STUDIES IN RADIO BROADCAST TRANSMISSION 



159 



by the interruption of the modulating tone. This makes it very 

 easy to identify the side-band signals. These records give an ex- 

 cellent graphic picture of ordinary radio telephone transmission, 

 bringing out the fact that three truly individual frequencies are 

 transmitted to reproduce one. 



In Fig. 12, strips 1, 2, and 3, the relative amplitudes of the three 

 signals are very nearly in proportion to the relative amplitudes of 



Time 



Fig. 12 — Fading record showing individually the fading of carrier and side-band 

 frequencies. Made at Riverhead, L. I. Timing interruptions in side-band signals, 5 



seconds apart 



the signals as they existed in the ether at the receiving point. Before 

 this record was made a transmission characteristic of the complete 

 receiving circuit, including the oscillograph elements, was obtained, 

 using a local transmitter with modulated carrier for the purpose of 

 making the measurement. The gain of the audio amplifiers at the 

 outputs of the filters was adjusted to give substantially uniform 

 transmission on each of the three frequencies corresponding to the 

 carrier and side bands of the radio frequency signal. 



As shown in Fig. 11, a telegraph key is placed in the circuit of the 

 center oscillogtaph element, for the purpose of placing identifying 

 signals on the records. An example of these identifying signals is 



