CARRIER AND SIDE-BANDS IN RADIO TRANSMISSION 99 



direction of the signaling current the effect of the second tube pre- 

 dominates and radio frequency is again transmitted, this time with the 

 phase reversed, owing to the differential connection. The wave form 

 of a signaling current and the resulting output current are roughly 

 as shown in Fig. 4, A and B. If this output be amplified for trans- 



SPEECH WAVE 



SUM OF THE TWO SIDE-BANDS 

 RESULTING FROM THE SPEECH WAVE. 



Fig. 4. 



mission there will be no load on the amplifier and antenna except 

 during actual speech, when it will be proportional to the intensity of 

 the speech. 



That these intermittent pulses of carrier frequency produced by a 

 balanced modulator are equivalent to a modulated wave from which 

 the carrier frequency component has been removed, may be easily 

 shown. Consider a single sinusoidal component 5 cos (qt-\-Q), of 

 the signaling wave which is applied to the balanced modulator. The 

 resulting output current is a wave of carrier frequency, the amplitude 

 of which is proportional to C and to S and varies cyclically with a fre- 

 quency £- between the values -\-K C S and —KCS, where K is a 



