SYSTEM TECHNICAL JOURNAL 



application interferences of this type lend themselves to reduction 

 in so far as carrier power is available for high signal level operation, or 

 in so far as noise does not limit for low signal levels. Laboratory 

 measurements of some of these modulation products made during the 

 development of a group modulator for a twelve-channel open-wire 

 carrier system are shown in Fig. 3 for a double-balanced modulator 



-40 -35 -30 -25 -20 -15 -'0 -5 



output of lower sideband (c-v) in decibels 

 (below 0.006 watt) 



-10 -5 5 10 



CARRIER LEVEL IN DECIBELS' 

 (FROM 0.75 volt) 



Fig. 



3 — Intensity of modulation products in a representative double-balanced 

 copper oxide modulator. 



like that of Fig. 2(c). Single 3/16 inch diameter discs as shown in Fig. 1 

 were used in each bridge arm. About 20 to 30 db reduction in inter- 

 ference by balance alone is quite readily obtained in the normal run 

 of manufactured copper oxide rectifier elements, for those products 

 to which the circuit arrangement offers a balance. Any further 

 improvement must be obtained either by closer control of manufacture 



