|[AMRadio] Physical Reality of Sidebands|
bbruhns at erols.com
Mon Jan 17 14:17:54 EST 2005
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.
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