. The Bell System technical journal . carrier, and the lower trace the lowerside-band. Strips 4, 5 and 6 are from a section of a similar type ofrecord made May 23, 1925, 1:06 , where the carrier was modu-lated with a 500-cycle tone and different filters were used. In thisrecord the upper trace is the lower side-band and the lower trace theupper side-band. It will be noticed that the timing interruption appears only in theside-band signals, as the tone was interrupted before modulationtook place, and that the amplitude of the carrier signal is not affected STUDIES IN RADIO BROADCAST TRANSMI
. The Bell System technical journal . carrier, and the lower trace the lowerside-band. Strips 4, 5 and 6 are from a section of a similar type ofrecord made May 23, 1925, 1:06 , where the carrier was modu-lated with a 500-cycle tone and different filters were used. In thisrecord the upper trace is the lower side-band and the lower trace theupper side-band. It will be noticed that the timing interruption appears only in theside-band signals, as the tone was interrupted before modulationtook place, and that the amplitude of the carrier signal is not affected STUDIES IN RADIO BROADCAST TRANSMISSION 159 by the interruption of the modulating tone. This makes it veryeasy 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 aretransmitted to reproduce one. In Fig. 12, strips 1, 2, and 3, the relative amplitudes of the threesignals are very nearly in proportion to the relative amplitudes of Time. Fig. 12—Fading record showing individually the fading of carrier and side-bandfrequencies. 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. Beforethis record was made a transmission characteristic of the completereceiving circuit, including the oscillograph elements, was obtained,using a local transmitter with modulated carrier for the purpose ofmaking the measurement. The gain of the audio amplifiers at theoutputs of the filters was adjusted to give substantially uniformtransmission on each of the three frequencies corresponding to thecarrier and side bands of the radio frequency signal. As shown in Fig. 11, a telegraph key is placed in the circuit of thecenter oscillogtaph element, for the purpose of placing identifyingsignals on the records. An example of these identifying signals is 160 BELL SYSTEM TECHNICAL JOURNAL shown in Fig. 12, strip 4,
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
