. The Bell System technical journal . g steps at the sending end andthe two demodulating steps at the receiving end in four lines beginningat the top. A carrier of 2376 kc. is used for the first modulation,which results in a lower sideband from 1570 to 2376 kc. and an upper 450 BELL SYSTEM TECHNICAL JOURNAL sideband from 2376 to 3182. The carrier itself is eliminated in thebalanced modulator. The output of this modulation is passed througha filter, but because the two sidebands touch each other at 2376 kc,the filter cannot cut ofif all the upper sideband. At the output ofthis filter there is t
. The Bell System technical journal . g steps at the sending end andthe two demodulating steps at the receiving end in four lines beginningat the top. A carrier of 2376 kc. is used for the first modulation,which results in a lower sideband from 1570 to 2376 kc. and an upper 450 BELL SYSTEM TECHNICAL JOURNAL sideband from 2376 to 3182. The carrier itself is eliminated in thebalanced modulator. The output of this modulation is passed througha filter, but because the two sidebands touch each other at 2376 kc,the filter cannot cut ofif all the upper sideband. At the output ofthis filter there is thus the lower sideband plus a small amount of thelower part of the upper sideband. The upper sidebands from allsubsequent modulations are readily eliminated by filters because ofthe wide separation. TRANSMITTING END RETAINED UPPER _j V^ SIDE-BAND ^ PASSED LOWER_J,^_ .pcTFD-J mu. 2376 (CARRIER)(FIRST MODULATION) LOWER SIDE-BANDTRANSMITTED OVER LINE REJECTED -- UPPER >| SIDE-BAND ! 2520 (CARRIER)(SECOND MODULATION) RECEIVING END. 0 °° 2376 (CARRIER) ^^^^ (SECOND demodulation) FREQUENCY IN KILOCYCLES PER SECOND Fig. 11—Schematic diagram illustrating the processes of modulation and demodulationused in transmitting television signals over the coaxial line. The carrier for the second modulation is 2520 kc, and the lowersideband extends from 950 down to 144 kc. plus a vestigial uppersideband remaining from the first modulation which extends down to120 kc. The high-pass filter following this modulation is accuratelydesigned to pass with controlled attenuation a group of frequenciesjust above 144 kc. and the vestigial sideband. The resulting singlesideband, extending from 120 to 950 kc, is then passed over thecoaxial cable. At Philadelphia the received signal, together with a carrier of2520 kc, is applied to the first demodulator, and the lower sideband. COAXIAL CABLE SYSTEM FOR TELEVISION TRANSMISSION 451 from 2400 down to 1570, is passed to the second demodulator where acar
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