COPPER OXIDE MODULATORS IN CARRIER SYSTEMS 319 



present in the five circuits already shown. Third order modulators in 

 which the copper oxide is arranged to give equal interruptions to the 

 signal in both positive and negative half cycles of the carrier are excep- 

 tions not considered here. In addition, circuits like Hartley's, in 

 which phase discriminations have been obtained in the sideband out- 

 puts from two modulators by altering both the carrier and signal input 

 phase of one, can be viewed as composed of two modulators of any of 

 the types illustrated. 



In these copper oxide modulators all modulation product frequencies 

 can be grouped into four classes: 



UqC ± TIqV, 

 floC ± UeV, 

 fleC ± nov, 



UeC ± rieV, 



in which c and v are the carrier and input signal frequencies and wo is 

 any odd number 1, 3, 5 etc., while fie is any even number 0, 2, 4, 6, etc. 

 If c and V contain more than one frequency each, Wo and Ue are respec- 

 tively the odd and even combinations of all multiples of the c and v 

 frequencies. All frequencies of one of these four types appear together 

 in a specific branch of the modulator circuit; and they will not appear 

 in another branch unless from a dissymmetry among the copper oxide 

 units or unless inherent in the circuit configuration. The branches in 

 which the modulation products appear are shown in the circuits 

 illustrated. It is apparent that only in the case of the double-balanced 

 circuit of Fig. 2c, are all of these types of products completely separated 

 in different parts of the circuit. In the other circuits shown the 

 classes of products appear together in combinations of two types. 

 In any balanced circuit that can be drawn the above relationships 

 will be found to hold. 



Modulation products will be of a type to which the circuit offers 

 some degree of balance, of a type that can be made to vary in im- 

 portance relative to the signal by adjustment of either the carrier or 

 signal voltage, or of a type to which neither balance nor level adjust- 

 ment is of any benefit. Satisfactory operation of such modulators 

 requires large carrier voltages relative to those of the signal, so that 

 products like c ± z^, 2c ± z;, 3c db v, etc. tend to be of large magnitude 

 while products like c ± 2z;, c ± ?>v, etc. tend to be small. Further- 

 more, the former types can be made to predominate even more over 

 the latter types either by increasing the carrier amplitude or by de- 

 creasing the signal levels. A 6 db reduction in signal results in 12 db 

 reduction oi c ±. 2v and 18 db reduction in c ± 2>v. In any circuit 



