[AMRadio] Physical Reality of Sidebands |
Bob Bruhns
bbruhns at erols.com
Mon Jan 17 14:17:54 EST 2005
Hi Gary, The carrier is not multiplied with the sideband frequencies to generate AM, it is multiplied with the baseband modulating frequency. In my example, three sine waves corresponding to a carrier and two sideband frequencies are added together to produce the AM signal, but a relatively low frequency is multiplied with the carrier in the AM transmitter to produce the carrier and sideband frequencies in the reverse example. Interestingly, if the AM signal, with or without carrier, is multiplied at the receiver with a regenerated carrier of proper frequency and phase, then the baseband modulating signal is recovered. In the transmitter, the multiplication occurs in the modulated stage. In plate-modulated AM, the carrier is multiplied by the plate voltage. Normalizing plate voltage to unity, it is multiplied by +1 without modulation. Modulation varies the B+, and therefore the multiplication factor. The normalized multiplication factor varies from 0 to +2 with 100% sine wave modulation. Bacon, WA3WDR
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