Single Side Band (SSB)  Frequency Modulation (FM) 11-36 Figure 11-82.  The bandwidth of an AM signal contains the carrier  wave, the carrier wave plus the information signal frequencies, and  the carrier wave minus the information signal frequencies.  Figure 11-81.  A frequency modulated (FM) carrier wave retains  the consistent amplitude of the AC sign wave. It encodes the unique  information signal with slight variations to the frequency of the  carrier wave. These variations are shown as space variations  between the peaks and valleys of the wave on an oscilloscope.  Frequency modulation (FM) is widely considered superior  to AM for carrying and deciphering information on radio  waves. A carrier wave modulated by FM retains its constant  amplitude. However, the information signal alters the  frequency of the carrier wave in proportion to the strength of  the signal. Thus, the signal is represented as slight variations  to the normally consistent timing of the oscillations of the  carrier wave.  [Figure 11-81] Since the transmitter oscillator output fluctuates during  modulation to represent the information signal, FM bandwidth  is greater than AM bandwidth. This is overshadowed by the  ease with which noise and static can be removed from the  FM signal. FM has a steady current flow and requires less  power to produce since modulating an oscillator producing a  carrier wave takes less power than modulating the amplitude  of a signal using an amplifier. Demodulation of an FM signal is similar to that of an AM  receiver. The signal captured by the receiving antenna is  usually amplified immediately since signal strength is lost as  There are a limited number of frequencies within the usable  frequency ranges (i.e., LF, HF, and VHF). If different  broadcasts are made on frequencies that are too close  together, some of the broadcast from one frequency interfere  with the adjacent broadcast due to overlapping side bands.  The FCC divides the various frequency bands and issues  rules for their use. Much of this allocation is to prevent  interference. The spacing between broadcast frequencies  is established so that a carrier wave can expand to include  the upper and lower side bands and still not interfere with a  signal on an adjacent frequency.  Due to the fluctuating nature of the information signal, the  modulating frequency varies from the carrier wave up or  down to the maximum amplitude of the modulating frequency  during AM. These additional frequencies on either side of the  carrier wave frequency are known as side bands. Each side  band contains the unique information signal desired to be  conveyed. The entire range of the lower and upper sidebands  including the center carrier wave frequency is known as  bandwidth.  [Figure 11-82]  When two AC signals are mixed together, such as when a  carrier wave is modulated by an information signal, three  main frequencies result: the wave travels through the atmosphere. Numerous circuits  are used to isolate, stabilize, and remove the information  from the carrier wave. The result is then amplified to drive  the output device. 1.  Original carrier wave frequency;  2. Carrier wave frequency plus the modulating  frequency; and 3.  Carrier wave frequency minus the modulating  frequency.  Lower side bands Upper side bands AM bandwidth Carrier Modulating signal FM signal