Figure 1-6. Vertical and horizontal polarization.
(2) As described above, when the RF carrier is modulated by complex tones such as speech,
each separate frequency component of the modulating signal produces its own upper and lower sideband
frequencies as shown in Figure 1-8, page 1-11. These additional frequencies occupy a band of
frequencies which are called sidebands. The sideband that contains the sum of the RF and AF signals is
called the upper sideband. The sideband that contains the difference between the RF and AF signals is
called the lower sideband.
(3) The space occupied by a carrier and its associated sidebands in the radio frequency
spectrum is called a channel. In AM, the width of the channel (bandwidth) is equal to twice the highest
modulating frequency. For example, if a 5000 kHz (5 MHz) carrier is modulated by a band o
frequencies ranging from 200 to 5000 cycles (.2 to 5 kHz), the upper sideband extends from 5000.2 to
5005 kHz. The lower sideband extends from 4999.8 kHz to 4995 kHz. Thus, the bandwidth is the
difference between 4995 kHz and 5005 kHz, a total of 10 kHz.
1-9
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